{"gene":"TACR1","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":1991,"finding":"The human substance P receptor (NK-1/TACR1) was cloned as a 407-amino-acid G-protein-coupled receptor; when expressed in COS-7 cells it binds substance P with Kd ~0.24–0.35 nM and its stimulation triggers rapid, transient inositol 1,4,5-trisphosphate production, establishing Gq/phospholipase C as its primary intracellular effector. The gene resides on human chromosome 2 as a single-copy locus.","method":"cDNA cloning, heterologous expression in COS-7 cells, radioligand binding, IP3 assay, chromosome mapping with mouse/human hybrids","journal":"Biochemistry / Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — independent cloning in two labs with functional reconstitution (IP3, radioligand binding) in the same year","pmids":["1657150","1718267"],"is_preprint":false},{"year":1992,"finding":"The human TACR1 gene contains five exons with intron positions conserved with the NK-2 (neuromedin K) receptor gene, consistent with evolution from a common ancestral GPCR gene. The gene spans ~60 kb.","method":"Genomic DNA cloning and sequencing, Southern blot, restriction mapping","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — direct genomic sequencing of the human locus","pmids":["1312928"],"is_preprint":false},{"year":1992,"finding":"Two isoforms of the human NK-1 receptor (long and short/truncated) arise from alternative pre-mRNA splicing. The long form binds substance P with high affinity and activates oscillating Cl⁻ currents in Xenopus oocytes. The short form binds substance P with ≥10-fold lower affinity and elicits only weak electrophysiological responses, indicating the C-terminal cytoplasmic tail is required for full agonist coupling and signaling efficacy.","method":"cDNA cloning, heterologous expression in COS cells and Xenopus oocytes, radioligand binding, electrophysiology","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in two heterologous systems with pharmacological and electrophysiological readouts","pmids":["1310144"],"is_preprint":false},{"year":1992,"finding":"The N-terminal extracellular domain of NK-1R is required for high-affinity peptide binding: mutagenesis of residues in the N-terminus reduced affinity for substance P, substance K, and a C-terminal SP analog, but not for a non-peptide antagonist. Val-97 in the second extracellular segment selectively influences neurokinin B affinity, implicating distinct extracellular determinants for peptide selectivity.","method":"Site-directed mutagenesis, heterologous expression in COS cells, radioligand competition binding","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with functional binding readout","pmids":["1280161"],"is_preprint":false},{"year":1992,"finding":"Systematic extracellular domain substitutions revealed that three residues in the first extracellular segment and two in the second are required for optimal binding of all three natural tachykinin peptide agonists; the third and fourth extracellular segments partially determine NK-1R subtype selectivity of the non-peptide antagonist L-703,606, showing that agonist and antagonist binding domains are spatially distinct.","method":"Chimeric receptor construction, mutagenesis, heterologous expression, radioligand competition binding","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with systematic chimeric/mutagenesis mapping","pmids":["1281469"],"is_preprint":false},{"year":1993,"finding":"Histidine 197 in the fifth transmembrane helix of the human NK-1R forms an amino-aromatic interaction specifically with the benzhydryl moiety of the non-peptide antagonist CP 96345 but not with peptide agonists, defining a transmembrane antagonist-binding pocket distinct from the extracellular peptide-binding site.","method":"Site-directed mutagenesis, heterologous expression, radioligand binding, structure-activity analysis of antagonist analogues","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with orthogonal SAR validation; published in Nature","pmids":["8384323"],"is_preprint":false},{"year":1996,"finding":"An antibody targeting the third extracellular region (ECR-3) of rat brain NK1R blocked >95% of [¹²⁵I]-SP binding to intact C6 astrocytes and CHO cells expressing NK1R, confirming the third extracellular loop is surface-exposed and participates in ligand access. Immunoaffinity purification from rat brain yielded bands of ~54 kDa and ~44 kDa on SDS-PAGE.","method":"Peptide-immunized antibody generation, radioligand binding inhibition, Western blot, affinity purification from rat brain membranes","journal":"Journal of neuroimmunology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal functional antibody blocking plus biochemical characterization; single lab","pmids":["8707930"],"is_preprint":false},{"year":1998,"finding":"Genetic ablation of the NK-1 receptor (TACR1) in mice abolished wind-up amplification of nociceptive reflexes and intensity coding in the dorsal horn, demonstrating that NK-1R–mediated substance P signaling is required for the full development of central sensitization. NK-1R was also essential for stress-induced analgesia and aggression, but not for acute pain or hyperalgesia.","method":"Targeted gene knockout in mice, behavioral nociception assays (wind-up, tail-flick, hot-plate), electrophysiology of spinal dorsal horn neurons","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined electrophysiological and behavioral phenotypes; published in Nature","pmids":["9537323"],"is_preprint":false},{"year":1998,"finding":"Blockade of central NK-1 receptors by the non-peptide antagonist MK-869 produced antidepressant effects in a placebo-controlled clinical trial, and in preclinical studies NK-1R antagonists suppressed isolation-induced vocalizations without interacting with monoamine systems in the manner of established antidepressants, establishing a monoamine-independent mechanism for NK-1R in mood regulation.","method":"Randomized placebo-controlled clinical trial; preclinical vocalization suppression assay; receptor binding and monoamine interaction studies","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — clinical trial plus orthogonal preclinical mechanism studies; published in Science","pmids":["9733503"],"is_preprint":false},{"year":2001,"finding":"NK1R-/- mice phenocopied the behavioral effects of NK1R antagonists in antidepressant-relevant assays (forced swim, resident-intruder), and both genetic and pharmacological inactivation of NK1R did not produce sedation or motor impairment, validating that the antidepressant-like phenotype requires absence of functional NK1R signaling rather than developmental compensation.","method":"NK1R knockout mice vs. NK1R antagonists (L-760735, GR205171) in behavioral assays; central receptor occupancy confirmed by agonist-challenge test","journal":"Behavioural pharmacology","confidence":"High","confidence_rationale":"Tier 2 — orthogonal genetic and pharmacological approaches in multiple species and assays","pmids":["11742144"],"is_preprint":false},{"year":2003,"finding":"The long NK-1R isoform is the dominant form in human brain (quantified by TaqMan PCR), with highest levels in locus coeruleus and ventral striatum, whereas the truncated isoform predominates in peripheral tissues; ³H-SP autoradiography correlated with mRNA distribution, linking isoform-specific expression to region-specific functions in mood and stress circuits.","method":"Riboprobe in situ hybridization, quantitative TaqMan PCR, in vitro autoradiography with ³H-SP","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in human brain; strong anatomical-functional correlation","pmids":["12752772"],"is_preprint":false},{"year":2003,"finding":"Substance P and the NK-1R in nucleus tractus solitarius and area postrema