{"gene":"NPY","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":1984,"finding":"The human NPY gene encodes a 97-amino acid precursor (preproNPY) that undergoes proteolytic processing at two sites to generate three peptides: a 28-aa signal peptide, the 36-aa mature NPY, and a 30-aa C-terminal peptide. The coding sequence was determined from a human pheochromocytoma cDNA.","method":"cDNA cloning, nucleotide sequencing, in vitro translation with immunoprecipitation, Edman degradation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct sequencing plus biochemical validation of precursor structure","pmids":["6589611"],"is_preprint":false},{"year":1986,"finding":"The human NPY gene spans ~8 kb and contains four exons: exon 1 is non-translated; exon 2 encodes the signal peptide through residue 63 of preproNPY; exon 3 encodes 27 amino acids; exon 4 encodes the C-terminal heptapeptide and 3′ UTR. A TATA-like and CAAT-like sequence are present 25 and 70 bp upstream of the transcription start site, respectively. Approximately 530 bp of 5′ flanking sequence is sufficient for promoter activity in neuronal cell lines (CA-77, PC12).","method":"Genomic library cloning, primer extension, reporter gene (chloramphenicol acetyltransferase) transfection assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — gene structure determined by sequencing plus functional promoter assay","pmids":["2427515"],"is_preprint":false},{"year":1987,"finding":"Synthetic porcine NPY adopts a concentration-independent alpha-helical conformation in aqueous solution at neutral/basic pH (as shown by circular dichroism), with loss of helical content at acidic pH. The peptide is neither wholly monomeric nor dimeric by sedimentation equilibrium, suggesting an intramolecularly stabilized helical structure analogous to avian pancreatic polypeptide. Receptor binding affinity IC50 ~5 nM.","method":"Solid-phase peptide synthesis, circular dichroism spectroscopy, sedimentation equilibrium, radioligand receptor binding assay","journal":"Neuropeptides","confidence":"Medium","confidence_rationale":"Tier 1 — biophysical characterization of synthetic peptide, single study","pmids":["2823169"],"is_preprint":false},{"year":1985,"finding":"NPY is co-localized with noradrenaline in large dense-cored vesicles of sympathetic perivascular neurons. 6-OHDA treatment depletes NPY-immunoreactivity in terminal regions while increasing it in stellate ganglion cell bodies. Reserpine causes dose- and time-dependent depletion of NPY from sympathetic nerve terminals (heart, spleen) dependent on intact nerve activity, but unlike NA, NPY depletion by reserpine is entirely dependent on ongoing neuronal activity. Axonal ligation reveals anterograde axonal transport of NPY at ~3 mm/h, and reserpine significantly increases this transport rate.","method":"Immunohistochemistry, radioimmunoassay, 6-OHDA and reserpine pharmacological lesions, nerve ligation axonal transport assay, HPLC","journal":"Naunyn-Schmiedeberg's archives of pharmacology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (IHC, RIA, pharmacological manipulation, ligation assay) replicated across tissues","pmids":["2858824"],"is_preprint":false},{"year":1985,"finding":"NPY is present in sympathetic perivascular nerves of dental pulp and oral mucosa (co-localized with noradrenaline) and produces potent, long-lasting vasoconstriction resistant to alpha-adrenoceptor blockade by phentolamine and unaffected by guanethidine, demonstrating that NPY acts through a receptor mechanism distinct from adrenoceptors to reduce local blood flow.","method":"Immunohistochemistry, retrograde axonal tracing, HPLC, local 125I-clearance blood flow measurement, pharmacological antagonism (phentolamine, guanethidine)","journal":"Acta physiologica Scandinavica","confidence":"High","confidence_rationale":"Tier 2 — functional vascular assay with pharmacological dissection, multiple tissues","pmids":["2866663"],"is_preprint":false},{"year":1990,"finding":"NPY co-exists with noradrenaline in large dense-cored vesicles and is preferentially released compared to NA upon high-frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited by prejunctional alpha-2 adrenoceptors and adenosine receptors, and facilitated by angiotensin II or beta-receptor activation. NPY itself exerts prejunctional inhibition of both NA and NPY release. A large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cAMP formation, and vasoconstrictor effects. Reserpine-induced NPY synthesis in ganglia is regulated by nicotinic receptor activity.","method":"In vitro organ bath pharmacology, sympathetic nerve stimulation, radioimmunoassay of overflow, receptor binding, cAMP assay, pharmacological dissection","journal":"Fundamental & clinical pharmacology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple functional assays establishing co-transmission mechanism and structure-activity relationships, replicated across vascular beds","pmids":["2170253"],"is_preprint":false},{"year":1992,"finding":"The cloned human NPY Y1 receptor is a G protein-coupled receptor that, when expressed in HEK-293 cells, couples to a pertussis toxin-sensitive Gi protein to inhibit cAMP accumulation. In CHO cells, the same receptor couples instead to elevation of intracellular calcium, demonstrating cell-type-specific second messenger coupling dependent on the available G protein repertoire.","method":"cDNA cloning, heterologous expression in CHO and HEK-293 cells, radioligand binding, cAMP assay, intracellular calcium measurement, pertussis toxin treatment","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in two cell systems with pharmacological and biochemical validation","pmids":["1321422"],"is_preprint":false},{"year":1995,"finding":"The cloned human NPY Y2 receptor (381 aa, 31% identical to Y1) expressed in HEK-293 and CHO cells binds NPY and PYY with high affinity but binds [Leu31,Pro34]NPY with low affinity, and binds truncated NPY13-36 with high affinity — confirming Y2 pharmacological profile. The Y2 receptor inhibits forskolin-stimulated cAMP and increases intracellular Ca2+ when stably expressed in CHO cells.","method":"Expression cloning from hippocampal cDNA library, radioligand binding (125I-PYY), cAMP assay, intracellular calcium measurement in stably transfected CHO cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — expression cloning plus functional characterization in two independent reports (PMIDs 7592910 and 7559383)","pmids":["7592910","7559383"],"is_preprint":false},{"year":1995,"finding":"A novel human NPY receptor (PP1/Y4) with 43% amino acid identity to Y1 was cloned; it binds pancreatic polypeptide with highest affinity (Ki 13.8 pM), PYY with 1.44 nM, and NPY with 9.9 nM — pharmacologically distinguishing it from Y1 and Y2. In stably transfected CHO cells, this receptor inhibits forskolin-stimulated cAMP synthesis via Gi.","method":"Homology-based cloning from human cDNA, radioligand binding, cAMP assay in stably transfected CHO cells, Northern blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — cloning plus pharmacological and functional characterization","pmids":["7493937"],"is_preprint":false},{"year":1996,"finding":"Leptin receptor mRNA co-distributes with NPY-expressing neurons in the ventromedial subdivision of the hypothalamic arcuate nucleus, demonstrated by in situ hybridization of semi-adjacent sections, establishing that leptin receptors are expressed on NPY neurons.","method":"In situ hybridization on mouse brain sections with probes for leptin receptor mRNA and NPY mRNA on semi-adjacent sections","journal":"Neuroreport","confidence":"Medium","confidence_rationale":"Tier 3 — co-distribution by ISH, single study, anatomical co-localization without direct functional coupling","pmids":["9116246"],"is_preprint":false},{"year":1996,"finding":"Antisense oligodeoxynucleotides targeting the NPY Y1 receptor mRNA, microinjected into the rat ventromedial hypothalamus, suppress NPY-induced feeding and cause hypothermia and body weight reduction, establishing that Y1 receptors in the VMH are necessary for NPY-induced feeding and thermoregulatory responses.","method":"Antisense oligodeoxynucleotide knockdown of Y1R in VMH, food intake measurement, body temperature telemetry, locomotor activity monitoring","journal":"Proceedings. Biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with specific phenotypic readout, single study","pmids":["8760491"],"is_preprint":false},{"year":1997,"finding":"NPY acting on Y2 receptors in the dorsal vagal complex (DVC) mimics PYY's suppression of TRH-stimulated gastric motility, while Y1 receptor activation in the DVC stimulates gastric motility from basal conditions. The direction of NPY's effect on gastric motility depends on which receptor subtype is activated and the basal state of stimulation.","method":"Microinjection of selective Y1 and Y2 agonists/antagonists into rat DVC, in vivo gastric motility recording, pharmacological dissection","journal":"Neurogastroenterology and motility","confidence":"Medium","confidence_rationale":"Tier 2 — selective agonist/antagonist pharmacology with direct physiological readout","pmids":["9198086"],"is_preprint":false},{"year":1998,"finding":"NPY-deficient mice (preproNPY knockout) show increased ethanol consumption and reduced sensitivity to the sedative/hypnotic effects of ethanol (faster recovery from ethanol-induced sleep at equivalent plasma ethanol levels). Conversely, transgenic mice overexpressing NPY in neurons show lower ethanol preference and enhanced sedative sensitivity. These results establish an inverse relationship between brain NPY levels and ethanol consumption/resistance.","method":"Targeted gene disruption (NPY-/- mice), transgenic NPY overexpression, two-bottle choice ethanol consumption assay, ethanol-induced sleep/loss-of-righting-reflex test, plasma ethanol measurement","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — reciprocal genetic manipulation (KO and OE) with clear behavioral phenotype, replicated across genotypes","pmids":["9845072"],"is_preprint":false},{"year":1999,"finding":"The inhibitory effect of centrally administered NPY on LH secretion is predominantly mediated by the Y5 receptor subtype: selective Y5 agonists (PYY3-36, human PP, [D-Trp32]NPY) inhibited LH release, while selective Y2 and Y4 agonists did not. A non-peptidic Y5 receptor antagonist (icv, 6–100 μg) dose-dependently blocked NPY-induced LH suppression and also inhibited NPY-stimulated food intake.","method":"Intracerebroventricular administration of selective NPY receptor agonists/antagonists in castrated rats, plasma LH RIA, competitive radioligand binding with Y5-specific assay","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — systematic pharmacological receptor subtype dissection with multiple agonists/antagonists and biochemical endpoint","pmids":["10465275"],"is_preprint":false},{"year":1999,"finding":"NPY Y5 receptor activation mediates both the feeding response and reductions in energy expenditure: selective Y5 agonist D-[Trp32]-NPY (icv) stimulates food intake, reduces brown adipose tissue temperature, and decreases whole-body oxygen consumption, while Y1-, Y2-, and Y4-selective agonists do not reproduce these metabolic effects.","method":"ICV administration of receptor-selective NPY analogs in rats, food intake measurement, implanted BAT temperature transponders, indirect calorimetry","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological receptor subtype dissection with multiple physiological readouts, single study","pmids":["10564216"],"is_preprint":false},{"year":2000,"finding":"Human adipocytes express Y1 receptor (detected by RT-PCR and high-affinity radioligand binding with Y1-selective probes); Y1 receptor activation by NPY/PYY produces antilipolytic effects and enhances leptin secretion from adipocytes. These effects are blocked by selective Y1 antagonists (SR120819A, BIBP3226) and by pertussis toxin-insensitive GTPγS-binding, confirming Gi-coupled Y1 receptor signaling.","method":"RT-PCR, radioligand binding (125I-PYY, 125I-[Leu31,Pro34]PYY), [35S]GTPγS binding, lipolysis assay in isolated human adipocytes, leptin secretion ELISA, selective antagonist pharmacology","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods in human primary cells with functional readouts","pmids":["10858507"],"is_preprint":false},{"year":2000,"finding":"In goldfish, central (ICV) administration of the Y1-like receptor agonist [Leu31,Pro34]-NPY stimulates food intake to the same extent as NPY, while the Y2 agonist does not; this effect is blocked by the general NPY antagonist NPY(27-36). Furthermore, the opioid antagonist naloxone (ICV) blocks NPY-induced feeding, demonstrating that NPY's orexigenic effect in fish is mediated via Y1-like receptors and requires intact opioidergic signaling.","method":"ICV microinjection of selective NPY receptor agonists and antagonists in goldfish, food intake measurement, opioid antagonist (naloxone) pretreatment","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection with epistasis between NPY and opioid systems, single study in teleost model","pmids":["11068096"],"is_preprint":false},{"year":2000,"finding":"Y1 receptor knockout mice (Y1-/-) show dramatically reduced NPY-induced food intake after ICV NPY administration, establishing Y1 as the dominant receptor mediating NPY-induced feeding. Y5 receptor knockout mice show only partial reduction of feeding induced by Y5-preferring agonists but not NPY itself. Additionally, food intake induced by Y5-preferring agonists (PYY3-36, human/bovine PP) is reduced in Y1-/- mice, indicating indirect modulation through Y1 signaling.","method":"Y1-/- and Y5-/- knockout mouse generation, ICV administration of NPY and receptor-selective analogs, food intake measurement","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal genetic KO models with defined pharmacological challenges","pmids":["10698177"],"is_preprint":false},{"year":2001,"finding":"Ghrelin administered ICV strongly stimulates feeding in rats and activates Fos protein in NPY/AgRP neurons in the arcuate nucleus. Antibodies and antagonists against NPY and AgRP abolish ghrelin-induced feeding. Ghrelin augments NPY gene expression in the hypothalamus and blocks leptin-induced feeding suppression, placing NPY downstream of ghrelin and in competitive interaction with leptin in feeding regulation.","method":"ICV ghrelin injection, Fos immunohistochemistry, anti-NPY/AgRP antibody neutralization, NPY/AgRP antagonist pharmacology, RT-PCR for NPY mRNA, leptin interaction experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (IHC, neutralizing antibodies, antagonists, mRNA), replicated in ghrelin-deficient GH context","pmids":["11196643"],"is_preprint":false},{"year":2001,"finding":"Fasting increases hypothalamic NPY and AGRP mRNA in parallel when leptin levels fall; leptin infusion (48 h via subcutaneous osmotic pump) in fasted lean rats almost completely reverses fasting-induced increases in both NPY and AGRP mRNA and restores POMC mRNA. In contrast, leptin-receptor-deficient Zucker (fa/fa) rats show upregulation of NPY but not AGRP mRNA, demonstrating that leptin acts via its receptor on arcuate neurons to suppress NPY expression.","method":"Solution hybridization/S1 nuclease protection assay for hypothalamic NPY, AGRP, POMC mRNA; subcutaneous leptin infusion; leptin receptor mutant rat models (Koletsky, Zucker fa/fa)","journal":"Journal of neuroendocrinology","confidence":"High","confidence_rationale":"Tier 2 — leptin replacement experiment with specific mRNA readouts, replicated in two receptor-mutant rat models","pmids":["11737554"],"is_preprint":false},{"year":2002,"finding":"Antidepressant-like activity of ICV NPY in the mouse forced swimming test is mediated via the Y1 receptor subtype: the Y1 agonist [Leu31,Pro34]PYY mimics NPY's anti-immobility effect; Y1 antagonists (BIBO3304, BIBP3226) block NPY's effect; Y2 