brainstem nuclei are critical mediators of the emetic reflex; NK-1R antagonists block emesis triggered by diverse stimuli (chemotherapy, motion, apomorphine) in animal models, placing NK-1R downstream of multiple emetic pathways converging on brainstem integrative nuclei.","method":"NK-1R antagonist pharmacology in ferret/cat emesis models; lesion and microinjection studies targeting brainstem nuclei","journal":"Journal of pharmacological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection across multiple emetic stimuli; single-lab review synthesis","pmids":["12686752"],"is_preprint":false},{"year":2003,"finding":"Endokinins A and B (EKA/B), encoded by the tachykinin precursor 4 gene, display equivalent affinity for the NK-1 receptor as substance P and produce identical hemodynamic effects in rats, identifying them as additional endogenous agonists for TACR1 at peripheral SP receptors.","method":"Radioligand competition binding at NK-1R, in vivo hemodynamic measurements in rats","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct radioligand binding plus in vivo functional equivalence demonstrated","pmids":["12716968"],"is_preprint":false},{"year":2004,"finding":"NK-1R localizes to lipid rafts and caveolae at the plasma membrane; cholesterol depletion with methyl-β-cyclodextrin abolishes NK1R-mediated signaling. Upon substance P stimulation, activated PKC translocates from cytoplasm specifically to lipid rafts, demonstrating that raft integrity is required for productive NK1R–PKC coupling.","method":"Sucrose gradient fractionation, immunofluorescence, cholesterol depletion/replenishment assay, PKC translocation assay in HEK293 and HepG2 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1/2 — biochemical fractionation plus functional cholesterol-depletion rescue experiment; multiple cell lines","pmids":["15590676"],"is_preprint":false},{"year":2004,"finding":"The C-terminal tail of NK-1R (truncated by 50 residues) retains interaction with both SNX1 (sorting nexin 1) and GASP (G protein-coupled receptor-associated sorting protein) as well as NSF, identifying an extended C-terminal binding epitope that directs post-endocytic trafficking of the receptor toward lysosomal degradation versus recycling pathways.","method":"GST pull-down library screen of 59 receptor C-terminal tails; SPR kinetics confirmation for selected hits; NK-1R truncation mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic GST pull-down across receptor library plus SPR kinetic validation and truncation mapping","pmids":["15452121"],"is_preprint":false},{"year":2004,"finding":"IL-1β upregulates NK-1R expression in human astroglioma cells and primary rat astrocytes at both mRNA and protein levels via NF-κB activation; the induced NK-1R is functional (SP triggers Ca²⁺ mobilization), and NF-κB inhibitor CAPE blocks both the promoter activation and the induction of NK-1R gene expression.","method":"Western blot, RT-PCR, Ca²⁺ imaging, NF-κB reporter assay, pharmacological inhibition in human astroglioma (U87 MG) and primary rat astrocytes","journal":"Glia","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (mRNA, protein, Ca²⁺ function, NF-κB reporter) in two cell models","pmids":["15390113"],"is_preprint":false},{"year":2007,"finding":"NK1R-/- mice display elevated basal extracellular noradrenaline in frontal cortex (2–4× higher than wildtype) associated with desensitization/reduced GTPγS coupling of somatodendritic α2a-adrenoceptors in locus coeruleus, demonstrating that tonic NK1R signaling normally suppresses noradrenergic tone through α2a-autoreceptor regulation.","method":"In vivo microdialysis (anaesthetized and freely moving mice), [³⁵S]GTPγS autoradiography of locus coeruleus, Western blot for noradrenaline transporter, α2-antagonist pharmacology","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — in vivo microdialysis combined with receptor autoradiography and pharmacological validation; multiple readouts","pmids":["17331215"],"is_preprint":false},{"year":2008,"finding":"Human peripheral blood monocytes express exclusively the truncated NK-1R isoform (NK1R-T), which lacks the C-terminal 96-aa cytoplasmic domain. NK1R-T does not mobilize Ca²⁺ alone but enhances CCL5/CCR5-mediated Ca²⁺ mobilization and chemotaxis through ERK1/2 (selectively activating ERK2 alone), and induces serine phosphorylation of CCR5, revealing cross-receptor crosstalk at the receptor level.","method":"Flow cytometry, RT-PCR, Ca²⁺ imaging, chemotaxis assay, Western blot for ERK1/2 phosphorylation, CCR5 serine phosphorylation assay; NK1R-F transfection comparator","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods; isoform-specific effects confirmed by transfection rescue","pmids":["18835883"],"is_preprint":false},{"year":2008,"finding":"Chronic stress-induced upregulation of spinal NK1R expression depends on microglial p38 MAPK activation; minocycline (microglia inhibitor) blocked both NK1R upregulation and visceral hyperalgesia, while the p38 inhibitor SB203580 blocked hyperalgesia without blocking NK1R upregulation, placing microglial activation upstream of spinal NK1R increase and dissociating the two downstream effects.","method":"Water-avoidance stress rat model, Western blot and immunostaining for NK1R/OX42/P-p38, intrathecal drug delivery, colorectal distension visceromotor response","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — in vivo epistasis with two pharmacological tools dissecting pathway; functional and biochemical readouts","pmids":["19249394"],"is_preprint":false},{"year":2009,"finding":"NK1R-/- mice exhibit hyperactivity that is reversed by psychostimulants (d-amphetamine, methylphenidate), mirroring ADHD. In vivo microdialysis revealed >50% reduction in spontaneous dopamine efflux in prefrontal cortex and abolished striatal dopamine response to d-amphetamine in NK1R-/- mice, demonstrating that NK1R signaling tonically maintains dopaminergic tone in frontocortical and striatal circuits.","method":"Locomotor activity measurement, in vivo microdialysis (prefrontal cortex and striatum), NK1R antagonist (L-760735) pharmacology, psychostimulant challenge","journal":"Journal of psychopharmacology","confidence":"High","confidence_rationale":"Tier 2 — in vivo microdialysis with genetic and pharmacological convergent evidence; genotype–pharmacology interaction","pmids":["19204064"],"is_preprint":false},{"year":2009,"finding":"NK1R-/- mice survive hyperoxia (90% O₂) significantly worse than wildtype (median survival 84 h vs. 120 h), with increased lung inflammation, edema, and apoptosis (TUNEL), demonstrating a paradoxical protective role for NK1R in hyperoxic lung injury. In cultured lung epithelial cells, exogenous SP promoted cell death under hyperoxia, revealing distinct tissue-level versus cell-autonomous signaling by the SP/NK1R axis.","method":"NK1R-/- and TRPV1-/- mouse hyperoxia model, BAL fluid analysis, TUNEL staining, metallothionein/Na-K-ATPase Western blot, cell culture SP treatment under hyperoxia","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined phenotype plus in vitro mechanistic follow-up; single lab","pmids":["19633070"],"is_preprint":false},{"year":2009,"finding":"Prolonged exposure of NK1R to substance P decreases NK1R mRNA in bladder urothelium and upregulates specific miRNAs (miR-449b, miR-500, miR-328, miR-320) that directly correlate with NK1R mRNA/protein downregulation, identifying a miRNA-mediated negative feedback loop regulating NK1R expression.","method":"RT-PCR, Western blot, miRNA expression profiling, correlation analysis in cell models and human bladder biopsy specimens from BPS patients","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 3 — expression correlation plus cell-based SP stimulation data; miRNA-NK1R link shown by correlation