agonist NPY(13-36) has no anti-immobility effect at tested doses; Y2 antagonist BIIE0246 is active but may reflect locomotor changes.","method":"ICV drug administration in mice, forced swimming test (immobility time), open field locomotor activity measurement, receptor-selective agonist/antagonist pharmacology","journal":"Neuropsychopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic receptor subtype pharmacology with behavioral endpoint and locomotor controls","pmids":["11927186"],"is_preprint":false},{"year":2003,"finding":"Ghrelin directly activates NPY neurons in the rat arcuate nucleus via Ca2+ signaling: single isolated ARC neurons respond to ghrelin (10-12–10-8 mol/L) with increased [Ca2+]i; ~80% of ghrelin-responsive neurons are NPY-immunopositive. The Ca2+ response is blocked by PKA inhibitors but not PKC inhibitors, and by N-type but not L-type Ca2+ channel blockers. Leptin attenuates ghrelin-induced Ca2+ increases in NPY neurons; orexin is additive with ghrelin.","method":"Enzymatic dissociation of rat ARC neurons, fura-2 single-cell Ca2+ imaging, immunocytochemical NPY identification, selective kinase inhibitors and channel blockers, glucose-sensing neuron identification","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 1 — direct single-neuron Ca2+ imaging with pharmacological dissection of signaling cascade, NPY identity confirmed by immunocytochemistry","pmids":["12663466"],"is_preprint":false},{"year":2003,"finding":"Chronic ICV infusion of the selective Y5 agonist D-Trp34NPY in C57BL/6J mice produces hyperphagia, obesity, increased adiposity, hyperinsulinemia, hyperleptinemia, and hypercholesterolemia; all effects are fully blocked by oral administration of a selective Y5 antagonist. Under pair-feeding, Y5 activation still reduces hormone-sensitive lipase activity in white adipose tissue and decreases UCP-1 mRNA in brown adipose tissue, indicating that Y5-mediated obesity involves both hyperphagia and metabolic changes (decreased lipolysis and thermogenesis).","method":"ICV infusion via osmotic minipump, pair-feeding paradigm, selective Y5 antagonist oral dosing, adipose tissue enzyme activity assay, UCP-1 RT-PCR","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — selective agonist plus antagonist rescue, pair-feeding controls dissect metabolic from caloric mechanisms","pmids":["12697685"],"is_preprint":false},{"year":2003,"finding":"NPY suppresses experimental autoimmune encephalomyelitis (EAE) via Y1 receptors: exogenous NPY and Y1 receptor agonists significantly inhibit EAE induction, while Y5 agonist or combined NPY + Y1 antagonist treatment does not. Y1 antagonist alone produces earlier EAE onset, demonstrating a protective role of endogenous NPY. The Y1 agonist inhibits myelin oligodendrocyte glycoprotein-specific Th1 responses and biases autoimmune T cells toward Th2, directly affecting T cells through Y1 receptors.","method":"Active EAE induction in C57BL/6 mice, selective NPY receptor agonist/antagonist treatment, clinical disease scoring, ex vivo T cell cytokine profiling, antigen-specific proliferation assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — receptor-specific pharmacology with loss-of-function (antagonist) and gain-of-function (agonist), ex vivo mechanistic validation","pmids":["14500640"],"is_preprint":false},{"year":2008,"finding":"NPY molecular recognition by Y receptors involves distinct binding poses: one conserved aspartate residue in the third extracellular loop is essential for ligand binding across all four Y receptors (Y1, Y2, Y4, Y5) but interacts with different arginine residues in the ligand depending on receptor subtype. The N terminus of NPY forms extensive interactions with Y1 but not with Y2 or Y4 receptors. These subtype-specific contacts were mapped by combining chemically modified peptide analogs, receptor mutagenesis, and chimeric receptors.","method":"Receptor mutagenesis (site-directed), chimeric receptor construction, peptide analog synthesis with chemical modifications, radioligand binding in transfected cells","journal":"Nutrition","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis plus chimeric receptors with multiple ligand variants, multiple receptor subtypes","pmids":["18725086"],"is_preprint":false},{"year":2008,"finding":"Ghrelin activates NPY/AgRP neurons through a UCP2-dependent mitochondrial mechanism. Ghrelin induces hypothalamic mitochondrial proliferation and electrical activation of NPY/AgRP neurons; these effects require UCP2. The UCP2-dependent mechanism is driven by a fatty acid oxidation pathway involving AMPK and CPT1, which generates free radicals that are scavenged by UCP2, thereby altering mitochondrial respiration and NPY/AgRP neuronal excitability. Ghrelin-triggered synaptic plasticity of POMC neurons and ghrelin-induced food intake are also UCP2-dependent.","method":"UCP2 knockout mice, hypothalamic mitochondrial respiration assays, AMPK and CPT1 pharmacological inhibitors, electrophysiology of NPY/AgRP neurons, reactive oxygen species measurement, electron microscopy of mitochondria, synaptic plasticity assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — genetic KO plus pharmacological inhibition of pathway components, multiple orthogonal readouts (electrophysiology, ROS, mitochondrial morphology, behavior)","pmids":["18668043"],"is_preprint":false},{"year":2008,"finding":"A SNP (rs16147) in the NPY promoter region alters NPY expression in vitro and accounts for more than half of the in vivo variation in NPY mRNA levels driven by haplotype. Lower haplotype-driven NPY expression predicts higher amygdala activation to emotional stimuli and diminished stress resilience (reduced endogenous opioid neurotransmission during pain/stress). NPY haplotypes predict plasma NPY levels and lymphoblast NPY mRNA levels.","method":"Haplotype analysis, in vitro promoter-reporter assay (SNP rs16147), post-mortem brain NPY mRNA quantification, lymphoblast mRNA, plasma NPY RIA, fMRI amygdala activation, PET endogenous opioid neurotransmission","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro functional promoter assay plus convergent multi-level human phenotypic validation","pmids":["18385673"],"is_preprint":false},{"year":2008,"finding":"NPY promotes chemokinesis of dorsal root ganglion growth cones via an attractive turning response and increased growth rate mediated by the Y1 receptor, as demonstrated by asymmetric gradient application of NPY to cultured embryonic DRG neurons. Y1 receptor-deficient mice have fewer proliferating precursor cells and neuroblasts in the subventricular zone and rostral migratory stream and fewer neurons in the olfactory bulb, linking NPY-Y1 signaling to adult neurogenesis.","method":"Asymmetric NPY gradient application to embryonic DRG growth cone cultures (turning assay), Y1 and Y2 receptor knockout mouse analysis, SVZ/RMS BrdU proliferation assay, olfactory bulb neuron counting","journal":"Nutrition","confidence":"High","confidence_rationale":"Tier 2 — direct growth cone turning assay plus genetic KO model with quantitative neurogenesis readout","pmids":["18725084"],"is_preprint":false},{"year":2008,"finding":"Exogenous NPY Y2 receptor activation (NPY13-36, 300 nM) provides neuroprotection against AMPA-induced excitotoxicity in CA1 and CA3 pyramidal cells of mouse organotypic hippocampal slices, blocked by Y2 antagonist BIIE0246. Endogenous NPY provides additional neuroprotection revealed by Y1 antagonist (BIBP3226) or NPY-neutralizing antibody treatment. AMPA-induced neurodegeneration is associated with microglial BDNF release and upregulation of neuronal TrkB; this BDNF is not required for NPY Y2-mediated neuroprotection.","method":"Organotypic hippocampal slice culture, AMPA excitotoxicity model, propidium iodide uptake assay, selective Y1/Y2 receptor pharmacology, ELISA for BDNF, immunohistochemistry for TrkB and microglia","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological receptor dissection with quantitative cell death readout, mechanistic follow-up on BDNF pathway, single study","pmids":["18412629"],"is_preprint":false},{"year":2011,"finding":"NPY promotes SVZ cell proliferation (neuroproliferation) and chemokinesis in rats via Y1 receptor-mediated activation of the ERK1/2 MAP kinase pathway, as established by pharmacological approaches. NPY is endogenously synthesized by SVZ cells, suggesting autocrine/paracrine action. NPY does not affect self-renewal of SVZ stem cells.","method":"SVZ cell culture, BrdU proliferation assay, pharmacological Y1 receptor antagonism, ERK1/2 pathway inhibitors and Western blot, chemokinesis assay, endogenous NPY synthesis confirmed by RT-PCR/immunostaining","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection with multiple functional readouts, single lab","pmids":["21175616"],"is_preprint":false},{"year":2013,"finding":"NPY inhibits posttranslational processing of POMC to α-MSH by decreasing prohormone convertase-2 (PC2) expression in hypothalamic cells, mediated through Y1 receptors and the transcription factor Egr-1. Intra-PVN NPY also decreases PC2 in PVN samples, reducing pro-TRH processing. Additionally, NPY attenuates α-MSH-induced TRH production by (1) decreasing α-MSH-induced CREB phosphorylation, and (2) reducing α-MSH levels in the PVN.","method":"Hypothalamic cell culture and in vivo intra-PVN injection, PC2 protein/mRNA quantification, Egr-1 transcription factor analysis, CREB phosphorylation Western blot, α-MSH and TRH peptide measurements, Y1 receptor antagonist pharmacology","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro plus in vivo mechanistic dissection of NPY's regulation of POMC processing, single lab","pmids":["23321476"],"is_preprint":false},{"year":2016,"finding":"NPY promotes intestinal epithelial cell proliferation and reduces apoptosis via PI3K-β-catenin signaling and downregulation of miR-375. In NPY knockout mice, inflammation-induced tumorigenesis (DSS model) produces fewer and smaller polyps with reduced proliferation (PCNA, Ki67) and increased apoptosis (TUNEL) compared to wild-type. In vitro, NPY increases PCNA, β-catenin, c-Myc, and cyclin D1, and reduces p21 in epithelial cell lines. miR-375 inhibitor does not further enhance NPY-treated cells, indicating miR-375 acts downstream of NPY.","method":"NPY-/- knockout mice, DSS colitis-associated tumorigenesis model, intestinal epithelial cell lines (T84), PCNA/Ki67 IHC, TUNEL apoptosis assay, PI3K pathway inhibitors, β-catenin Western blot, miR-375 qRT-PCR, miR-375 inhibitor epistasis","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse model plus in vitro mechanistic pathway dissection, single lab","pmids":["27856419"],"is_preprint":false},{"year":2016,"finding":"Systemic NPY dose-dependently inhibits dural-evoked trigeminovascular neuronal firing in rat trigeminocervical complex (TCC) through Y1 receptor activation: the Y1 agonist reproduces NPY's inhibitory effect, while Y2 and Y5 agonists and the Y1 antagonist have no significant effect, establishing NPY as an antinociceptive peptide in the trigeminovascular system acting via Y1 receptors.","method":"In vivo electrophysiology in anesthetized rats (TCC neuronal recording), dural nociceptive stimulation, systemic NPY and receptor-selective agonist/antagonist administration","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo neurophysiology with pharmacological receptor dissection, single study","pmids":["27023421"],"is_preprint":false},{"year":2017,"finding":"Insulin signaling specifically in NPY neurons controls food intake and energy expenditure: genetic deletion of the insulin receptor in NPY neurons (in both flies and mice) leads to increased energy stores, obesity, dysregulation of the GH/IGF-1 axis, and altered insulin sensitivity. This establishes an ancient insulin/NPY neuronal network governing energy homeostasis across phyla.","method":"Conditional insulin receptor knockout specifically in NPY neurons (mouse and Drosophila), food intake and energy expenditure measurements, body composition analysis, GH/IGF-1 axis assessment, insulin sensitivity testing","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific conditional KO in two species with multiple metabolic phenotypes","pmids":["28580287"],"is_preprint":false},{"year":2021,"finding":"Ascending skeletal interoceptive signaling (via PGE2/EP4) downregulates hypothalamic NPY expression: EP4 activation induces SMILE (small heterodimer partner-interacting leucine zipper protein) in the hypothalamus, which binds pCREB as a transcriptional heterodimer on Npy promoters to inhibit NPY expression. Knockout of EP4 in sensory nerves increases NPY, causing bone catabolism and fat anabolism. Inhibition of NPY Y1R accelerates free fatty acid oxidation in osteoblasts and rescues bone loss.","method":"EP4 conditional KO in sensory neurons, hypothalamic SMILE expression, ChIP/co-IP showing SMILE-pCREB interaction at Npy promoter, NPY promoter reporter assay, Y1R antagonist treatment, osteoblast fatty acid oxidation assay, bone phenotype analysis","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO plus molecular promoter mechanism (SMILE-pCREB on Npy promoter), single study","pmids":["34468315"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of human Y1, Y2, and Y4 receptors in complex with NPY or pancreatic polypeptide and Gi1 protein reveal that the N-terminus of NPY forms extensive interactions specifically with Y1 but not with Y2 or Y4. Different receptors impose distinct binding poses on the peptide, reflecting conformational plasticity of NPY. Mutagenesis and functional studies confirmed subtype-specific receptor-peptide contacts, providing a structural basis for selective drug development.","method":"Cryo-EM structure determination, site-directed mutagenesis, functional signaling assays (cAMP, calcium), ligand binding assays","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures of three receptor subtypes plus mutagenesis and functional validation","pmids":["35507650"],"is_preprint":false}],"current_model":"NPY is a 36-amino acid peptide derived from proteolytic processing of a 97-aa preproNPY precursor; it is co-stored with noradrenaline in large dense-cored vesicles of sympathetic neurons and released preferentially at high firing frequencies. NPY signals through four Gi-coupled GPCRs (Y1, Y2, Y4, Y5) whose structures show subtype-specific peptide binding poses; Y1 and Y2 couple to inhibition of cAMP and elevation of intracellular Ca2+ in a cell-type-specific manner depending on available G proteins. In the hypothalamus, NPY/AgRP neurons receive excitatory ghrelin input (via PKA/N-type Ca2+ channel signaling and a UCP2-dependent mitochondrial fatty acid oxidation pathway) and inhibitory leptin input (via leptin receptors on NPY neurons that suppress NPY mRNA), with NPY promoting food intake primarily through Y1 receptors (dominant role established by KO mice) and modulating energy expenditure through Y5 receptors. NPY also suppresses POMC-to-α-MSH processing by reducing PC2 via Egr-1/Y1 receptor signaling, inhibits LH secretion via Y5 receptors, mediates antidepressant-like and anxiolytic effects via amygdala Y1 receptors, promotes adult neurogenesis and growth cone attraction via Y1/ERK1/2 signaling, provides neuroprotection against excitotoxicity via Y2 receptors, and exerts antinociceptive effects in the trigeminovascular system through Y1 receptors; brain NPY levels are inversely related to ethanol consumption as demonstrated by reciprocal NPY knockout and overexpression models."},"narrative":{"teleology":[{"year":1984,"claim":"Determining the full-length precursor structure of NPY was essential to understanding how the mature 36-amino acid peptide is generated; cDNA cloning from human pheochromocytoma revealed a 97-aa preproNPY processed at two sites into signal peptide, mature NPY, and a C-terminal peptide.","evidence":"cDNA cloning, nucleotide sequencing, in vitro translation with immunoprecipitation from human pheochromocytoma","pmids":["6589611"],"confidence":"High","gaps":["Processing enzymes responsible for cleavage were not identified","Functional role of the C-terminal peptide of NPY (CPON) remained unclear"]},{"year":1985,"claim":"How NPY is stored and released in sympathetic nerves was unknown; multiple studies established that NPY is co-stored with noradrenaline in large dense-cored vesicles, transported anterogradely, and acts as a co-transmitter producing vasoconstriction through a non-adrenergic receptor mechanism.","evidence":"Immunohistochemistry, RIA, pharmacological lesions (6-OHDA, reserpine), axonal ligation transport assay, local blood flow measurement with α-adrenoceptor blockade","pmids":["2858824","2866663"],"confidence":"High","gaps":["The molecular identity of the NPY receptor mediating vasoconstriction was unknown","Whether NPY release requires high-frequency versus tonic firing was not yet quantified"]},{"year":1986,"claim":"Understanding how NPY gene expression is controlled required knowledge of its genomic structure; the human NPY gene was mapped to four exons spanning ~8 kb, and ~530 bp of 5′ flanking sequence was shown to be sufficient for promoter activity in neuronal cells.","evidence":"Genomic library cloning, primer extension, reporter gene transfection assay in CA-77 and PC12 cells","pmids":["2427515"],"confidence":"High","gaps":["Transcription factor binding sites within the promoter were not functionally dissected","Tissue-specific regulatory elements beyond the proximal promoter were not identified"]},{"year":1990,"claim":"The rules governing frequency-dependent NPY release and its structure-activity relationships were established: NPY is preferentially released at high stimulation frequencies, auto-inhibits its own release, and requires an intact amidated C-terminus for receptor binding and cAMP inhibition.","evidence":"In vitro organ bath pharmacology, sympathetic nerve stimulation with overflow measurement, receptor binding, cAMP assays across multiple vascular beds","pmids":["2170253"],"confidence":"High","gaps":["Receptor subtypes mediating prejunctional feedback inhibition were not identified","Post-release metabolism/inactivation mechanisms for NPY were not addressed"]},{"year":1995,"claim":"The molecular identities and signaling properties of the principal NPY receptors were resolved: cloning of Y1 (Gi-coupled, cAMP inhibition, cell-type-dependent Ca²⁺ coupling), Y2 (preferring C-terminal NPY fragments), and Y4 (preferring pancreatic polypeptide) established the receptor family's pharmacological and signaling diversity.","evidence":"Expression cloning, heterologous expression in HEK-293 and CHO cells, radioligand binding, cAMP and intracellular Ca²⁺ assays, pertussis toxin sensitivity","pmids":["1321422","7592910","7559383","7493937"],"confidence":"High","gaps":["Y5 receptor had not yet been cloned","Structural basis for subtype-selective ligand recognition was unknown","Downstream effectors beyond cAMP/Ca²⁺ were not characterized"]},{"year":1998,"claim":"Whether endogenous NPY levels influence ethanol-related behavior was untested; reciprocal genetic models showed that NPY-knockout mice consume more ethanol with reduced sedative sensitivity, while NPY-overexpressing mice show the opposite, establishing an inverse NPY–ethanol relationship.","evidence":"NPY-/- knockout and neuronal NPY-overexpressing transgenic mice, two-bottle ethanol preference, ethanol-induced sleep test","pmids":["9845072"],"confidence":"High","gaps":["Which NPY receptor subtype mediates ethanol-related effects was not determined","Brain regional specificity of NPY's anti-ethanol effect was unknown"]},{"year":2000,"claim":"The receptor subtype hierarchy for NPY-induced feeding was disputed; Y1-knockout mice showed dramatically reduced NPY-induced feeding while Y5-knockout mice showed only partial attenuation, establishing Y1 as the dominant orexigenic receptor and Y5 as a modulator of energy expenditure and LH secretion.","evidence":"Y1-/- and Y5-/- knockout mice with ICV NPY/selective agonist administration, food intake measurement; separate studies with Y5 agonists measuring BAT temperature and oxygen consumption; Y5 pharmacology for LH suppression","pmids":["10698177","10564216","10465275"],"confidence":"High","gaps":["Whether Y1 and Y5 cooperate on the same neurons or distinct circuits was unclear","Compensatory receptor upregulation in KO models was not assessed"]},{"year":2001,"claim":"The hierarchical relationship between ghrelin, leptin, and NPY in hypothalamic feeding circuits was unknown; ghrelin was shown to activate Fos in NPY/AgRP neurons and require intact NPY/AgRP signaling for its orexigenic effect, while leptin suppresses fasting-induced NPY mRNA via its receptor on arcuate neurons.","evidence":"ICV ghrelin with Fos IHC, anti-NPY/AgRP antibody neutralization, NPY mRNA RT-PCR; leptin infusion in fasted rats and leptin-receptor-mutant models with NPY mRNA quantification","pmids":["11196643","11737554"],"confidence":"High","gaps":["Direct electrophysiological confirmation of ghrelin-to-NPY neuron activation was pending","Intracellular signaling cascade from ghrelin receptor to NPY transcription was unresolved"]},{"year":2003,"claim":"How ghrelin signal transduction reaches NPY neurons at the single-cell level was resolved: ghrelin directly elevates [Ca²⁺]i in NPY-immunopositive arcuate neurons via PKA and N-type Ca²⁺ channels, with leptin acting as a direct antagonist of this response.","evidence":"Enzymatic dissociation of rat arcuate neurons, fura-2 Ca²⁺ imaging, NPY immunocytochemistry, PKA/PKC inhibitors, N-type/L-type channel blockers","pmids":["12663466"],"confidence":"High","gaps":["Whether ghrelin modulates NPY vesicular release in addition to excitability was untested","Downstream transcriptional consequences of the PKA/Ca²⁺ cascade in NPY neurons were not mapped"]},{"year":2008,"claim":"Multiple mechanistic advances converged: (1) ghrelin activation of NPY/AgRP neurons requires UCP2-dependent mitochondrial fatty acid oxidation via AMPK/CPT1; (2) an NPY promoter SNP (rs16147) accounts for >50% of in vivo NPY expression variation and predicts amygdala stress reactivity; (3) NPY-Y1 signaling drives adult neurogenesis via ERK1/2 and neuroprotection occurs via Y2 receptors; (4) subtype-specific receptor–peptide contacts were mapped showing the NPY N-terminus engages Y1 but not Y2/Y4.","evidence":"UCP2-KO mice with electrophysiology and mitochondrial assays; haplotype-promoter-reporter assays with fMRI and PET imaging; Y1-KO SVZ neurogenesis quantification and growth cone turning assays; receptor mutagenesis/chimera binding studies","pmids":["18668043","18385673","18725084","18412629","18725086"],"confidence":"High","gaps":["The full mitochondrial signaling pathway from UCP2 to membrane depolarization in NPY neurons was incompletely characterized","Whether the rs16147 promoter variant affects NPY levels in specific brain nuclei was unresolved","Structural resolution of receptor–peptide complexes at atomic level was still lacking"]},{"year":2013,"claim":"How NPY antagonizes the melanocortin system at a post-translational level was unknown; NPY was shown to suppress prohormone convertase-2 (PC2) expression via Y1/Egr-1 signaling, thereby reducing POMC-to-α-MSH processing and α-MSH-induced CREB phosphorylation in hypothalamic neurons.","evidence":"Hypothalamic cell culture and in vivo intra-PVN NPY injection, PC2 mRNA/protein quantification, Egr-1 analysis, CREB phosphorylation Western blot, Y1 antagonist pharmacology","pmids":["23321476"],"confidence":"Medium","gaps":["Whether this mechanism operates in the arcuate nucleus or only in PVN was unclear","The contribution of PC2 suppression versus direct synaptic inhibition to NPY's net anti-melanocortin effect was not quantified"]},{"year":2017,"claim":"Whether insulin acts directly on NPY neurons to regulate energy balance was untested; conditional deletion of the insulin receptor specifically in NPY neurons in both mice and Drosophila produced obesity and altered GH/IGF-1 signaling, establishing an evolutionarily conserved insulin–NPY neuronal axis.","evidence":"Conditional insulin receptor knockout in NPY neurons (mouse and Drosophila), metabolic phenotyping including body composition, food intake, energy expenditure, GH/IGF-1 axis assessment","pmids":["28580287"],"confidence":"High","gaps":["Whether insulin directly regulates NPY transcription or only neuronal excitability was not distinguished","Interaction between insulin and leptin/ghrelin signaling within NPY neurons was not addressed"]},{"year":2021,"claim":"A peripheral-to-central regulatory loop for NPY was discovered: skeletal PGE2/EP4 signaling induces the co-repressor SMILE in the hypothalamus, which binds pCREB on the Npy promoter to suppress NPY transcription, linking bone-derived interoception to hypothalamic NPY control of bone and fat metabolism.","evidence":"EP4 conditional KO in sensory neurons, ChIP and co-IP for SMILE–pCREB on Npy promoter, NPY promoter reporter, Y1R antagonist rescue of bone phenotype, osteoblast fatty acid oxidation assay","pmids":["34468315"],"confidence":"Medium","gaps":["Whether SMILE–pCREB interaction on the Npy promoter operates in all hypothalamic nuclei or is regionally restricted is unknown","Independent replication of the skeletal interoceptive pathway is lacking"]},{"year":2022,"claim":"Atomic-resolution understanding of NPY–receptor recognition was achieved: cryo-EM structures of Y1, Y2, and Y4 in complex with NPY/PP and Gi1 confirmed that the NPY N-terminus makes extensive contacts with Y1 but not Y2/Y4, providing the structural basis for subtype-selective pharmacology.","evidence":"Cryo-EM structure determination of three receptor–ligand–Gi complexes, site-directed mutagenesis, cAMP and Ca²⁺ functional assays","pmids":["35507650"],"confidence":"High","gaps":["Y5 receptor structure in complex with NPY has not been determined","Conformational dynamics of NPY upon receptor binding are not captured by static cryo-EM","Structure-guided selective agonist/antagonist design has not yet been validated in vivo"]},{"year":null,"claim":"Key unresolved questions include the structural basis of Y5 receptor selectivity, the circuit-level integration of insulin/leptin/ghrelin inputs onto individual NPY neurons, the precise mechanism by which UCP2-dependent mitochondrial changes translate to NPY neuronal firing, and whether NPY's peripheral metabolic effects on adipocytes and bone are therapeutically targetable.","evidence":"","pmids":[],"confidence":"Low","gaps":["No Y5 receptor structure available","Single-cell resolution of convergent hormonal inputs on NPY neurons is lacking","In vivo therapeutic validation of NPY-receptor-selective compounds for metabolic or psychiatric indications is absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[5,6,7,15,24,35]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13,14,30]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[3,5]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,5,15]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7,8,15,24,35]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[12,20,21,25,26,28]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,30]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[23]}],"complexes":[],"partners":["NPY1R","NPY2R","NPY5R","NPY4R","GHSR","LEPR","UCP2"],"other_free_text":[]},"mechanistic_narrative":"NPY is a 36-amino acid neuropeptide processed from a 97-amino acid precursor (preproNPY) that functions as a co-transmitter with noradrenaline in sympathetic neurons and as a major hypothalamic regulator of energy homeostasis, neuroendocrine function, and stress-related behavior [PMID:6589611, PMID:2858824, PMID:2170253]. NPY signals through Gi-coupled Y1, Y2, Y4, and Y5 receptors with subtype-specific binding poses — cryo-EM structures reveal that the NPY N-terminus engages Y1 but not Y2/Y4 — and couples to inhibition of cAMP and elevation of intracellular Ca²⁺ in a cell-type-dependent manner [PMID:1321422, PMID:7592910, PMID:35507650]. In the hypothalamus, NPY neurons integrate excitatory ghrelin input (via PKA/N-type Ca²⁺ channels and a UCP2-dependent mitochondrial fatty acid oxidation pathway) and inhibitory leptin input to drive feeding primarily through Y1 receptors — as established by Y1-knockout mice showing dramatically reduced NPY-induced food intake — while Y5 receptors mediate reductions in energy expenditure and suppression of LH secretion [PMID:18668043, PMID:11737554, PMID:10698177, PMID:10465275, PMID:12697685]. Beyond energy balance, NPY exerts Y1-mediated antidepressant-like and anxiolytic effects, promotes adult neurogenesis via Y1/ERK1/2 signaling, provides Y2 receptor-dependent neuroprotection against excitotoxicity, suppresses POMC-to-α-MSH processing through Y1/Egr-1-mediated downregulation of PC2, and modulates ethanol consumption as demonstrated by reciprocal knockout and overexpression models [PMID:11927186, PMID:21175616, PMID:18412629, PMID:23321476, PMID:9845072]."},"prefetch_data":{"uniprot":{"accession":"P01303","full_name":"Pro-neuropeptide Y","aliases":[],"length_aa":97,"mass_kda":10.9,"function":"NPY is implicated in the control of feeding and in secretion of gonadotrophin-release hormone","subcellular_location":"Secreted; Cytoplasmic vesicle, secretory vesicle, neuronal dense core vesicle","url":"https://www.uniprot.org/uniprotkb/P01303/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NPY","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NPY","total_profiled":1310},"omim":[{"mim_id":"621441","title":"SPERMATOGENESIS-ASSOCIATED PROTEIN 32; SPATA32","url":"https://www.omim.org/entry/621441"},{"mim_id":"617869","title":"NK1 HOMEOBOX 1; NKX1-1","url":"https://www.omim.org/entry/617869"},{"mim_id":"617002","title":"BICD FAMILY-LIKE CARGO ADAPTOR 1; BICDL1","url":"https://www.omim.org/entry/617002"},{"mim_id":"616584","title":"SPERMATOGENESIS-ASSOCIATED PROTEIN 31, SUBFAMILY A, MEMBER 7; SPATA31A7","url":"https://www.omim.org/entry/616584"},{"mim_id":"615852","title":"RAS-ASSOCIATED PROTEIN RAB6B; RAB6B","url":"https://www.omim.org/entry/615852"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adrenal gland","ntpm":115.4},{"tissue":"brain","ntpm":297.4},{"tissue":"prostate","ntpm":348.0}],"url":"https://www.proteinatlas.org/search/NPY"},"hgnc":{"alias_symbol":["PYY4"],"prev_symbol":[]},"alphafold":{"accession":"P01303","domains":[{"cath_id":"1.20.5","chopping":"31-63","consensus_level":"medium","plddt":86.7309,"start":31,"end":63}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P01303","model_url":"https://alphafold.ebi.ac.uk/files/AF-P01303-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P01303-F1-predicted_aligned_error_v6.png","plddt_mean":75.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NPY","jax_strain_url":"https://www.jax.org/strain/search?query=NPY"},"sequence":{"accession":"P01303","fasta_url":"https://rest.uniprot.org/uniprotkb/P01303.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P01303/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P01303"}},"corpus_meta":[{"pmid":"18668043","id":"PMC_18668043","title":"UCP2 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fatty acid oxidation through an AMPK–CPT1 pathway that generates free radicals, which are scavenged by UCP2, leading to mitochondrial proliferation and electrical activation of NPY/AgRP neurons, and driving food intake.\",\n      \"method\": \"Genetic KO of UCP2 in mice, mitochondrial respiration assays, electrophysiology of NPY/AgRP neurons, synaptic plasticity measurements, pharmacological AMPK/CPT1 manipulation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (KO, in vivo respiration, electrophysiology, behavioral assay) in a single high-impact study\",\n      \"pmids\": [\"18668043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM/crystal structures of human Y1, Y2, and Y4 receptors complexed with NPY or pancreatic polypeptide and Gi1 protein reveal that the NPY N-terminus forms extensive interactions with Y1 but not Y2/Y4, and that a conserved aspartate in the third extracellular loop is essential for ligand binding across all Y receptors; receptor-subtype-specific contacts were validated by mutagenesis and functional assays.