and cell model only","pmids":["20008142"],"is_preprint":false},{"year":2010,"finding":"NK1R deletion or antagonism with L-703,606 reduces voluntary alcohol consumption and alcohol-conditioned place preference in a gene-dose-dependent manner; escalation of intake after repeated deprivation cycles occurs in wildtype but not NK1R-/- mice, identifying NK1R as a direct (non-developmental) regulator of alcohol reward and motivational escalation.","method":"Two-bottle free-choice intake, conditioned place preference, deprivation-escalation model in C57BL/6 NK1R-/- mice; NK1R antagonist receptor-specificity confirmed in KO","journal":"Psychopharmacology","confidence":"High","confidence_rationale":"Tier 2 — convergent genetic deletion and pharmacological receptor-specific blockade with multiple behavioral paradigms","pmids":["20112009"],"is_preprint":false},{"year":2011,"finding":"Substance P activates both contractile (MLC₂₀ phosphorylation) and pro-inflammatory (p38-MAPK, ERK1/2) pathways in lymphatic muscle cells via NK1R and NK3R. ERK1/2 inhibition reduces p-MLC₂₀ in a PKC-dependent manner, demonstrating crosstalk between the inflammatory and contractile cascades downstream of SP receptor activation in lymphatics.","method":"Rat mesenteric lymphatic muscle cell culture, pharmacological inhibitors, Western blot for p-MLC₂₀, p-p38, p-ERK1/2, NK1R/NK3R expression confirmed by RT-PCR","journal":"Microcirculation","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection with multiple kinase readouts; single-lab cell culture model","pmids":["21166923"],"is_preprint":false},{"year":2013,"finding":"Elevated Tacr1 expression in prefrontal cortex and central amygdala of alcohol-preferring (P) rats, driven in part by a -1372C allele that increases GATA-2/E2F-1 transcription factor binding and promoter activity, confers heightened sensitivity to NK1R antagonist (L822429) effects on alcohol self-administration; central amygdala infusion of L822429 replicates systemic effects, localizing NK1R's role in alcohol intake to this region.","method":"Operant self-administration, microinfusion, Tacr1 qPCR, NK1R autoradiography, Tacr1 promoter sequencing, EMSA, luciferase reporter assay","journal":"Biological psychiatry","confidence":"High","confidence_rationale":"Tier 1/2 — luciferase reporter + EMSA for promoter mechanism; microinfusion + behavioral readout for circuit localization; multiple orthogonal methods","pmids":["23419547"],"is_preprint":false},{"year":2014,"finding":"NK-1R full-length and truncated isoforms are differentially expressed across glioblastoma cell lines; only cell lines with high full-length NK1R (e.g., LN319) show significant SP conjugate binding, receptor internalization, and targeted cell killing by saporin-SP toxin, establishing that full-length NK1R isoform expression is required for SP-mediated receptor internalization and targeted cytotoxicity.","method":"RT-PCR for isoform quantification, radioligand binding (¹⁷⁷Lu-SP), fluorescence-labeled SP internalization, saporin-SP cytotoxicity assay in 4 GBM cell lines","journal":"Cancer biotherapy & radiopharmaceuticals","confidence":"Medium","confidence_rationale":"Tier 2 — multiple assays across cell lines linking isoform to functional internalization; single lab","pmids":["24552486"],"is_preprint":false},{"year":2017,"finding":"NK1R signals from endosomes (not only the plasma membrane) to produce sustained neuronal excitation and pain: after SP stimulation, NK1R undergoes clathrin/dynamin/β-arrestin–dependent endocytosis required for activation of cytosolic PKC and nuclear ERK as well as transcription. Endocytosis inhibitors block sustained spinal neuron excitation in vitro and nociception in vivo. Cholestanol-conjugated NK1R antagonists that target endosomal membranes provide more effective and prolonged antinociception than conventional antagonists.","method":"Pharmacological/genetic disruption of clathrin, dynamin, β-arrestin in spinal cord slice electrophysiology and in vivo pain models; cholestanol-conjugated antagonist synthesis and testing; PKC/ERK activation assays; mouse nociception models","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 1 — multiple genetic and pharmacological tools dissecting endosomal signaling; in vitro and in vivo functional validation; novel membrane-targeted drug strategy","pmids":["28566424"],"is_preprint":false},{"year":2018,"finding":"In pancreatic cancer, MMP1 secreted by cancer cells activates PAR1 on dorsal root ganglion neurons, which then release substance P; SP activates NK1R on pancreatic cancer cells to enhance migration, invasion, and perineural invasion via SP/NK1R/ERK signaling. Silencing MMP1 or blocking NK1R or PAR1 inhibited perineural invasion in vitro and in vivo.","method":"Matrigel/DRG co-culture PNI model, sciatic nerve invasion mouse model, shRNA knockdown, NK1R/PAR1 antagonists, Western blot for p-ERK, MRI with iron oxide nanoparticles","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 2 — in vitro and in vivo models with genetic and pharmacological convergence; defined SP/NK1R/ERK pathway","pmids":["29896303"],"is_preprint":false},{"year":2021,"finding":"A spinoparabrachial circuit defined by Tacr1 expression drives ongoing pain: Tacr1-expressing spinal projection neurons (NK1R+) target a small cluster of neurons in the superior lateral parabrachial nucleus (PBN-SL) that also express Tacr1; chemogenetic silencing of PBN-SLTacr1 neurons causes mice to ignore long-lasting noxious stimuli, while activation heightens nocifensive behavior and suppresses itch, establishing this circuit as essential for sustained (but not acute) pain processing.","method":"Chemogenetics (DREADD), optogenetics, optotagging to identify ON cells, Tacr1-Cre mouse intersectional genetics, behavioral nociception and itch assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic circuit-dissection tools (chemogenetics, optogenetics, optotagging) with defined behavioral phenotypes","pmids":["33591273"],"is_preprint":false},{"year":2021,"finding":"NK1R inhibition with aprepitant after intracerebral hemorrhage promotes M2 microglial polarization and hematoma clearance by downregulating the PKC/p38MAPK/NFκB signaling pathway; NK1R agonist or PKC agonist reversed these effects, placing NK1R upstream of PKC/p38MAPK/NFκB in post-hemorrhagic neuroinflammation. Thrombin injection increased substance P, identifying thrombin as an upstream activator of the NK1R axis after ICH.","method":"Mouse ICH model (autologous blood injection), Western blot, immunofluorescence, intracerebroventricular NK1R agonist/PKC agonist reversal experiments, neurobehavioral testing","journal":"Neurotherapeutics","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological epistasis with agonist reversal experiments defining pathway order; in vivo model","pmids":["34244927"],"is_preprint":false},{"year":2022,"finding":"After intracerebral hemorrhage, NK1R activation drives NLRC4-dependent neuronal pyroptosis via a PKCδ-dependent pathway; aprepitant (NK1R antagonist) reduced NLRC4, cleaved-caspase-1, GSDMD, IL-1β and IL-18, and these neuroprotective effects were abolished by NK1R agonist GR73632 or PKCδ agonist PMA, while NLRC4 siRNA recapitulated aprepitant's effects, placing NK1R→PKCδ→NLRC4 as a sequential pyroptosis pathway.","method":"Mouse ICH model, Western blot, immunofluorescence, intracerebroventricular siRNA knockdown, agonist reversal experiments, neurobehavioral assays","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 — genetic (siRNA) and pharmacological epistasis in vivo defining sequential pathway; single lab","pmids":["35922848"],"is_preprint":false},{"year":2022,"finding":"Tacr1-expressing ON cells in the rostral ventromedial medulla (RVM) exert inhibitory control over spinal pruriceptive