\",\n      \"method\": \"Cryo-EM and crystal structure determination, receptor mutagenesis, functional binding and signaling assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution structures with mutagenesis and functional validation in one study\",\n      \"pmids\": [\"35507650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A promoter SNP (rs16147) in the NPY gene alters NPY expression in vitro and accounts for more than half of the haplotype-driven variation in NPY mRNA levels in post-mortem brain and plasma; lower NPY expression predicts higher amygdala activation to emotional stimuli and reduced resilience to stress.\",\n      \"method\": \"In vitro promoter-reporter assay, post-mortem brain mRNA quantification, lymphoblast NPY mRNA, plasma NPY measurement, fMRI with emotional stimuli, pain/stress-induced opioid neurotransmission PET\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple convergent methods across human tissues and functional brain imaging, replicated across phenotypic levels\",\n      \"pmids\": [\"18385673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NPY produces antidepressant-like activity in the mouse forced swimming test through the Y1 receptor subtype: Y1 agonist [Leu31,Pro34]PYY mimicked NPY, Y2 agonist did not, and Y1 antagonists BIBO3304/BIBP3226 blocked NPY's anti-immobility effect; Y2 antagonist BIIE0246 also reduced immobility, likely by potentiating endogenous NPY release.\",\n      \"method\": \"Intracerebroventricular injections of receptor-selective agonists and antagonists in mouse forced swimming test; open field locomotion controls\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with selective agonists/antagonists, but single lab\",\n      \"pmids\": [\"11927186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The NPY Y5 receptor subtype predominantly mediates NPY-induced inhibition of LH secretion: selective Y5 agonists (PYY3-36, human PP) inhibited LH with similar potency to NPY, Y2 and Y4 selective agonists had no effect, and a non-peptidic Y5 antagonist blocked the NPY-induced LH inhibition.\",\n      \"method\": \"Intracerebroventricular injection of receptor-selective NPY analogs in castrated rats, plasma LH radioimmunoassay, receptor binding displacement assays\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with multiple selective ligands and receptor antagonist; single lab\",\n      \"pmids\": [\"10465275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The NPY Y5 receptor mediates both NPY-stimulated food intake and suppression of energy expenditure/thermogenesis: ICV administration of Y5-selective agonist D-[Trp32]-NPY reduced brown adipose tissue temperature, oxygen consumption, and energy expenditure, mimicking full NPY; Y1, Y2, and Y4 agonists did not replicate these effects.\",\n      \"method\": \"ICV infusion of receptor-selective NPY analogs, implanted temperature transponders in BAT, indirect calorimetry in rats\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological selectivity demonstrated with multiple receptor agonists and metabolic readouts\",\n      \"pmids\": [\"10564216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Insulin signaling specifically within NPY neurons controls food intake and energy expenditure: conditional knockout of the insulin receptor in NPY neurons in both Drosophila and mice led to increased food intake, increased energy stores, obesity, dysregulation of the GH/IGF-1 axis, and altered insulin sensitivity.\",\n      \"method\": \"NPY neuron-specific insulin receptor knockout in mice and flies, metabolic phenotyping, energy expenditure measurement\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KO with defined metabolic phenotype, replicated across two species\",\n      \"pmids\": [\"28580287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NPY inhibits posttranslational processing of POMC to α-MSH by decreasing prohormone convertase-2 (PC2) expression via NPY Y1 receptor and Egr-1; NPY also reduces α-MSH-induced CREB phosphorylation and decreases α-MSH levels in the PVN, thereby suppressing TRH production.\",\n      \"method\": \"Intra-PVN NPY administration in rats, PC2 protein and mRNA quantification, Egr-1 knockdown, CREB phosphorylation assay, α-MSH and TRH measurements\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway dissection with receptor antagonists, signaling assays, and knockdown; single lab\",\n      \"pmids\": [\"23321476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NPY promotes chemokinesis and neurogenesis in the rat subventricular zone via Y1 receptor-mediated activation of the ERK1/2 MAP kinase pathway; NPY is endogenously synthesized within the SVZ, suggesting autocrine/paracrine action.\",\n      \"method\": \"SVZ cell culture, pharmacological Y1 receptor blockade, ERK1/2 phosphorylation assays, BrdU proliferation assays, endogenous NPY synthesis confirmed by immunostaining\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological receptor identification combined with signaling pathway assay; single lab\",\n      \"pmids\": [\"21175616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NPY provides neuroprotection against AMPA-induced excitotoxicity in hippocampal slice cultures via Y2 receptor activation; endogenous NPY also contributes to protection via Y1 receptors in CA1; the neuroprotection was partially linked to BDNF released from microglia at injury sites.\",\n      \"method\": \"Organotypic hippocampal slice cultures, AMPA excitotoxicity model, propidium iodide uptake, selective Y1/Y2 receptor agonists and antagonists, neutralizing antibodies, BDNF ELISA, immunohistochemistry\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological tools and endpoint measures; single lab\",\n      \"pmids\": [\"18412629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NPY dose-dependently inhibits trigeminocervical complex neuronal firing in response to dural nociceptive stimulation through NPY Y1 receptor activation, as demonstrated by Y1 agonist mimicry and Y1 antagonist blockade in an in vivo rat electrophysiology migraine model.\",\n      \"method\": \"In vivo electrophysiology in anesthetized rats, dural electrical stimulation, systemic NPY and receptor-selective agonist/antagonist administration\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo electrophysiology with pharmacological receptor dissection; single lab\",\n      \"pmids\": [\"27023421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"NPY coexists with noradrenaline in large dense-cored vesicles of sympathetic neurons and is preferentially released during high-frequency stimulation or strong reflex sympathetic activation; NPY release is inhibited by prejunctional α2-adrenoceptors and adenosine receptors, and facilitated by angiotensin II or β-receptor activation; NPY exerts prejunctional inhibitory effects on both NA and NPY release and potentiates NA-evoked vasoconstriction.\",\n      \"method\": \"Pharmacological stimulation/inhibition studies of peripheral sympathetic nerves, overflow measurements, vascular contraction assays, frequency-dependent stimulation protocols\",\n      \"journal\": \"Fundamental & clinical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — extensive pharmacological characterization with multiple manipulations replicated across vascular beds; foundational cotransmission mechanism\",\n      \"pmids\": [\"2170253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"NPY is co-localized with noradrenaline in sympathetic perivascular nerves in dental pulp and oral mucosa; sympathetic stimulation produces vasoconstriction that is partially resistant to phentolamine (α-blocker) but abolished by guanethidine, while NPY-induced vasoconstriction is unaffected by phentolamine or guanethidine, indicating NPY acts as an independent sympathetic vasoconstrictor co-transmitter.\",\n      \"method\": \"Immunohistochemistry, retrograde axonal ligation, HPLC of NPY-like immunoreactivity, in vivo local blood flow measurement with 125I clearance, pharmacological adrenoceptor blockade\",\n      \"journal\": \"Acta physiologica Scandinavica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct colocalization plus functional pharmacological dissection of sympathetic cotransmission; foundational study\",\n      \"pmids\": [\"2866663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"NPY suppresses experimental autoimmune encephalomyelitis via Y1 receptors: Y1 agonists inhibited EAE induction and shifted autoreactive T cells toward a Th2 phenotype; Y1 antagonist treatment accelerated EAE onset; ex vivo analysis confirmed direct Y1-mediated suppression of MOG-specific Th1 responses in autoreactive T cells.\",\n      \"method\": \"Active EAE model in C57BL/6 mice, Y1 and Y5 receptor agonist/antagonist treatment, ex vivo T cell cytokine assays, Y1 antagonist-induced EAE acceleration\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function and gain-of-function pharmacological approach with defined cellular phenotype; single lab\",\n      \"pmids\": [\"14500640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"NPY Y1 receptors in human adipocytes mediate antilipolytic effects and stimulate leptin secretion: RT-PCR confirmed Y1 (plus Y4, Y5) receptor transcripts; binding studies showed high-affinity Y1-type sites; selective Y1 antagonists SR120819A and BIBP3226 fully blocked NPY-induced antilipolysis and leptin secretion enhancement.\",\n      \"method\": \"RT-PCR, radioligand binding, [35S]GTPγS functional assay, lipolysis assay in isolated human adipocytes, leptin secretion measurement, selective Y1 antagonists\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular identification of receptor plus functional pharmacological dissection in primary human cells; single lab\",\n      \"pmids\": [\"10858507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"NPY undergoes anterograde axonal transport in sympathetic neurons at ~3 mm/h; reserpine depletes NPY from peripheral nerve terminals (dependent on intact nerve activity) while NPY accumulates in ganglia, whereas 6-OHDA depletes NPY in terminal regions with ganglionic accumulation; reserpine increases axonal transport of NPY, and NPY synthesis in ganglia is regulated by nicotinic receptor activity.\",\n      \"method\": \"Sciatic nerve ligation with accumulated immunoreactivity quantification, 6-OHDA and reserpine pretreatment, HPLC of NPY-LI, immunohistochemistry\",\n      \"journal\": \"Naunyn-Schmiedeberg's archives of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct nerve ligation and pharmacological manipulation with quantitative NPY measurement; foundational transport study\",\n      \"pmids\": [\"2858824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NPY activates Y1 receptors on pulmonary arterial smooth muscle cells to acutely increase intracellular calcium, enhance vasoconstriction (additively with adrenaline), and stimulate proliferation via p38 and PKD signaling pathways; Y1 receptor expression is upregulated in pulmonary hypertension patients and rodent PH models.\",\n      \"method\": \"Calcium imaging, wire myography, thymidine incorporation proliferation assay, Western blotting for p38/PKD, selective Y1 antagonist BIBO 3304, quantitative PCR, immunofluorescence in patient samples\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal cellular assays with receptor-selective antagonist; single lab\",\n      \"pmids\": [\"24779394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ascending skeletal interoceptive signaling (via PGE2/EP4) downregulates hypothalamic NPY expression by inducing SMILE protein, which binds pCREB on the Npy promoter to inhibit transcription; reduced NPY leads to lipolysis of free fatty acids in adipose tissue, providing substrate for osteoblastic bone formation; EP4 knockout in sensory nerves increases NPY causing bone catabolism and fat anabolism, reversed by Y1R inhibition.\",\n      \"method\": \"Conditional EP4 knockout in sensory neurons, hypothalamic SMILE knockin/knockout, chromatin immunoprecipitation on Npy promoter, fatty acid oxidation assays in osteoblasts, bone histomorphometry\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and molecular mechanistic dissection with defined bone/fat phenotype; single lab\",\n      \"pmids\": [\"34468315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Chronic consumption of sucralose (sweet/energy imbalance) activates an NPY-dependent neuronal fasting response that increases food intake in mammals; the effect was NPY-dependent as it was abolished in NPY knockout conditions.\",\n      \"method\": \"Long-term sucralose diet in flies and mice, NPY knockout mice, behavioral food intake measurement, genetic epistasis with NPY/NPF pathway\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function (NPY KO) with defined behavioral phenotype replicated across species\",\n      \"pmids\": [\"27411010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Centrally administered NPY inhibits gastric emptying and intestinal transit via a beta-adrenergic pathway: intracisternal NPY suppressed solid and liquid meal transit; propranolol antagonized this effect while phentolamine did not; carbachol blocked NPY effects but atropine and hexamethonium did not.\",\n      \"method\": \"Intracisternal NPY injection in conscious rats, gastric emptying and intestinal transit measurement, pharmacological adrenergic/cholinergic blockade\",\n      \"journal\": \"Digestive diseases and sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic pharmacological dissection of pathway; single lab\",\n      \"pmids\": [\"8482183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"NPY hypothermia and NPY-induced feeding in the rat ventromedial hypothalamus are mediated by Y1 receptors: antisense oligodeoxynucleotides against NPY-Y1R suppressed NPY-induced feeding and caused hyperthermia/hypophagia; mismatched controls had no effect.\",\n      \"method\": \"Bilateral VMH microinjection of antisense oligodeoxynucleotides targeting Y1 receptor, body temperature telemetry, food intake measurement in unrestrained rats\",\n      \"journal\": \"Proceedings. Biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — antisense knockdown with defined physiological endpoints; single lab\",\n      \"pmids\": [\"8760491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"Synthetic porcine NPY adopts a concentration-independent α-helical conformation in aqueous solution (as shown by circular dichroism), forms neither wholly monomeric nor dimeric species (sedimentation equilibria), and binds its receptor with IC50 of ~5 nM, consistent with an intramolecularly stabilized helical structure.\",\n      \"method\": \"Solid-phase peptide synthesis, HPLC purification, circular dichroism spectroscopy, sedimentation equilibria, radioligand receptor binding assay\",\n      \"journal\": \"Neuropeptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biophysical characterization with functional receptor binding; single lab\",\n      \"pmids\": [\"2823169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NPY axon guidance: NPY elicits an attractive turning response and increases growth rate of embryonic DRG growth cones via Y1 receptor; Y1 and Y2 receptors are expressed in neuroblasts of the SVZ/rostral migratory stream, and Y1 or Y2 receptor KO mice have fewer proliferating precursors and fewer olfactory bulb interneurons.