transmission: intramedullary substance P potentiated RVM ON-cell firing and reduced pruritogen-evoked scratching while producing mild mechanical sensitization; chemogenetic activation of RVM Tacr1+ neurons reduced acute itch; optotagging confirmed Tacr1+ neurons are ON cells.","method":"Intramedullary microinjection of SP, chemogenetics (DREADD), optotagging electrophysiology in Tacr1-Cre mice, behavioral pruritogen scratching assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — chemogenetics plus optotagging plus pharmacology converge on same functional conclusion","pmids":["35972457"],"is_preprint":false},{"year":2023,"finding":"Activation of the SP/NK1R axis in breast cancer MCF-7 cells drives ROS accumulation and NF-κB-mediated upregulation of pro-inflammatory cytokines (TNF-α, IL-6) while downregulating p21; aprepitant (NK1R antagonist) reverses these effects and induces p53-mediated p21 upregulation, placing NK1R upstream of the ROS/NF-κB/p53 axis controlling cancer cell proliferation.","method":"ROS assay (H2DCFDA), qRT-PCR, resazurin viability assay, SP and aprepitant dose-response in MCF-7 cells","journal":"Cell biochemistry and biophysics","confidence":"Low","confidence_rationale":"Tier 3 — single-lab cell culture study without pathway-level genetic controls","pmids":["37740877"],"is_preprint":false}],"current_model":"TACR1 (NK-1R) is a seven-transmembrane Gq-coupled GPCR for substance P and related tachykinins whose extracellular N-terminus and first/second extracellular loops mediate high-affinity peptide binding, while transmembrane helix 5 (His197) forms a distinct binding pocket for non-peptide antagonists; after agonist stimulation the receptor activates PKC and ERK via phospholipase C, signals from lipid-raft/caveolar microdomains at the plasma membrane, undergoes clathrin/dynamin/β-arrestin-dependent endocytosis that is required for sustained cytosolic PKC and nuclear ERK activation underlying prolonged pain, and is routed post-endocytically toward lysosomal degradation via C-terminal tail interactions with SNX1/GASP; the full-length and truncated isoforms (differing by 96 C-terminal residues) couple differentially to effectors, with the truncated form found in monocytes signaling through CCR5 crosstalk/ERK2 rather than Ca²⁺ mobilization; tonic NK1R activity in the CNS maintains prefrontal dopaminergic tone and noradrenergic α2a-autoreceptor sensitivity, and defined Tacr1-expressing spinal and parabrachial circuits mediate sustained pain while RVM Tacr1+ ON cells suppress itch."},"narrative":{"teleology":[{"year":1991,"claim":"Molecular cloning of TACR1 established it as a Gq/PLC-coupled GPCR that binds substance P with sub-nanomolar affinity and triggers IP3 production, resolving the molecular identity of the pharmacologically defined NK-1 receptor.","evidence":"cDNA cloning and heterologous expression in COS-7 cells with radioligand binding and IP3 assays, independently in two laboratories","pmids":["1657150","1718267"],"confidence":"High","gaps":["Downstream signaling beyond IP3 not characterized","No structural information on ligand-receptor interaction","Receptor trafficking after activation unknown"]},{"year":1992,"claim":"Identification of two alternatively spliced isoforms (full-length and truncated) and systematic mutagenesis of extracellular domains defined the structural basis for peptide agonist binding and revealed that the C-terminal tail is required for high-affinity coupling and full signaling efficacy.","evidence":"Gene structure determination (5 exons), chimeric receptor/mutagenesis approaches, heterologous expression in COS cells and Xenopus oocytes with binding and electrophysiology","pmids":["1310144","1280161","1281469","1312928"],"confidence":"High","gaps":["Physiological relevance of the truncated isoform unknown","Antagonist binding site not yet mapped","No in vivo isoform-specific data"]},{"year":1993,"claim":"Identification of His197 in TM5 as essential for non-peptide antagonist binding demonstrated that agonist and antagonist binding pockets are spatially distinct, opening a structural framework for drug design.","evidence":"Site-directed mutagenesis with structure-activity analysis of CP 96345 analogues","pmids":["8384323"],"confidence":"High","gaps":["No three-dimensional structure available","Whether other TM residues contribute to the antagonist pocket not fully mapped","Mechanism of antagonist-induced conformational change unknown"]},{"year":1998,"claim":"NK1R knockout mice and a placebo-controlled clinical trial of MK-869 established that NK1R mediates central sensitization (wind-up) in pain and participates in mood regulation through a monoamine-independent mechanism, broadening the receptor's role beyond nociception.","evidence":"Targeted gene knockout with behavioral and electrophysiological phenotyping; randomized placebo-controlled clinical trial for depression; preclinical vocalization assays","pmids":["9537323","9733503"],"confidence":"High","gaps":["Monoamine-independent mechanism of antidepressant action not molecularly defined","Whether NK1R signaling in mood uses the same PLC/PKC cascade as in pain unknown","Circuit-level locus of NK1R's antidepressant action not identified"]},{"year":2003,"claim":"Mapping of isoform-specific expression in human brain (full-length dominant in locus coeruleus, ventral striatum) and identification of endokinins A/B as additional high-affinity endogenous agonists expanded the ligand-receptor framework and linked regional isoform distribution to mood and stress functions.","evidence":"TaqMan PCR and in situ hybridization in human brain; radioligand competition binding and hemodynamic assays for endokinins","pmids":["12752772","12716968"],"confidence":"High","gaps":["Whether endokinins and SP activate distinct downstream pathways via NK1R unknown","Isoform-specific signaling in native brain tissue not demonstrated","NK1R role in emesis (brainstem) characterized pharmacologically but not genetically"]},{"year":2004,"claim":"Demonstration that NK1R resides in lipid rafts/caveolae and that raft integrity is required for PKC translocation, together with identification of SNX1/GASP as C-terminal tail interactors directing post-endocytic lysosomal sorting, defined the membrane-microdomain and trafficking framework for NK1R signaling.","evidence":"Sucrose gradient fractionation, cholesterol depletion/rescue, PKC translocation assays; systematic GST pull-down and SPR kinetics for C-tail interactors","pmids":["15590676","15452121"],"confidence":"High","gaps":["Whether raft localization is required in neurons (not just HEK293/HepG2) unknown","Relative contribution of SNX1 vs GASP to degradation vs recycling not resolved","Relationship between raft-dependent signaling and endosomal signaling not established"]},{"year":2007,"claim":"NK1R knockout mice revealed that tonic NK1R signaling maintains noradrenergic and dopaminergic tone by sustaining α2a-autoreceptor sensitivity in locus coeruleus and dopamine efflux in prefrontal cortex, providing a mechanistic basis for the antidepressant and ADHD-like phenotypes of NK1R loss.","evidence":"In vivo microdialysis for noradrenaline and dopamine in freely moving NK1R−/− mice; [³⁵S]GTPγS autoradiography for α2a coupling; psychostimulant challenge","pmids":["17331215","19204064"],"confidence":"High","gaps":["Direct synaptic mechanism by which NK1R regulates α2a-autoreceptor sensitivity not defined","Whether dopaminergic and noradrenergic phenotypes share a common upstream mechanism unknown","Translation to human neurochemistry not demonstrated"]},{"year":2008,"claim":"Discovery that monocytes express exclusively the truncated NK1R isoform, which signals through ERK2 and CCR5 crosstalk rather than Ca²⁺ mobilization, established isoform-specific signaling as a general principle with immunological relevance.","evidence":"Flow cytometry, RT-PCR, Ca²⁺ imaging, chemotaxis, and ERK1/2 phosphorylation in human monocytes; rescue by full-length transfection","pmids":["18835883"],"confidence":"High","gaps":["Structural basis for truncated isoform's selective ERK2 activation unknown","Whether CCR5 and NK1R-T physically heterodimerize not determined","In vivo immune consequences of isoform-specific signaling not tested"]},{"year":2017,"claim":"Demonstration that NK1R signals from endosomes (not only the plasma membrane) to produce sustained PKC/ERK activation and prolonged pain established endosomal signaling as the pharmacologically relevant compartment and inspired endosome-targeted antagonist design.","evidence":"Pharmacological/genetic disruption of clathrin, dynamin, β-arrestin in spinal cord slices and in vivo pain models; cholestanol-conjugated antagonists targeting endosomal membranes","pmids":["28566424"],"confidence":"High","gaps":["Whether endosomal signaling also underlies NK1R's roles in emesis and mood not tested","Endosomal signaling pathway components beyond PKC/ERK not characterized","Truncated isoform's endosomal signaling capacity unknown"]},{"year":2021,"claim":"Circuit-level studies using Tacr1-Cre genetics identified a spinoparabrachial Tacr1+ projection essential for sustained (but not acute) pain and RVM Tacr1+ ON cells that suppress itch, dissociating NK1R-defined circuits for pain and itch modulation.","evidence":"Chemogenetics, optogenetics, optotagging in Tacr1-Cre mice; behavioral nociception and itch assays","pmids":["33591273","35972457"],"confidence":"High","gaps":["Molecular signaling within Tacr1+ parabrachial neurons not characterized","Whether the same or different SP sources drive the pain and itch circuits unknown","Human translational evidence for these circuits lacking"]},{"year":2021,"claim":"NK1R was placed upstream of PKCδ→NLRC4 inflammasome-driven neuronal pyroptosis after intracerebral hemorrhage, extending its neuroinflammatory role to a defined cell-death pathway.","evidence":"Mouse ICH model with aprepitant, NK1R agonist reversal, PKCδ agonist reversal, NLRC4 siRNA epistasis; Western blot for pyroptosis markers","pmids":["34244927","35922848"],"confidence":"Medium","gaps":["Single-lab findings not independently replicated","Whether this pyroptosis pathway operates in non-hemorrhagic neuroinflammation unknown","Direct physical interaction between NK1R signaling components and NLRC4 not shown"]},{"year":null,"claim":"Key open questions include the structural basis for isoform-specific signaling, the contribution of endosomal versus plasma membrane signaling to non-nociceptive NK1R functions (mood, emesis, immune), and whether endokinin versus substance P agonism activates distinct downstream programs.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of agonist-bound full-length NK1R in a lipid bilayer","Endosomal signaling paradigm untested outside pain","Isoform-selective pharmacology not developed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[16,19]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,6,13]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[14,26]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[26]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,13,17,26]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[7,8,19,28,31]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,29,30]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[30]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[7,28]}],"complexes":[],"partners":["SNX1","GASP1","NSF","ARRB1","CCR5","TAC1","TAC4"],"other_free_text":[]},"mechanistic_narrative":"TACR1 (NK-1R) is a Gq-coupled seven-transmembrane receptor for substance P and related tachykinins that transduces nociceptive, emetic, affective, and neuroinflammatory signals across central and peripheral tissues. The receptor binds peptide agonists via its N-terminal domain and first/second extracellular loops, while non-peptide antagonists occupy a distinct transmembrane pocket centered on His197 in TM5; after agonist stimulation it activates phospholipase C/PKC signaling from lipid-raft microdomains at the plasma membrane and, following clathrin/dynamin/β-arrestin–dependent endocytosis, sustains cytosolic PKC and nuclear ERK activation from endosomes to drive prolonged nociceptive excitation [PMID:1657150, PMID:8384323, PMID:15590676, PMID:28566424]. Alternative splicing produces a full-length isoform that predominates in the brain and supports high-affinity binding, Ca²⁺ mobilization, and receptor internalization, and a truncated isoform lacking 96 C-terminal residues that predominates in peripheral tissues and monocytes and signals through ERK2 and CCR5 crosstalk rather than canonical Ca²⁺ pathways [PMID:1310144, PMID:18835883, PMID:12752772]. Genetic ablation or pharmacological blockade of NK1R abolishes central sensitization and wind-up in spinal pain circuits, suppresses emesis, reduces alcohol reward, and produces antidepressant-like effects by elevating prefrontal noradrenergic and dopaminergic tone, while defined Tacr1-expressing spinoparabrachial and RVM circuits selectively mediate sustained pain and suppress itch [PMID:9537323, PMID:9733503, PMID:19204064, PMID:33591273, PMID:35972457]."},"prefetch_data":{"uniprot":{"accession":"P25103","full_name":"Substance-P receptor","aliases":["NK-1 receptor","NK-1R","Tachykinin receptor 1"],"length_aa":407,"mass_kda":46.3,"function":"Receptor for the tachykinin substance P, also able to bind and respond to tachynins neurokinin A/substance K and neurokinin B/neuromedin-K (PubMed:1718267, PubMed:15452552). The rank order of affinity of this receptor to tachykinins is: substance P > neurokinin A/substance K > neurokinin B/neuromedin-K (PubMed:1718267). Substance P binding to its receptor triggers G protein-coupled receptor signaling via activation of phosphatidylinositol hydrolysis by phospholipase C. Substance P binding also triggers signaling via activation of adenylate cyclase activity which results in increased intracellular levels of cyclic AMP (cAMP) (By similarity)","subcellular_location":"Cell membrane; Early endosome","url":"https://www.uniprot.org/uniprotkb/P25103/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TACR1","classification":"Not Classified","n_dependent_lines":19,"n_total_lines":1208,"dependency_fraction":0.015728476821192054},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TACR1","total_profiled":1310},"omim":[{"mim_id":"612636","title":"UNC80 HOMOLOG, NALCN CHANNEL COMPLEX SUBUNIT; UNC80","url":"https://www.omim.org/entry/612636"},{"mim_id":"611549","title":"SODIUM LEAK CHANNEL, NONSELECTIVE; NALCN","url":"https://www.omim.org/entry/611549"},{"mim_id":"607189","title":"REGULATOR OF G PROTEIN SIGNALING 8; RGS8","url":"https://www.omim.org/entry/607189"},{"mim_id":"604254","title":"DYSLEXIA, SUSCEPTIBILITY TO, 3; DYX3","url":"https://www.omim.org/entry/604254"},{"mim_id":"162323","title":"TACHYKININ RECEPTOR 1; TACR1","url":"https://www.omim.org/entry/162323"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Centrosome","reliability":"Approved"},{"location":"Basal body","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adipose tissue","ntpm":6.2}],"url":"https://www.proteinatlas.org/search/TACR1"},"hgnc":{"alias_symbol":["SPR","NK1R","NKIR"],"prev_symbol":["TAC1R"]},"alphafold":{"accession":"P25103","domains":[{"cath_id":"1.20.1070.10","chopping":"28-227_234-304","consensus_level":"high","plddt":91.0547,"start":28,"end":304},{"cath_id":"-","chopping":"309-342","consensus_level":"medium","plddt":69.3456,"start":309,"end":342}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P25103","model_url":"https://alphafold.ebi.ac.uk/files/AF-P25103-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P25103-F1-predicted_aligned_error_v6.png","plddt_mean":78.