\",\n      \"method\": \"Embryonic DRG growth cone turning assay with asymmetric NPY gradients, Y1/Y2 receptor KO mouse neurogenesis analysis, immunohistochemistry for neuroblast markers\",\n      \"journal\": \"Nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct growth cone turning assay plus KO neurogenesis phenotype; single lab\",\n      \"pmids\": [\"18725084\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NPY is a 36-amino acid neuropeptide that adopts an α-helical conformation, is co-stored with noradrenaline in large dense-cored vesicles of sympathetic neurons and released preferentially by high-frequency stimulation, and acts through four G protein-coupled Y receptors (Y1–Y5 in humans) coupled to Gi to inhibit cAMP, regulate intracellular calcium, and modulate ERK/p38/PKD signaling; centrally, NPY/AgRP neurons in the arcuate nucleus are activated by ghrelin via a UCP2-dependent mitochondrial fatty acid oxidation pathway and are inhibited by leptin and insulin signaling, driving food intake primarily through Y1 and Y5 receptors and suppressing anorexigenic peptide output by reducing POMC processing (via PC2/Egr-1) and TRH production; peripherally, NPY acts via Y1 receptors to produce vasoconstriction, stimulate smooth muscle cell proliferation, exert antilipolytic and leptin-secretory effects in adipocytes, inhibit trigeminovascular pain transmission, suppress autoreactive Th1 responses in the immune system, and promote neurogenesis and axon guidance through Y1-ERK signaling.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract mechanistic discoveries from KEEP papers only.\n\n**Classification notes:**\n- Papers [2] from additional list (MGC cDNA sequencing), [3] HuRI interactome, [4] GO propagation, [5] MGC, [15] MDD GWAS, [16] liver interactome, [18] chr7 sequence, [19] periodontitis GWAS, [20] diabetic retinopathy GWAS, [21] lipids GWAS, [22] coeliac GWAS, [23] chr7 sequence, [25] cannabis/psychosis, [26] alcohol genomics, [27] NPY methylation in CRC (epigenetic biomarker), [28] NPY Leu7Pro/alcohol association, [29] CNV/ADHD, are largely GWAS/genomic/association studies — EXCLUDE (no mechanistic findings about NPY protein).\n- Papers about NPY expression correlations, IHC distributions only → EXCLUDE from discoveries.\n- KEEP: papers with direct mechanistic experiments about NPY protein function, receptor coupling, signaling pathways, structure, etc.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1984,\n      \"finding\": \"The human NPY gene encodes a 97-amino acid precursor (preproNPY) that undergoes proteolytic processing at two sites to generate three peptides: a 28-aa signal peptide, the 36-aa mature NPY, and a 30-aa C-terminal peptide. The coding sequence was determined from a human pheochromocytoma cDNA.\",\n      \"method\": \"cDNA cloning, nucleotide sequencing, in vitro translation with immunoprecipitation, Edman degradation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct sequencing plus biochemical validation of precursor structure\",\n      \"pmids\": [\"6589611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The human NPY gene spans ~8 kb and contains four exons: exon 1 is non-translated; exon 2 encodes the signal peptide through residue 63 of preproNPY; exon 3 encodes 27 amino acids; exon 4 encodes the C-terminal heptapeptide and 3′ UTR. A TATA-like and CAAT-like sequence are present 25 and 70 bp upstream of the transcription start site, respectively. Approximately 530 bp of 5′ flanking sequence is sufficient for promoter activity in neuronal cell lines (CA-77, PC12).\",\n      \"method\": \"Genomic library cloning, primer extension, reporter gene (chloramphenicol acetyltransferase) transfection assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — gene structure determined by sequencing plus functional promoter assay\",\n      \"pmids\": [\"2427515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"Synthetic porcine NPY adopts a concentration-independent alpha-helical conformation in aqueous solution at neutral/basic pH (as shown by circular dichroism), with loss of helical content at acidic pH. The peptide is neither wholly monomeric nor dimeric by sedimentation equilibrium, suggesting an intramolecularly stabilized helical structure analogous to avian pancreatic polypeptide. Receptor binding affinity IC50 ~5 nM.\",\n      \"method\": \"Solid-phase peptide synthesis, circular dichroism spectroscopy, sedimentation equilibrium, radioligand receptor binding assay\",\n      \"journal\": \"Neuropeptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — biophysical characterization of synthetic peptide, single study\",\n      \"pmids\": [\"2823169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"NPY is co-localized with noradrenaline in large dense-cored vesicles of sympathetic perivascular neurons. 6-OHDA treatment depletes NPY-immunoreactivity in terminal regions while increasing it in stellate ganglion cell bodies. Reserpine causes dose- and time-dependent depletion of NPY from sympathetic nerve terminals (heart, spleen) dependent on intact nerve activity, but unlike NA, NPY depletion by reserpine is entirely dependent on ongoing neuronal activity. Axonal ligation reveals anterograde axonal transport of NPY at ~3 mm/h, and reserpine significantly increases this transport rate.\",\n      \"method\": \"Immunohistochemistry, radioimmunoassay, 6-OHDA and reserpine pharmacological lesions, nerve ligation axonal transport assay, HPLC\",\n      \"journal\": \"Naunyn-Schmiedeberg's archives of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (IHC, RIA, pharmacological manipulation, ligation assay) replicated across tissues\",\n      \"pmids\": [\"2858824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"NPY is present in sympathetic perivascular nerves of dental pulp and oral mucosa (co-localized with noradrenaline) and produces potent, long-lasting vasoconstriction resistant to alpha-adrenoceptor blockade by phentolamine and unaffected by guanethidine, demonstrating that NPY acts through a receptor mechanism distinct from adrenoceptors to reduce local blood flow.\",\n      \"method\": \"Immunohistochemistry, retrograde axonal tracing, HPLC, local 125I-clearance blood flow measurement, pharmacological antagonism (phentolamine, guanethidine)\",\n      \"journal\": \"Acta physiologica Scandinavica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional vascular assay with pharmacological dissection, multiple tissues\",\n      \"pmids\": [\"2866663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"NPY co-exists with noradrenaline in large dense-cored vesicles and is preferentially released compared to NA upon high-frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited by prejunctional alpha-2 adrenoceptors and adenosine receptors, and facilitated by angiotensin II or beta-receptor activation. NPY itself exerts prejunctional inhibition of both NA and NPY release. A large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cAMP formation, and vasoconstrictor effects. Reserpine-induced NPY synthesis in ganglia is regulated by nicotinic receptor activity.\",\n      \"method\": \"In vitro organ bath pharmacology, sympathetic nerve stimulation, radioimmunoassay of overflow, receptor binding, cAMP assay, pharmacological dissection\",\n      \"journal\": \"Fundamental & clinical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple functional assays establishing co-transmission mechanism and structure-activity relationships, replicated across vascular beds\",\n      \"pmids\": [\"2170253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The cloned human NPY Y1 receptor is a G protein-coupled receptor that, when expressed in HEK-293 cells, couples to a pertussis toxin-sensitive Gi protein to inhibit cAMP accumulation. In CHO cells, the same receptor couples instead to elevation of intracellular calcium, demonstrating cell-type-specific second messenger coupling dependent on the available G protein repertoire.\",\n      \"method\": \"cDNA cloning, heterologous expression in CHO and HEK-293 cells, radioligand binding, cAMP assay, intracellular calcium measurement, pertussis toxin treatment\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in two cell systems with pharmacological and biochemical validation\",\n      \"pmids\": [\"1321422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The cloned human NPY Y2 receptor (381 aa, 31% identical to Y1) expressed in HEK-293 and CHO cells binds NPY and PYY with high affinity but binds [Leu31,Pro34]NPY with low affinity, and binds truncated NPY13-36 with high affinity — confirming Y2 pharmacological profile. The Y2 receptor inhibits forskolin-stimulated cAMP and increases intracellular Ca2+ when stably expressed in CHO cells.\",\n      \"method\": \"Expression cloning from hippocampal cDNA library, radioligand binding (125I-PYY), cAMP assay, intracellular calcium measurement in stably transfected CHO cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — expression cloning plus functional characterization in two independent reports (PMIDs 7592910 and 7559383)\",\n      \"pmids\": [\"7592910\", \"7559383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"A novel human NPY receptor (PP1/Y4) with 43% amino acid identity to Y1 was cloned; it binds pancreatic polypeptide with highest affinity (Ki 13.8 pM), PYY with 1.44 nM, and NPY with 9.9 nM — pharmacologically distinguishing it from Y1 and Y2. In stably transfected CHO cells, this receptor inhibits forskolin-stimulated cAMP synthesis via Gi.\",\n      \"method\": \"Homology-based cloning from human cDNA, radioligand binding, cAMP assay in stably transfected CHO cells, Northern blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cloning plus pharmacological and functional characterization\",\n      \"pmids\": [\"7493937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Leptin receptor mRNA co-distributes with NPY-expressing neurons in the ventromedial subdivision of the hypothalamic arcuate nucleus, demonstrated by in situ hybridization of semi-adjacent sections, establishing that leptin receptors are expressed on NPY neurons.\",\n      \"method\": \"In situ hybridization on mouse brain sections with probes for leptin receptor mRNA and NPY mRNA on semi-adjacent sections\",\n      \"journal\": \"Neuroreport\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-distribution by ISH, single study, anatomical co-localization without direct functional coupling\",\n      \"pmids\": [\"9116246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Antisense oligodeoxynucleotides targeting the NPY Y1 receptor mRNA, microinjected into the rat ventromedial hypothalamus, suppress NPY-induced feeding and cause hypothermia and body weight reduction, establishing that Y1 receptors in the VMH are necessary for NPY-induced feeding and thermoregulatory responses.\",\n      \"method\": \"Antisense oligodeoxynucleotide knockdown of Y1R in VMH, food intake measurement, body temperature telemetry, locomotor activity monitoring\",\n      \"journal\": \"Proceedings. Biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific phenotypic readout, single study\",\n      \"pmids\": [\"8760491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"NPY acting on Y2 receptors in the dorsal vagal complex (DVC) mimics PYY's suppression of TRH-stimulated gastric motility, while Y1 receptor activation in the DVC stimulates gastric motility from basal conditions. The direction of NPY's effect on gastric motility depends on which receptor subtype is activated and the basal state of stimulation.\",\n      \"method\": \"Microinjection of selective Y1 and Y2 agonists/antagonists into rat DVC, in vivo gastric motility recording, pharmacological dissection\",\n      \"journal\": \"Neurogastroenterology and motility\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — selective agonist/antagonist pharmacology with direct physiological readout\",\n      \"pmids\": [\"9198086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"NPY-deficient mice (preproNPY knockout) show increased ethanol consumption and reduced sensitivity to the sedative/hypnotic effects of ethanol (faster recovery from ethanol-induced sleep at equivalent plasma ethanol levels). Conversely, transgenic mice overexpressing NPY in neurons show lower ethanol preference and enhanced sedative sensitivity. These results establish an inverse relationship between brain NPY levels and ethanol consumption/resistance.\",\n      \"method\": \"Targeted gene disruption (NPY-/- mice), transgenic NPY overexpression, two-bottle choice ethanol consumption assay, ethanol-induced sleep/loss-of-righting-reflex test, plasma ethanol measurement\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic manipulation (KO and OE) with clear behavioral phenotype, replicated across genotypes\",\n      \"pmids\": [\"9845072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The inhibitory effect of centrally administered NPY on LH secretion is predominantly mediated by the Y5 receptor subtype: selective Y5 agonists (PYY3-36, human PP, [D-Trp32]NPY) inhibited LH release, while selective Y2 and Y4 agonists did not. A non-peptidic Y5 receptor antagonist (icv, 6–100 μg) dose-dependently blocked NPY-induced LH suppression and also inhibited NPY-stimulated food intake.\",\n      \"method\": \"Intracerebroventricular administration of selective NPY receptor agonists/antagonists in castrated rats, plasma LH RIA, competitive radioligand binding with Y5-specific assay\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic pharmacological receptor subtype dissection with multiple agonists/antagonists and biochemical endpoint\",\n      \"pmids\": [\"10465275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"NPY Y5 receptor activation mediates both the feeding response and reductions in energy expenditure: selective Y5 agonist D-[Trp32]-NPY (icv) stimulates food intake, reduces brown adipose tissue temperature, and decreases whole-body oxygen consumption, while Y1-, Y2-, and Y4-selective agonists do not reproduce these metabolic effects.\",\n      \"method\": \"ICV administration of receptor-selective NPY analogs in rats, food intake measurement, implanted BAT temperature transponders, indirect calorimetry\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological receptor subtype dissection with multiple physiological readouts, single study\",\n      \"pmids\": [\"10564216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human adipocytes express Y1 receptor (detected by RT-PCR and high-affinity radioligand binding with Y1-selective probes); Y1 receptor activation by NPY/PYY produces antilipolytic effects and enhances leptin secretion from adipocytes. These effects are blocked by selective Y1 antagonists (SR120819A, BIBP3226) and by pertussis toxin-insensitive GTPγS-binding, confirming Gi-coupled Y1 receptor signaling.\",\n      \"method\": \"RT-PCR, radioligand binding (125I-PYY, 125I-[Leu31,Pro34]PYY), [35S]GTPγS binding, lipolysis assay in isolated human adipocytes, leptin secretion ELISA, selective antagonist pharmacology\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods in human primary cells with functional readouts\",\n      \"pmids\": [\"10858507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"In goldfish, central (ICV) administration of the Y1-like receptor agonist [Leu31,Pro34]-NPY stimulates food intake to the same extent as NPY, while the Y2 agonist does not; this effect is blocked by the general NPY antagonist NPY(27-36). Furthermore, the opioid antagonist naloxone (ICV) blocks NPY-induced feeding, demonstrating that NPY's orexigenic effect in fish is mediated via Y1-like receptors and requires intact opioidergic signaling.\",\n      \"method\": \"ICV microinjection of selective NPY receptor agonists and antagonists in goldfish, food intake measurement, opioid antagonist (naloxone) pretreatment\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with epistasis between NPY and opioid systems, single study in teleost model\",\n      \"pmids\": [\"11068096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Y1 receptor knockout mice (Y1-/-) show dramatically reduced NPY-induced food intake after ICV NPY administration, establishing Y1 as the dominant receptor mediating NPY-induced feeding. Y5 receptor knockout mice show only partial reduction of feeding induced by Y5-preferring agonists but not NPY itself. Additionally, food intake induced by Y5-preferring agonists (PYY3-36, human/bovine PP) is reduced in Y1-/- mice, indicating indirect modulation through Y1 signaling.\",\n      \"method\": \"Y1-/- and Y5-/- knockout mouse generation, ICV administration of NPY and receptor-selective analogs, food intake measurement\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic KO models with defined pharmacological challenges\",\n      \"pmids\": [\"10698177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Ghrelin administered ICV strongly stimulates feeding in rats and activates Fos protein in NPY/AgRP neurons in the arcuate nucleus. Antibodies and antagonists against NPY and AgRP abolish ghrelin-induced feeding. Ghrelin augments NPY gene expression in the hypothalamus and blocks leptin-induced feeding suppression, placing NPY downstream of ghrelin and in competitive interaction with leptin in feeding regulation.\",\n      \"method\": \"ICV ghrelin injection, Fos immunohistochemistry, anti-NPY/AgRP antibody neutralization, NPY/AgRP antagonist pharmacology, RT-PCR for NPY mRNA, leptin interaction experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (IHC, neutralizing antibodies, antagonists, mRNA), replicated in ghrelin-deficient GH context\",\n      \"pmids\": [\"11196643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Fasting increases hypothalamic NPY and AGRP mRNA in parallel when leptin levels fall; leptin infusion (48 h via subcutaneous osmotic pump) in fasted lean rats almost completely reverses fasting-induced increases in both NPY and AGRP mRNA and restores POMC mRNA. In contrast, leptin-receptor-deficient Zucker (fa/fa) rats show upregulation of NPY but not AGRP mRNA, demonstrating that leptin acts via its receptor on arcuate neurons to suppress NPY expression.\",\n      \"method\": \"Solution hybridization/S1 nuclease protection assay for hypothalamic NPY, AGRP, POMC mRNA; subcutaneous leptin infusion; leptin receptor mutant rat models (Koletsky, Zucker fa/fa)\",\n      \"journal\": \"Journal of neuroendocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — leptin replacement experiment with specific mRNA readouts, replicated in two receptor-mutant rat models\",\n      \"pmids\": [\"11737554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Antidepressant-like activity of ICV NPY in the mouse forced swimming test is mediated via the Y1 receptor subtype: the Y1 agonist [Leu31,Pro34]PYY mimics NPY's anti-immobility effect; Y1 antagonists (BIBO3304, BIBP3226) block NPY's effect; Y2 agonist NPY(13-36) has no anti-immobility effect at tested doses; Y2 antagonist BIIE0246 is active but may reflect locomotor changes.\",\n      \"method\": \"ICV drug administration in mice, forced swimming test (immobility time), open field locomotor activity measurement, receptor-selective agonist/antagonist pharmacology\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic receptor subtype pharmacology with behavioral endpoint and locomotor controls\",\n      \"pmids\": [\"11927186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Ghrelin directly activates NPY neurons in the rat arcuate nucleus via Ca2+ signaling: single isolated ARC neurons respond to ghrelin (10-12–10-8 mol/L) with increased [Ca2+]i; ~80% of ghrelin-responsive neurons are NPY-immunopositive. The Ca2+ response is blocked by PKA inhibitors but not PKC inhibitors, and by N-type but not L-type Ca2+ channel blockers. Leptin attenuates ghrelin-induced Ca2+ increases in NPY neurons; orexin is additive with ghrelin.\",\n      \"method\": \"Enzymatic dissociation of rat ARC neurons, fura-2 single-cell Ca2+ imaging, immunocytochemical NPY identification, selective kinase inhibitors and channel blockers, glucose-sensing neuron identification\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct single-neuron Ca2+ imaging with pharmacological dissection of signaling cascade, NPY identity confirmed by immunocytochemistry\",\n      \"pmids\": [\"12663466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Chronic ICV infusion of the selective Y5 agonist D-Trp34NPY in C57BL/6J mice produces hyperphagia, obesity, increased adiposity, hyperinsulinemia, hyperleptinemia, and hypercholesterolemia; all effects are fully blocked by oral administration of a selective Y5 antagonist. Under pair-feeding, Y5 activation still reduces hormone-sensitive lipase activity in white adipose tissue and decreases UCP-1 mRNA in brown adipose tissue, indicating that Y5-mediated obesity involves both hyperphagia and metabolic changes (decreased lipolysis and thermogenesis).\",\n      \"method\": \"ICV infusion via osmotic minipump, pair-feeding paradigm, selective Y5 antagonist oral dosing, adipose tissue enzyme activity assay, UCP-1 RT-PCR\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective agonist plus antagonist rescue, pair-feeding controls dissect metabolic from caloric mechanisms\",\n      \"pmids\": [\"12697685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"NPY suppresses experimental autoimmune encephalomyelitis (EAE) via Y1 receptors: exogenous NPY and Y1 receptor agonists significantly inhibit EAE induction, while Y5 agonist or combined NPY + Y1 antagonist treatment does not. Y1 antagonist alone produces earlier EAE onset, demonstrating a protective role of endogenous NPY. The Y1 agonist inhibits myelin oligodendrocyte glycoprotein-specific Th1 responses and biases autoimmune T cells toward Th2, directly affecting T cells through Y1 receptors.\",\n      \"method\": \"Active EAE induction in C57BL/6 mice, selective NPY receptor agonist/antagonist treatment, clinical disease scoring, ex vivo T cell cytokine profiling, antigen-specific proliferation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — receptor-specific pharmacology with loss-of-function (antagonist) and gain-of-function (agonist), ex vivo mechanistic validation\",\n      \"pmids\": [\"14500640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NPY molecular recognition by Y receptors involves distinct binding poses: one conserved aspartate residue in the third extracellular loop is essential for ligand binding across all four Y receptors (Y1, Y2, Y4, Y5) but interacts with different arginine residues in the ligand depending on receptor subtype. The N terminus of NPY forms extensive interactions with Y1 but not with Y2 or Y4 receptors. These subtype-specific contacts were mapped by combining chemically modified peptide analogs, receptor mutagenesis, and chimeric receptors.\",\n      \"method\": \"Receptor mutagenesis (site-directed), chimeric receptor construction, peptide analog synthesis with chemical modifications, radioligand binding in transfected cells\",\n      \"journal\": \"Nutrition\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis plus chimeric receptors with multiple ligand variants, multiple receptor subtypes\",\n      \"pmids\": [\"18725086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ghrelin activates NPY/AgRP neurons through a UCP2-dependent mitochondrial mechanism. Ghrelin induces hypothalamic mitochondrial proliferation and electrical activation of NPY/AgRP neurons; these effects require UCP2. The UCP2-dependent mechanism is driven by a fatty acid oxidation pathway involving AMPK and CPT1, which generates free radicals that are scavenged by UCP2, thereby altering mitochondrial respiration and NPY/AgRP neuronal excitability. Ghrelin-triggered synaptic plasticity of POMC neurons and ghrelin-induced food intake are also UCP2-dependent.\",\n      \"method\": \"UCP2 knockout mice, hypothalamic mitochondrial respiration assays, AMPK and CPT1 pharmacological inhibitors, electrophysiology of NPY/AgRP neurons, reactive oxygen species measurement, electron microscopy of mitochondria, synaptic plasticity assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic KO plus pharmacological inhibition of pathway components, multiple orthogonal readouts (electrophysiology, ROS, mitochondrial morphology, behavior)\",\n      \"pmids\": [\"18668043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A SNP (rs16147) in the NPY promoter region alters NPY expression in vitro and accounts for more than half of the in vivo variation in NPY mRNA levels driven by haplotype. Lower haplotype-driven NPY expression predicts higher amygdala activation to emotional stimuli and diminished stress resilience (reduced endogenous opioid neurotransmission during pain/stress). NPY haplotypes predict plasma NPY levels and lymphoblast NPY mRNA levels.\",\n      \"method\": \"Haplotype analysis, in vitro promoter-reporter assay (SNP rs16147), post-mortem brain NPY mRNA quantification, lymphoblast mRNA, plasma NPY RIA, fMRI amygdala activation, PET endogenous opioid neurotransmission\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro functional promoter assay plus convergent multi-level human phenotypic validation\",\n      \"pmids\": [\"18385673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NPY promotes chemokinesis of dorsal root ganglion growth cones via an attractive turning response and increased growth rate mediated by the Y1 receptor, as demonstrated by asymmetric gradient application of NPY to cultured embryonic DRG neurons. Y1 receptor-deficient mice have fewer proliferating precursor cells and neuroblasts in the subventricular zone and rostral migratory stream and fewer neurons in the olfactory bulb, linking NPY-Y1 signaling to adult neurogenesis.\",\n      \"method\": \"Asymmetric NPY gradient application to embryonic DRG growth cone cultures (turning assay), Y1 and Y2 receptor knockout mouse analysis, SVZ/RMS BrdU proliferation assay, olfactory bulb neuron counting\",\n      \"journal\": \"Nutrition\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct growth cone turning assay plus genetic KO model with quantitative neurogenesis readout\",\n      \"pmids\": [\"18725084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Exogenous NPY Y2 receptor activation (NPY13-36, 300 nM) provides neuroprotection against AMPA-induced excitotoxicity in CA1 and CA3 pyramidal cells of mouse organotypic hippocampal slices, blocked by Y2 antagonist BIIE0246. Endogenous NPY provides additional neuroprotection revealed by Y1 antagonist (BIBP3226) or NPY-neutralizing antibody treatment. AMPA-induced neurodegeneration is associated with microglial BDNF release and upregulation of neuronal TrkB; this BDNF is not required for NPY Y2-mediated neuroprotection.\",\n      \"method\": \"Organotypic hippocampal slice culture, AMPA excitotoxicity model, propidium iodide uptake assay, selective Y1/Y2 receptor pharmacology, ELISA for BDNF, immunohistochemistry for TrkB and microglia\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological receptor dissection with quantitative cell death readout, mechanistic follow-up on BDNF pathway, single study\",\n      \"pmids\": [\"18412629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NPY promotes SVZ cell proliferation (neuroproliferation) and chemokinesis in rats via Y1 receptor-mediated activation of the ERK1/2 MAP kinase pathway, as established by pharmacological approaches. NPY is endogenously synthesized by SVZ cells, suggesting autocrine/paracrine action. NPY does not affect self-renewal of SVZ stem cells.\",\n      \"method\": \"SVZ cell culture, BrdU proliferation assay, pharmacological Y1 receptor antagonism, ERK1/2 pathway inhibitors and Western blot, chemokinesis assay, endogenous NPY synthesis confirmed by RT-PCR/immunostaining\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with multiple functional readouts, single lab\",\n      \"pmids\": [\"21175616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NPY inhibits posttranslational processing of POMC to α-MSH by decreasing prohormone convertase-2 (PC2) expression in hypothalamic cells, mediated through Y1 receptors and the transcription factor Egr-1. Intra-PVN NPY also decreases PC2 in PVN samples, reducing pro-TRH processing. Additionally, NPY attenuates α-MSH-induced TRH production by (1) decreasing α-MSH-induced CREB phosphorylation, and (2) reducing α-MSH levels in the PVN.\",\n      \"method\": \"Hypothalamic cell culture and in vivo intra-PVN injection, PC2 protein/mRNA quantification, Egr-1 transcription factor analysis, CREB phosphorylation Western blot, α-MSH and TRH peptide measurements, Y1 receptor antagonist pharmacology\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro plus in vivo mechanistic dissection of NPY's regulation of POMC processing, single lab\",\n      \"pmids\": [\"23321476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NPY promotes intestinal epithelial cell proliferation and reduces apoptosis via PI3K-β-catenin signaling and downregulation of miR-375. In NPY knockout mice, inflammation-induced tumorigenesis (DSS model) produces fewer and smaller polyps with reduced proliferation (PCNA, Ki67) and increased apoptosis (TUNEL) compared to wild-type. In vitro, NPY increases PCNA, β-catenin, c-Myc, and cyclin D1, and reduces p21 in epithelial cell lines. miR-375 inhibitor does not further enhance NPY-treated cells, indicating miR-375 acts downstream of NPY.\",\n      \"method\": \"NPY-/- knockout mice, DSS colitis-associated tumorigenesis model, intestinal epithelial cell lines (T84), PCNA/Ki67 IHC, TUNEL apoptosis assay, PI3K pathway inhibitors, β-catenin Western blot, miR-375 qRT-PCR, miR-375 inhibitor epistasis\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model plus in vitro mechanistic pathway dissection, single lab\",\n      \"pmids\": [\"27856419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Systemic NPY dose-dependently inhibits dural-evoked trigeminovascular neuronal firing in rat trigeminocervical complex (TCC) through Y1 receptor activation: the Y1 agonist reproduces NPY's inhibitory effect, while Y2 and Y5 agonists and the Y1 antagonist have no significant effect, establishing NPY as an antinociceptive peptide in the trigeminovascular system acting via Y1 receptors.\",\n      \"method\": \"In vivo electrophysiology in anesthetized rats (TCC neuronal recording), dural nociceptive stimulation, systemic NPY and receptor-selective agonist/antagonist administration\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo neurophysiology with pharmacological receptor dissection, single study\",\n      \"pmids\": [\"27023421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Insulin signaling specifically in NPY neurons controls food intake and energy expenditure: genetic deletion of the insulin receptor in NPY neurons (in both flies and mice) leads to increased energy stores, obesity, dysregulation of the GH/IGF-1 axis, and altered insulin sensitivity. This establishes an ancient insulin/NPY neuronal network governing energy homeostasis across phyla.\",\n      \"method\": \"Conditional insulin receptor knockout specifically in NPY neurons (mouse and Drosophila), food intake and energy expenditure measurements, body composition analysis, GH/IGF-1 axis assessment, insulin sensitivity testing\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific conditional KO in two species with multiple metabolic phenotypes\",\n      \"pmids\": [\"28580287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ascending skeletal interoceptive signaling (via PGE2/EP4) downregulates hypothalamic NPY expression: EP4 activation induces SMILE (small heterodimer partner-interacting leucine zipper protein) in the hypothalamus, which binds pCREB as a transcriptional heterodimer on Npy promoters to inhibit NPY expression. Knockout of EP4 in sensory nerves increases NPY, causing bone catabolism and fat anabolism. Inhibition of NPY Y1R accelerates free fatty acid oxidation in osteoblasts and rescues bone loss.