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TACR1","jax_strain_url":"https://www.jax.org/strain/search?query=TACR1"},"sequence":{"accession":"P25103","fasta_url":"https://rest.uniprot.org/uniprotkb/P25103.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P25103/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P25103"}},"corpus_meta":[{"pmid":"17337300","id":"PMC_17337300","title":"SPR microscopy and its applications to high-throughput analyses of biomolecular binding events and their kinetics.","date":"2007","source":"Biomaterials","url":"https://pubmed.ncbi.nlm.nih.gov/17337300","citation_count":220,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"17979772","id":"PMC_17979772","title":"SPR-based fragment screening: advantages and applications.","date":"2007","source":"Current topics in medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17979772","citation_count":134,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15053580","id":"PMC_15053580","title":"Direct detection of genomic DNA by enzymatically amplified SPR imaging measurements of RNA microarrays.","date":"2004","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/15053580","citation_count":132,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11742144","id":"PMC_11742144","title":"Comparison of the phenotype of NK1R-/- mice with pharmacological blockade of the substance P (NK1 ) receptor in assays for antidepressant and anxiolytic drugs.","date":"2001","source":"Behavioural pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/11742144","citation_count":129,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"18809310","id":"PMC_18809310","title":"High-throughput SPR sensor for food safety.","date":"2008","source":"Biosensors & bioelectronics","url":"https://pubmed.ncbi.nlm.nih.gov/18809310","citation_count":87,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"29896303","id":"PMC_29896303","title":"MMP1/PAR1/SP/NK1R paracrine loop modulates early perineural invasion of pancreatic cancer cells.","date":"2018","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/29896303","citation_count":80,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30348366","id":"PMC_30348366","title":"Ultra-sensitive detection by metal nanoparticles-mediated enhanced SPR biosensors.","date":"2018","source":"Talanta","url":"https://pubmed.ncbi.nlm.nih.gov/30348366","citation_count":77,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"10356644","id":"PMC_10356644","title":"Expression, regulation, and function of the SPR family of proteins. 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chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15590676","citation_count":91,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":45388,"output_tokens":5704,"usd":0.110862},"stage2":{"model":"claude-opus-4-6","input_tokens":9296,"output_tokens":4067,"usd":0.222232},"total_usd":0.713144,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":58117,"output_tokens":9318,"usd":0.15706},"round2_rules_fired":"R2,R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":12682,"output_tokens":3410,"usd":0.22299}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"Human peripheral blood monocytes express the truncated isoform of NK1R (NK1R-T) but not the full-length isoform (NK1R-F). NK1R-T does not mobilize calcium upon substance P (SP) stimulation alone, but enhances CCL5-induced calcium mobilization and chemotaxis in an ERK1/2-dependent manner. NK1R-T selectively activates ERK2 and promotes serine phosphorylation of CCR5, indicating crosstalk between NK1R-T and CCR5 at the receptor level.\",\n      \"method\": \"Transfection of NK1R-F into monocytes, calcium mobilization assays, chemotaxis assays, ERK1/2 phosphorylation assays, CCR5 phosphorylation assays, NK1R antagonist (aprepitant) inhibition\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Ca2+ mobilization, chemotaxis, kinase phosphorylation, receptor phosphorylation) in a single study with specific antagonist controls\",\n      \"pmids\": [\"18835883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"IL-1β upregulates NK-1R expression in human astroglioma cells and primary rat astrocytes at both mRNA and protein levels via NF-κB activation. The IL-1β-induced NK-1R is functional, as demonstrated by increased cytosolic Ca2+ response to SP stimulation; this response is blocked by the NK-1R antagonist CP-96,345. The NF-κB inhibitor CAPE blocks both IL-1β-induced NF-κB promoter activation and NK-1R gene expression.\",\n      \"method\": \"mRNA and protein expression analysis, calcium mobilization assay, pharmacological inhibition (CP-96,345, CAPE), NF-κB promoter reporter assay\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking NF-κB to functional NK1R upregulation with specific inhibitor controls\",\n      \"pmids\": [\"15390113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-12 and IL-18 induce NK-1R expression on murine splenic T cells through NF-κB activation (not requiring protein synthesis or the Stat4 pathway). IL-10 blocks this NK-1R induction, while TGF-β does not, placing SP/NK1R as part of the Th1 immune pathway promoting IFN-γ synthesis.\",\n      \"method\": \"mRNA expression analysis, actinomycin D and cycloheximide treatment, NF-κB inhibition, Stat4-/- mice, IL-10 and TGF-β co-treatment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (knockout mice) and pharmacological epistasis with multiple cytokine interventions establishing NF-κB pathway dependence\",\n      \"pmids\": [\"12734344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NK1R-/- mice lacking functional substance P-preferring receptors show reduced spontaneous dopamine efflux in the prefrontal cortex (>50% reduction) and abolished striatal dopamine response to d-amphetamine, demonstrating that NK1R regulates dopaminergic transmission in these brain regions. Pharmacological blockade with NK1R antagonist L-760735 mimics this hyperactivity phenotype, confirming a direct (non-developmental) receptor role.\",\n      \"method\": \"In vivo microdialysis, locomotor activity measurement, NK1R antagonist administration, NK1R-/- mice\",\n      \"journal\": \"Journal of psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo microdialysis in both KO and antagonist-treated animals with replicated pharmacological and genetic evidence\",\n      \"pmids\": [\"19204064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NK1R-/- mice have two-to-fourfold greater basal extracellular noradrenaline in the frontal cortex compared to wildtypes. Alpha2a-autoreceptor function is impaired in NK1R-/- mice, as shown by reduced [35S]GTPγS binding to activated alpha2a-adrenoceptors (-70%) in the locus coeruleus, without differences in noradrenaline transporter protein levels. This establishes NK1R as a regulator of somatodendritic alpha2a-adrenoceptor function modulating noradrenergic tone.\",\n      \"method\": \"In vivo microdialysis, retrodialysis, [35S]GTPγS binding assay, Western blot for noradrenaline transporter, alpha2-adrenoceptor antagonist (RX 821002) administration\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (microdialysis, GTPγS binding, Western blot) in NK1R-/- vs. wildtype mice\",\n      \"pmids\": [\"17331215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"NK1R-/- mice lack the caudal grooming and scratching response to the NK1 agonist GR73632 (confirming genetic ablation of the receptor), and display antidepressant-like behavior in the resident-intruder and forced swim tests similar to fluoxetine-treated animals. Acute pharmacological blockade with NK1R antagonists (L-760735, GR205171) broadly phenocopies the genetic knockout for antidepressant-relevant behaviors but not all behaviors, suggesting some phenotypes are developmental.\",\n      \"method\": \"Behavioral pharmacology (resident-intruder, forced swim test, tail suspension test, elevated plus-maze), NK1R-/- mice, NK1R antagonist treatment, NK1 agonist challenge\",\n      \"journal\": \"Behavioural pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic comparison of genetic knockout and pharmacological blockade with multiple behavioral readouts and cross-species validation\",\n      \"pmids\": [\"11742144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NK1R-deficient mice show reduced voluntary alcohol consumption and blunted alcohol conditioned place preference (in a gene dose-dependent manner). The NK1R antagonist L-703,606 dose-dependently suppresses alcohol intake in wildtype mice but is ineffective in NK1R KO mice, establishing receptor specificity. NK1R inactivation also prevents escalation of alcohol intake after repeated deprivation-access cycles.\",\n      \"method\": \"Two-bottle free-choice drinking, conditioned place preference, deprivation-escalation model, NK1R antagonist (L-703,606), NK1R KO mice\",\n      \"journal\": \"Psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — receptor specificity confirmed by failure of antagonist effect in KO mice; multiple behavioral models with gene dose-response\",\n      \"pmids\": [\"20112009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Genetic variation at the Tacr1 locus (-1372G/C SNP) elevates Tacr1 promoter transcriptional activity via altered binding of transcription factors GATA-2 and E2F-1 (demonstrated by EMSA and luciferase reporter assay), leading to elevated NK1R expression in the prefrontal cortex and amygdala of alcohol-preferring P-rats and increased sensitivity to NK1R antagonist-mediated reduction of alcohol self-administration. Central amygdala (but not prefrontal cortex) NK1R blockade replicates systemic antagonist effects.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA), luciferase reporter assay, Tacr1 mRNA quantification, NK1R radioligand binding, operant alcohol self-administration, intra-amygdala antagonist infusion\",\n      \"journal\": \"Biological psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — EMSA and reporter assay establishing functional promoter variant, combined with receptor binding and behavioral pharmacology\",\n      \"pmids\": [\"23419547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Spinal microglia activation is required for stress-induced visceral hyperalgesia and NK1R upregulation in the spinal cord. Minocycline (microglia inhibitor) blocks both stress-induced NK1R upregulation and hyperalgesia, while the p38 MAPK inhibitor SB203580 blocks hyperalgesia and NF-κB activation but not NK1R upregulation. Phospho-p38 colocalizes with OX42-positive microglia and neurons in the dorsal horn, placing microglial p38/NF-κB signaling upstream of visceral pain but not NK1R transcriptional upregulation.\",\n      \"method\": \"Western blot, immunostaining, immunoblotting, intrathecal drug administration, visceromotor response to colorectal distention, minocycline and SB203580 treatment, fractalkine injection\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection of microglia-NK1R axis with multiple inhibitors and functional behavioral readouts\",\n      \"pmids\": [\"19249394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A subset of spinal cord neurons expressing Tacr1 (NK1R) projects to a cluster of neurons in the superior lateral parabrachial nucleus (PBN-SL) that also express Tacr1. Chemogenetic activation of Tacr1-expressing spinal neurons evokes a full repertoire of somatotopically directed pain behaviors; PBN-SLTacr1 neurons respond to sustained but not acute noxious stimuli. Silencing PBN-SLTacr1 neurons causes mice to ignore long-lasting noxious stimuli but not acute pain, and activation of PBN-SLTacr1 neurons heightens nocifensive behaviors and suppresses itch.\",\n      \"method\": \"Chemogenetic activation/silencing (DREADDs), circuit tracing, calcium imaging, behavioral testing (ongoing vs. acute pain, itch models), optogenetics\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with chemogenetics, circuit tracing, and multiple behavioral readouts establishing spinoparabrachial NK1R circuit function\",\n      \"pmids\": [\"33591273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Tacr1-expressing ON cells in the rostral ventromedial medulla (RVM) exert inhibitory control over spinal pruriceptive transmission. Intramedullary substance P potentiates ON cell activity and reduces pruritogen-evoked scratching while producing mild mechanical sensitization. Chemogenetic activation of RVM Tacr1-expressing neurons reduces acute pruritogen-evoked scratching. Optotagging confirms RVM Tacr1-expressing neurons are ON cells.\",\n      \"method\": \"Intramedullary SP microinjection, chemogenetics (DREADDs), optotagging electrophysiology, scratching behavior assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — chemogenetic gain-of-function, electrophysiological cell identification, and behavioral readouts establishing NK1R ON-cell function in descending itch modulation\",\n      \"pmids\": [\"35972457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In pancreatic cancer perineural invasion, MMP1 activates PAR1 on dorsal root ganglia neurons to release substance P, which activates NK1R on pancreatic ductal adenocarcinoma (PDAC) cells, enhancing cellular migration, invasion, and perineural invasion via the SP/NK1R/ERK signaling axis. NK1R antagonism inhibits perineural invasion in vitro and in vivo.\",\n      \"method\": \"Matrigel/DRG in vitro PNI system, sciatic nerve invasion mouse model, MMP1 shRNA silencing, PAR1 and NK1R antagonist treatment, ERK pathway analysis, MRI with iron oxide nanoparticles\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (shRNA) and pharmacological intervention in both in vitro and in vivo models with defined signaling pathway (ERK)\",\n      \"pmids\": [\"29896303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Substance P activates both contractile and inflammatory signaling in lymphatic muscle cells through NK1R and NK3R. SP increases phosphorylation of MLC20 (contractile) and p38-MAPK and ERK1/2 (pro-inflammatory). Inhibition of ERK1/2 decreases p-MLC20 in a PKC-dependent manner, indicating crosstalk between the two pathways downstream of SP/NK1R and NK3R activation.\",\n      \"method\": \"Rat mesenteric lymphatic muscle cell culture, pharmacological inhibition of NK1R, NK3R, ERK1/2, PKC; phosphorylation assays (MLC20, p38-MAPK, ERK1/2)\",\n      \"journal\": \"Microcirculation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological inhibitors with defined signaling readouts, single lab study\",\n      \"pmids\": [\"21166923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"An antibody raised against a linear peptide from the third extracellular region (ECR-3) of rat brain NK1-R detects a 53-54 kDa band by Western blot of brain membranes and isolates 54 and 44 kDa species by affinity chromatography. Radiolabeled SP binds C6 astrocytes (which express NK1-R but not NK2-R or NK3-R) with Kd = 0.32 nM, and the anti-ECR-3 antibody inhibits this binding by >95%, confirming that the ECR-3 is accessible on the cell surface and functionally important for SP binding.\",\n      \"method\": \"Peptide-affinity antibody generation, Western blot, affinity chromatography, [125I]-SP radioligand binding assay, antibody competition assay\",\n      \"journal\": \"Journal of neuroimmunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — radioligand binding with antibody competition establishes ECR-3 surface accessibility and SP binding site; single lab study\",\n      \"pmids\": [\"8707930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NK1R inhibition with aprepitant promotes hematoma clearance after intracerebral hemorrhage by shifting microglia toward M2 polarization via downregulation of the PKC/p38MAPK/NFκB signaling pathway. NK1R agonist (GR73632) or PKC agonist (PMA) reverses this effect. Thrombin upregulates substance P and is identified as a key upstream mediator of NK1R activation in this context.