\",\n      \"method\": \"EP4 conditional KO in sensory neurons, hypothalamic SMILE expression, ChIP/co-IP showing SMILE-pCREB interaction at Npy promoter, NPY promoter reporter assay, Y1R antagonist treatment, osteoblast fatty acid oxidation assay, bone phenotype analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus molecular promoter mechanism (SMILE-pCREB on Npy promoter), single study\",\n      \"pmids\": [\"34468315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of human Y1, Y2, and Y4 receptors in complex with NPY or pancreatic polypeptide and Gi1 protein reveal that the N-terminus of NPY forms extensive interactions specifically with Y1 but not with Y2 or Y4. Different receptors impose distinct binding poses on the peptide, reflecting conformational plasticity of NPY. Mutagenesis and functional studies confirmed subtype-specific receptor-peptide contacts, providing a structural basis for selective drug development.\",\n      \"method\": \"Cryo-EM structure determination, site-directed mutagenesis, functional signaling assays (cAMP, calcium), ligand binding assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures of three receptor subtypes plus mutagenesis and functional validation\",\n      \"pmids\": [\"35507650\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NPY is a 36-amino acid peptide derived from proteolytic processing of a 97-aa preproNPY precursor; it is co-stored with noradrenaline in large dense-cored vesicles of sympathetic neurons and released preferentially at high firing frequencies. NPY signals through four Gi-coupled GPCRs (Y1, Y2, Y4, Y5) whose structures show subtype-specific peptide binding poses; Y1 and Y2 couple to inhibition of cAMP and elevation of intracellular Ca2+ in a cell-type-specific manner depending on available G proteins. In the hypothalamus, NPY/AgRP neurons receive excitatory ghrelin input (via PKA/N-type Ca2+ channel signaling and a UCP2-dependent mitochondrial fatty acid oxidation pathway) and inhibitory leptin input (via leptin receptors on NPY neurons that suppress NPY mRNA), with NPY promoting food intake primarily through Y1 receptors (dominant role established by KO mice) and modulating energy expenditure through Y5 receptors. NPY also suppresses POMC-to-α-MSH processing by reducing PC2 via Egr-1/Y1 receptor signaling, inhibits LH secretion via Y5 receptors, mediates antidepressant-like and anxiolytic effects via amygdala Y1 receptors, promotes adult neurogenesis and growth cone attraction via Y1/ERK1/2 signaling, provides neuroprotection against excitotoxicity via Y2 receptors, and exerts antinociceptive effects in the trigeminovascular system through Y1 receptors; brain NPY levels are inversely related to ethanol consumption as demonstrated by reciprocal NPY knockout and overexpression models.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NPY is a 36-amino acid neuropeptide that functions as a central regulator of energy homeostasis, sympathetic neurotransmission, and neuromodulation by signaling through Gi-coupled Y1–Y5 receptors. Co-stored with noradrenaline in large dense-cored vesicles of sympathetic neurons and preferentially released during high-frequency stimulation, NPY acts as an independent sympathetic vasoconstrictor co-transmitter and potentiates noradrenaline-evoked vasoconstriction, while also driving smooth muscle proliferation via Y1-mediated p38/PKD signaling [PMID:2866663, PMID:2170253, PMID:24779394]. In the hypothalamus, NPY/AgRP neurons are activated by ghrelin through a UCP2-dependent mitochondrial fatty acid oxidation pathway and inhibited by insulin signaling, and NPY stimulates food intake and suppresses energy expenditure primarily through Y1 and Y5 receptors while reducing POMC-to-α-MSH processing via Y1-mediated downregulation of PC2/Egr-1 [PMID:18668043, PMID:28580287, PMID:23321476, PMID:10564216]. Beyond metabolic control, NPY promotes subventricular zone neurogenesis and axon guidance through Y1-ERK1/2 signaling, confers Y2-dependent neuroprotection against excitotoxicity, inhibits trigeminovascular nociceptive transmission via Y1 receptors, suppresses autoreactive Th1 responses through Y1, and exerts antilipolytic and leptin-secretory effects in adipocytes [PMID:21175616, PMID:18725084, PMID:18412629, PMID:27023421, PMID:14500640, PMID:10858507].\",\n  \"teleology\": [\n    {\n      \"year\": 1985,\n      \"claim\": \"Establishing NPY as a sympathetic co-transmitter: the question of whether NPY acts independently of noradrenaline during sympathetic vasomotor control was resolved by showing NPY co-localizes with NA in perivascular nerves and produces vasoconstriction resistant to adrenoceptor blockade, and that its synthesis and axonal transport are regulated by nerve activity.\",\n      \"evidence\": \"Immunohistochemistry, nerve ligation transport assays, blood flow measurement with pharmacological adrenoceptor blockade in peripheral tissues\",\n      \"pmids\": [\"2866663\", \"2858824\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of differential vesicle release at varying stimulation frequencies not defined\", \"No receptor subtype identification at this stage\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"Determining the solution structure of NPY: the question of whether NPY adopts a defined conformation relevant to receptor binding was answered by demonstrating a stable α-helical fold in aqueous solution with ~5 nM receptor affinity.\",\n      \"evidence\": \"Circular dichroism, sedimentation equilibria, radioligand binding of synthetic porcine NPY\",\n      \"pmids\": [\"2823169\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No atomic-resolution structure or receptor-bound conformation determined\", \"Oligomeric state ambiguous at this point\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Defining the rules of NPY co-release with noradrenaline: the question of what governs frequency-dependent NPY release and its modulation was resolved by demonstrating preferential release at high frequency, prejunctional α2/adenosine inhibition, angiotensin II facilitation, and autoinhibitory feedback.\",\n      \"evidence\": \"Overflow measurements and vascular contraction assays with pharmacological frequency-dependent stimulation of sympathetic nerves\",\n      \"pmids\": [\"2170253\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the vesicular release machinery for large dense-cored vesicles not specified\", \"Relative contribution of NPY versus NA at physiological firing rates in vivo unclear\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Receptor subtype assignment for central feeding and thermoregulation: the long-standing question of which receptor mediates hypothalamic NPY-induced feeding and hypothermia was answered by showing Y1 receptor antisense knockdown in the VMH abolished both responses.\",\n      \"evidence\": \"Bilateral VMH antisense oligodeoxynucleotide injection with body temperature telemetry and food intake measurement in rats\",\n      \"pmids\": [\"8760491\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antisense knockdown is transient and incomplete; genetic confirmation not yet available\", \"Relative Y1 vs Y5 contribution not fully resolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying Y5 as the receptor mediating NPY suppression of energy expenditure and reproductive axis: the questions of which receptor suppresses thermogenesis/BAT activity and inhibits LH secretion were answered by showing Y5-selective agonists uniquely reproduced these effects while Y1/Y2/Y4 agonists did not.\",\n      \"evidence\": \"ICV infusion of receptor-selective NPY analogs with BAT temperature, indirect calorimetry, and plasma LH radioimmunoassay in rats\",\n      \"pmids\": [\"10564216\", \"10465275\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No Y5 genetic knockout validation of these specific phenotypes\", \"Potential Y1/Y5 receptor heterodimerization not addressed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defining NPY's peripheral metabolic actions in adipocytes: the question of which receptor mediates NPY's antilipolytic and leptin-secretory effects was resolved by identifying Y1 receptor expression in human adipocytes and demonstrating full blockade of both responses by selective Y1 antagonists.\",\n      \"evidence\": \"RT-PCR, radioligand binding, lipolysis and leptin secretion assays with Y1-selective antagonists in isolated human adipocytes\",\n      \"pmids\": [\"10858507\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo adipose-specific contribution of NPY-Y1 signaling not tested\", \"Downstream intracellular pathway in adipocytes not mapped\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing NPY as an endogenous antidepressant-like peptide: the question of whether NPY modulates despair-related behavior and through which receptor was answered by showing Y1 agonists mimic and Y1 antagonists block NPY's anti-immobility effects in the forced swim test.\",\n      \"evidence\": \"ICV injection of receptor-selective agonists/antagonists in mouse forced swimming test with locomotion controls\",\n      \"pmids\": [\"11927186\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Forced swim test is a limited model of depression-related behavior\", \"Downstream neural circuitry not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating NPY's immunomodulatory role: the question of whether NPY influences autoimmune neuroinflammation was resolved by showing Y1 agonists suppress EAE and shift autoreactive T cells toward Th2, while Y1 antagonism accelerates disease.\",\n      \"evidence\": \"Active EAE model in mice with Y1/Y5 agonist and antagonist treatment, ex vivo T cell cytokine analysis\",\n      \"pmids\": [\"14500640\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct Y1 expression on T cells versus indirect CNS-mediated effects not dissected\", \"Mechanism of Th2 skewing not defined at the signaling level\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealing the mitochondrial mechanism linking ghrelin to NPY neuron activation: the question of how circulating ghrelin activates arcuate NPY/AgRP neurons was answered by demonstrating a UCP2-dependent pathway in which AMPK–CPT1-driven fatty acid oxidation generates ROS that UCP2 scavenges, enabling mitochondrial proliferation and electrical activation.\",\n      \"evidence\": \"UCP2 knockout mice, mitochondrial respiration assays, electrophysiology of NPY/AgRP neurons, AMPK/CPT1 pharmacological manipulation, food intake behavior\",\n      \"pmids\": [\"18668043\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this pathway operates identically in human hypothalamic neurons unknown\", \"Identity of the ROS sensor linking UCP2 to electrical activation not determined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linking NPY genetic variation to human stress resilience: the question of whether NPY expression variation has functional neural consequences was answered by identifying a promoter SNP (rs16147) that accounts for >50% of haplotype-driven NPY expression variation and predicts amygdala reactivity to emotional stimuli.\",\n      \"evidence\": \"Promoter-reporter assays, post-mortem brain mRNA, plasma NPY, fMRI, PET opioid neurotransmission imaging\",\n      \"pmids\": [\"18385673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal role of rs16147 in stress-related psychiatric disorders not confirmed by interventional study\", \"Epigenetic regulation of NPY promoter not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing NPY as a neurogenic and axon guidance factor: the questions of whether NPY promotes neurogenesis and directs axon growth were answered by showing Y1-mediated growth cone attraction in DRG neurons and reduced SVZ neurogenesis in Y1/Y2 KO mice.\",\n      \"evidence\": \"Growth cone turning assay, Y1/Y2 receptor KO mouse neurogenesis quantification, immunohistochemistry\",\n      \"pmids\": [\"18725084\", \"18412629\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Intracellular signaling cascade downstream of Y1 in growth cone turning not defined\", \"Whether NPY-dependent neurogenesis contributes to functional circuit integration not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Elucidating how NPY suppresses melanocortin signaling: the question of how NPY reduces α-MSH availability was answered by showing NPY acts through Y1 to downregulate PC2 via Egr-1, thereby inhibiting POMC processing and reducing α-MSH-driven CREB phosphorylation and TRH production in the PVN.\",\n      \"evidence\": \"Intra-PVN NPY in rats, PC2/Egr-1 quantification, Egr-1 knockdown, CREB phosphorylation, α-MSH and TRH measurement\",\n      \"pmids\": [\"23321476\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this mechanism operates in human hypothalamus not tested\", \"Long-term consequences for thyroid axis regulation not assessed in vivo\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defining NPY-Y1 vascular smooth muscle signaling in pulmonary hypertension: the question of which downstream pathways mediate Y1-driven vasoconstriction and proliferation was answered by identifying calcium mobilization, p38, and PKD as effectors, with Y1 upregulation in human pulmonary hypertension samples.\",\n      \"evidence\": \"Calcium imaging, wire myography, proliferation assays, Western blot for p38/PKD, Y1 antagonist BIBO 3304, patient tissue immunofluorescence\",\n      \"pmids\": [\"24779394\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role of NPY-Y1 in pulmonary hypertension pathogenesis not tested by genetic loss-of-function\", \"Whether Y1 upregulation is a cause or consequence of disease unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating insulin signaling within NPY neurons as a master regulator of energy balance: the question of how insulin acts directly on NPY neurons was answered by showing cell-type-specific insulin receptor deletion causes hyperphagia, obesity, and GH/IGF-1 dysregulation conserved from flies to mice.\",\n      \"evidence\": \"NPY neuron-specific insulin receptor knockout in mice and Drosophila, metabolic phenotyping, energy expenditure measurement\",\n      \"pmids\": [\"28580287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream transcriptional targets of insulin receptor signaling in NPY neurons not identified\", \"Whether insulin and leptin converge on common pathways within NPY neurons not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Uncovering NPY's role in skeleton–fat metabolic coupling: the question of how bone-derived interoceptive signals regulate adipose metabolism was answered by showing PGE2/EP4 signaling induces SMILE, which represses NPY transcription via pCREB, thereby promoting lipolysis and directing fatty acids to osteoblasts for bone formation.\",\n      \"evidence\": \"Conditional EP4 knockout in sensory neurons, SMILE knockin/knockout, ChIP on Npy promoter, fatty acid oxidation assays, bone histomorphometry\",\n      \"pmids\": [\"34468315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SMILE-pCREB interaction on the NPY promoter not confirmed by independent group\", \"Quantitative contribution of this axis versus other hypothalamic NPY regulators unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolving the structural basis of receptor subtype selectivity: the long-standing question of how NPY differentially engages Y1 versus Y2/Y4 receptors was answered by cryo-EM/crystal structures showing extensive N-terminal contacts with Y1 but not Y2/Y4, and identifying a conserved ECL3 aspartate essential for pan-Y receptor ligand binding.\",\n      \"evidence\": \"Cryo-EM and crystal structures of Y1/Y2/Y4 bound to NPY or PP with Gi1, mutagenesis, functional signaling assays\",\n      \"pmids\": [\"35507650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Y5 receptor structure not yet determined\", \"Dynamics of NPY–receptor interaction and G-protein coupling kinetics not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of Y5 receptor activation, the intracellular signaling networks that distinguish Y1- from Y5-mediated transcriptional programs in hypothalamic neurons, how NPY neuron activity is integrated with leptin and insulin signaling at the molecular level, and whether NPY-dependent neurogenesis contributes to functional circuit repair in the adult brain.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Y5 receptor structure unavailable\", \"Convergent signaling logic of insulin/leptin/ghrelin on NPY transcription not unified\", \"In vivo functional relevance of NPY-driven adult neurogenesis for behavior not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 3, 5, 8, 10, 11, 12, 14, 16, 22]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [7, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [11, 12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [11, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3, 5, 8, 10, 14, 16]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 9, 10, 22]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 22]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NPY1R\",\n      \"NPY2R\",\n      \"NPY5R\",\n      \"GNAI1\",\n      \"UCP2\",\n      \"AGRP\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"NPY is a 36-amino acid neuropeptide processed from a 97-amino acid precursor (preproNPY) that functions as a co-transmitter with noradrenaline in sympathetic neurons and as a major hypothalamic regulator of energy homeostasis, neuroendocrine function, and stress-related behavior [PMID:6589611, PMID:2858824, PMID:2170253]. NPY signals through Gi-coupled Y1, Y2, Y4, and Y5 receptors with subtype-specific binding poses — cryo-EM structures reveal that the NPY N-terminus engages Y1 but not Y2/Y4 — and couples to inhibition of cAMP and elevation of intracellular Ca²⁺ in a cell-type-dependent manner [PMID:1321422, PMID:7592910, PMID:35507650]. In the hypothalamus, NPY neurons integrate excitatory ghrelin input (via PKA/N-type Ca²⁺ channels and a UCP2-dependent mitochondrial fatty acid oxidation pathway) and inhibitory leptin input to drive feeding primarily through Y1 receptors — as established by Y1-knockout mice showing dramatically reduced NPY-induced food intake — while Y5 receptors mediate reductions in energy expenditure and suppression of LH secretion [PMID:18668043, PMID:11737554, PMID:10698177, PMID:10465275, PMID:12697685]. Beyond energy balance, NPY exerts Y1-mediated antidepressant-like and anxiolytic effects, promotes adult neurogenesis via Y1/ERK1/2 signaling, provides Y2 receptor-dependent neuroprotection against excitotoxicity, suppresses POMC-to-α-MSH processing through Y1/Egr-1-mediated downregulation of PC2, and modulates ethanol consumption as demonstrated by reciprocal knockout and overexpression models [PMID:11927186, PMID:21175616, PMID:18412629, PMID:23321476, PMID:9845072].\",\n  \"teleology\": [\n    {\n      \"year\": 1984,\n      \"claim\": \"Determining the full-length precursor structure of NPY was essential to understanding how the mature 36-amino acid peptide is generated; cDNA cloning from human pheochromocytoma revealed a 97-aa preproNPY processed at two sites into signal peptide, mature NPY, and a C-terminal peptide.\",\n      \"evidence\": \"cDNA cloning, nucleotide sequencing, in vitro translation with immunoprecipitation from human pheochromocytoma\",\n      \"pmids\": [\"6589611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Processing enzymes responsible for cleavage were not identified\", \"Functional role of the C-terminal peptide of NPY (CPON) remained unclear\"]\n    },\n    {\n      \"year\": 1985,\n      \"claim\": \"How NPY is stored and released in sympathetic nerves was unknown; multiple studies established that NPY is co-stored with noradrenaline in large dense-cored vesicles, transported anterogradely, and acts as a co-transmitter producing vasoconstriction through a non-adrenergic receptor mechanism.\",\n      \"evidence\": \"Immunohistochemistry, RIA, pharmacological lesions (6-OHDA, reserpine), axonal ligation transport assay, local blood flow measurement with α-adrenoceptor blockade\",\n      \"pmids\": [\"2858824\", \"2866663\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular identity of the NPY receptor mediating vasoconstriction was unknown\", \"Whether NPY release requires high-frequency versus tonic firing was not yet quantified\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Understanding how NPY gene expression is controlled required knowledge of its genomic structure; the human NPY gene was mapped to four exons spanning ~8 kb, and ~530 bp of 5′ flanking sequence was shown to be sufficient for promoter activity in neuronal cells.\",\n      \"evidence\": \"Genomic library cloning, primer extension, reporter gene transfection assay in CA-77 and PC12 cells\",\n      \"pmids\": [\"2427515\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factor binding sites within the promoter were not functionally dissected\", \"Tissue-specific regulatory elements beyond the proximal promoter were not identified\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"The rules governing frequency-dependent NPY release and its structure-activity relationships were established: NPY is preferentially released at high stimulation frequencies, auto-inhibits its own release, and requires an intact amidated C-terminus for receptor binding and cAMP inhibition.\",\n      \"evidence\": \"In vitro organ bath pharmacology, sympathetic nerve stimulation with overflow measurement, receptor binding, cAMP assays across multiple vascular beds\",\n      \"pmids\": [\"2170253\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor subtypes mediating prejunctional feedback inhibition were not identified\", \"Post-release metabolism/inactivation mechanisms for NPY were not addressed\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The molecular identities and signaling properties of the principal NPY receptors were resolved: cloning of Y1 (Gi-coupled, cAMP inhibition, cell-type-dependent Ca²⁺ coupling), Y2 (preferring C-terminal NPY fragments), and Y4 (preferring pancreatic polypeptide) established the receptor family's pharmacological and signaling diversity.\",\n      \"evidence\": \"Expression cloning, heterologous expression in HEK-293 and CHO cells, radioligand binding, cAMP and intracellular Ca²⁺ assays, pertussis toxin sensitivity\",\n      \"pmids\": [\"1321422\", \"7592910\", \"7559383\", \"7493937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Y5 receptor had not yet been cloned\", \"Structural basis for subtype-selective ligand recognition was unknown\", \"Downstream effectors beyond cAMP/Ca²⁺ were not characterized\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Whether endogenous NPY levels influence ethanol-related behavior was untested; reciprocal genetic models showed that NPY-knockout mice consume more ethanol with reduced sedative sensitivity, while NPY-overexpressing mice show the opposite, establishing an inverse NPY–ethanol relationship.\",\n      \"evidence\": \"NPY-/- knockout and neuronal NPY-overexpressing transgenic mice, two-bottle ethanol preference, ethanol-induced sleep test\",\n      \"pmids\": [\"9845072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which NPY receptor subtype mediates ethanol-related effects was not determined\", \"Brain regional specificity of NPY's anti-ethanol effect was unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The receptor subtype hierarchy for NPY-induced feeding was disputed; Y1-knockout mice showed dramatically reduced NPY-induced feeding while Y5-knockout mice showed only partial attenuation, establishing Y1 as the dominant orexigenic receptor and Y5 as a modulator of energy expenditure and LH secretion.\",\n      \"evidence\": \"Y1-/- and Y5-/- knockout mice with ICV NPY/selective agonist administration, food intake measurement; separate studies with Y5 agonists measuring BAT temperature and oxygen consumption; Y5 pharmacology for LH suppression\",\n      \"pmids\": [\"10698177\", \"10564216\", \"10465275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Y1 and Y5 cooperate on the same neurons or distinct circuits was unclear\", \"Compensatory receptor upregulation in KO models was not assessed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The hierarchical relationship between ghrelin, leptin, and NPY in hypothalamic feeding circuits was unknown; ghrelin was shown to activate Fos in NPY/AgRP neurons and require intact NPY/AgRP signaling for its orexigenic effect, while leptin suppresses fasting-induced NPY mRNA via its receptor on arcuate neurons.\",\n      \"evidence\": \"ICV ghrelin with Fos IHC, anti-NPY/AgRP antibody neutralization, NPY mRNA RT-PCR; leptin infusion in fasted rats and leptin-receptor-mutant models with NPY mRNA quantification\",\n      \"pmids\": [\"11196643\", \"11737554\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct electrophysiological confirmation of ghrelin-to-NPY neuron activation was pending\", \"Intracellular signaling cascade from ghrelin receptor to NPY transcription was unresolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"How ghrelin signal transduction reaches NPY neurons at the single-cell level was resolved: ghrelin directly elevates [Ca²⁺]i in NPY-immunopositive arcuate neurons via PKA and N-type Ca²⁺ channels, with leptin acting as a direct antagonist of this response.\",\n      \"evidence\": \"Enzymatic dissociation of rat arcuate neurons, fura-2 Ca²⁺ imaging, NPY immunocytochemistry, PKA/PKC inhibitors, N-type/L-type channel blockers\",\n      \"pmids\": [\"12663466\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ghrelin modulates NPY vesicular release in addition to excitability was untested\", \"Downstream transcriptional consequences of the PKA/Ca²⁺ cascade in NPY neurons were not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Multiple mechanistic advances converged: (1) ghrelin activation of NPY/AgRP neurons requires UCP2-dependent mitochondrial fatty acid oxidation via AMPK/CPT1; (2) an NPY promoter SNP (rs16147) accounts for >50% of in vivo NPY expression variation and predicts amygdala stress reactivity; (3) NPY-Y1 signaling drives adult neurogenesis via ERK1/2 and neuroprotection occurs via Y2 receptors; (4) subtype-specific receptor–peptide contacts were mapped showing the NPY N-terminus engages Y1 but not Y2/Y4.\",\n      \"evidence\": \"UCP2-KO mice with electrophysiology and mitochondrial assays; haplotype-promoter-reporter assays with fMRI and PET imaging; Y1-KO SVZ neurogenesis quantification and growth cone turning assays; receptor mutagenesis/chimera binding studies\",\n      \"pmids\": [\"18668043\", \"18385673\", \"18725084\", \"18412629\", \"18725086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The full mitochondrial signaling pathway from UCP2 to membrane depolarization in NPY neurons was incompletely characterized\", \"Whether the rs16147 promoter variant affects NPY levels in specific brain nuclei was unresolved\", \"Structural resolution of receptor–peptide complexes at atomic level was still lacking\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"How NPY antagonizes the melanocortin system at a post-translational level was unknown; NPY was shown to suppress prohormone convertase-2 (PC2) expression via Y1/Egr-1 signaling, thereby reducing POMC-to-α-MSH processing and α-MSH-induced CREB phosphorylation in hypothalamic neurons.\",\n      \"evidence\": \"Hypothalamic cell culture and in vivo intra-PVN NPY injection, PC2 mRNA/protein quantification, Egr-1 analysis, CREB phosphorylation Western blot, Y1 antagonist pharmacology\",\n      \"pmids\": [\"23321476\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this mechanism operates in the arcuate nucleus or only in PVN was unclear\", \"The contribution of PC2 suppression versus direct synaptic inhibition to NPY's net anti-melanocortin effect was not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether insulin acts directly on NPY neurons to regulate energy balance was untested; conditional deletion of the insulin receptor specifically in NPY neurons in both mice and Drosophila produced obesity and altered GH/IGF-1 signaling, establishing an evolutionarily conserved insulin–NPY neuronal axis.\",\n      \"evidence\": \"Conditional insulin receptor knockout in NPY neurons (mouse and Drosophila), metabolic phenotyping including body composition, food intake, energy expenditure, GH/IGF-1 axis assessment\",\n      \"pmids\": [\"28580287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether insulin directly regulates NPY transcription or only neuronal excitability was not distinguished\", \"Interaction between insulin and leptin/ghrelin signaling within NPY neurons was not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A peripheral-to-central regulatory loop for NPY was discovered: skeletal PGE2/EP4 signaling induces the co-repressor SMILE in the hypothalamus, which binds pCREB on the Npy promoter to suppress NPY transcription, linking bone-derived interoception to hypothalamic NPY control of bone and fat metabolism.\",\n      \"evidence\": \"EP4 conditional KO in sensory neurons, ChIP and co-IP for SMILE–pCREB on Npy promoter, NPY promoter reporter, Y1R antagonist rescue of bone phenotype, osteoblast fatty acid oxidation assay\",\n      \"pmids\": [\"34468315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SMILE–pCREB interaction on the Npy promoter operates in all hypothalamic nuclei or is regionally restricted is unknown\", \"Independent replication of the skeletal interoceptive pathway is lacking\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Atomic-resolution understanding of NPY–receptor recognition was achieved: cryo-EM structures of Y1, Y2, and Y4 in complex with NPY/PP and Gi1 confirmed that the NPY N-terminus makes extensive contacts with Y1 but not Y2/Y4, providing the structural basis for subtype-selective pharmacology.\",\n      \"evidence\": \"Cryo-EM structure determination of three receptor–ligand–Gi complexes, site-directed mutagenesis, cAMP and Ca²⁺ functional assays\",\n      \"pmids\": [\"35507650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Y5 receptor structure in complex with NPY has not been determined\", \"Conformational dynamics of NPY upon receptor binding are not captured by static cryo-EM\", \"Structure-guided selective agonist/antagonist design has not yet been validated in vivo\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of Y5 receptor selectivity, the circuit-level integration of insulin/leptin/ghrelin inputs onto individual NPY neurons, the precise mechanism by which UCP2-dependent mitochondrial changes translate to NPY neuronal firing, and whether NPY's peripheral metabolic effects on adipocytes and bone are therapeutically targetable.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No Y5 receptor structure available\", \"Single-cell resolution of convergent hormonal inputs on NPY neurons is lacking\", \"In vivo therapeutic validation of NPY-receptor-selective compounds for metabolic or psychiatric indications is absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [5, 6, 7, 15, 24, 35]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13, 14, 30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 5, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7, 8, 15, 24, 35]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [12, 20, 21, 25, 26, 28]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 30]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [23]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NPY1R\",\n      \"NPY2R\",\n      \"NPY5R\",\n      \"NPY4R\",\n      \"GHSR\",\n      \"LEPR\",\n      \"UCP2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}