\",\n      \"method\": \"Intracerebroventricular NK1R agonist and PKC agonist injection, intraperitoneal aprepitant, thrombin injection, Western blot, immunofluorescence, hemoglobin measurement, behavioral testing\",\n      \"journal\": \"Neurotherapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological gain and loss of function with pathway rescue experiments, single lab study\",\n      \"pmids\": [\"34244927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NK1R activation after intracerebral hemorrhage mediates neuronal pyroptosis through the NK1R/PKCδ/NLRC4 signaling pathway. Aprepitant (NK1R antagonist) reduces NLRC4, cleaved-caspase-1, GSDMD, IL-1β, and IL-18 expression. NK1R agonist or PKCδ agonist reverses neuroprotective effects of aprepitant, and NLRC4 siRNA knockdown phenocopies aprepitant neuroprotection.\",\n      \"method\": \"Intracerebroventricular NK1R agonist (GR73632), PKCδ agonist (PMA), NLRC4 siRNA, Western blot, immunofluorescence, neurobehavioral testing\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown, pharmacological agonist/antagonist rescue experiments establishing pathway order, single lab\",\n      \"pmids\": [\"35922848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Glioblastoma cell lines differ markedly in the ratio of full-length to truncated NK1R isoform expression. Significant SP conjugate binding, internalization, and cell killing by a saporin-SP toxin conjugate are only observed in cell lines expressing high full-length NK1R (LN319), not in those with predominantly truncated isoforms, establishing that the full-length NK1R isoform is required for productive SP internalization and targeted cell killing.\",\n      \"method\": \"RNA expression analysis of NK1R isoforms, radiolabeled SP binding ([177Lu]-SP), fluorescence-labeled SP internalization (SP-FAM), saporin-SP toxin cytotoxicity assay\",\n      \"journal\": \"Cancer biotherapy & radiopharmaceuticals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal SP binding/internalization methods correlating isoform expression with functional outcomes, single lab\",\n      \"pmids\": [\"24552486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In esophageal squamous cell carcinoma cells, SP/NK1R signaling promotes cell proliferation through upregulation of Hes1 (Hairy and Enhancer of Split 1). NK1R downregulation reduces Hes1 expression and suppresses clonogenic growth and tumor formation in nude mice.\",\n      \"method\": \"iTRAQ proteomics, CCK-8 proliferation assay, colony formation assay, xenograft tumor model, Western blot, RT-qPCR\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics-guided pathway identification with in vitro and in vivo validation; single lab but multiple methods\",\n      \"pmids\": [\"31109645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SP/NK1R axis activation in MCF-7 breast cancer cells induces ROS accumulation and upregulates NF-κB and its downstream pro-inflammatory cytokines (TNF-α, IL-6). NK1R blockade with aprepitant reduces cell viability at least partly through p53-mediated upregulation of p21, reduces intracellular ROS, and attenuates the oncogenic properties of SP.\",\n      \"method\": \"Resazurin cell viability assay, ROS assay (H2DCFDA), qRT-PCR gene expression analysis\",\n      \"journal\": \"Cell biochemistry and biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, pharmacological intervention only without genetic controls or pathway rescue\",\n      \"pmids\": [\"37740877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In cervical cancer (HeLa) cells, the truncated isoform of NK1R (NK1R-Tr) is the dominant form expressed. SP increases HeLa cell proliferation and upregulates cyclin B1 and Bcl-2 while downregulating p21 and Bax; it also promotes migration and increases MMP-2/MMP-9 expression. Aprepitant reverses all these effects and induces G2 arrest and apoptosis.\",\n      \"method\": \"MTT assay, qRT-PCR, flow cytometry, wound-healing assay\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, pharmacological intervention without genetic confirmation of isoform-specific signaling\",\n      \"pmids\": [\"34766230\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TACR1 (NK1R) is a G protein-coupled receptor for substance P (and related tachykinins) that exists in full-length and truncated isoforms with distinct signaling capacities: the full-length isoform couples to calcium mobilization and supports ligand internalization, while the truncated isoform selectively activates ERK signaling and modulates chemokine receptor (CCR5) crosstalk in monocytes; downstream of receptor activation, NK1R signals through PKC, p38MAPK, ERK1/2, and NF-κB to regulate neurogenic inflammation, dopaminergic and noradrenergic neurotransmission, spinal pain and itch processing via a spinoparabrachial circuit and descending RVM ON-cell pathway, alcohol reward behavior, and cancer cell proliferation/migration, with receptor expression itself regulated transcriptionally by NF-κB in response to IL-1β, IL-12, and IL-18.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from KEEP papers.\n\n**Classification summary:**\n- Most of the 100 retrieved papers are about SPR (surface plasmon resonance) biosensor technology — EXCLUDE (alias collision: \"SPR\" = Surface Plasmon Resonance, not TACR1)\n- Papers [4], [6], [11-14], [16-18], [24], [26], [28-29], [34-35], [41], [48-50], [55], [58], [60], [63-64], [67-68], [70-72], [76-79], [83], [89]: about TACR1/NK1R — KEEP\n- Paper [8]: about SPR (small proline-rich) genes — EXCLUDE\n- Paper [46]: C. elegans spr-1/CoREST — EXCLUDE (different gene)\n- Paper [52]: E. coli spr — EXCLUDE (different gene)\n- Paper [62]: spr-/- mice = sepiapterin reductase knockout — EXCLUDE (different gene)\n- Papers [28 lncRNA]: about lncRNA RMRP/TACR1 axis — borderline; the TACR1 protein signaling is described as downstream target, KEEP for the ERK pathway finding\n\n**gene2pubmed curated papers:**\n- [4] PMID:9733503 — KEEP (NK1R antidepressant mechanism)\n- [7] PMID:9537323 — KEEP (NK1R knockout, nociception)\n- [11] PMID:1310144 — KEEP (two isoforms, differential signaling)\n- [12] PMID:8384323 — KEEP (His197 binding site)\n- [13] PMID:1657150 — KEEP (human NK-1 gene cloning)\n- [14] PMID:28566424 — KEEP (endosomal signaling)\n- [15] PMID:1718267 — KEEP (human SPR cloning)\n- [16] PMID:21091716 — KEEP (NK1R immune signaling review with mechanistic content)\n- [17] PMID:15452121 — KEEP (C-terminal tail interactions with SNX1, GASP, NSF)\n- [18] PMID:1280161 — KEEP (extracellular domain peptide binding)\n- [19] PMID:12752772 — KEEP (isoform distribution)\n- [20] PMID:1281469 — KEEP (agonist/antagonist binding domains)\n- [21] PMID:12716968 — KEEP (endokinins binding NK1R)\n- [22] PMID:23933301 — KEEP (SP/NK1R cancer signaling)\n- [24] PMID:1312928 — KEEP (gene structure)\n- [28] PMID:20008142 — KEEP (miRNA regulation of NK1R)\n- [29] PMID:12686752 — KEEP (brainstem NK1R in emesis)\n- [30] PMID:15590676 — KEEP (lipid raft localization)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1991,\n      \"finding\": \"The human substance P receptor (NK-1/TACR1) was cloned as a 407-amino-acid G-protein-coupled receptor; when expressed in COS-7 cells it binds substance P with Kd ~0.24–0.35 nM and its stimulation triggers rapid, transient inositol 1,4,5-trisphosphate production, establishing Gq/phospholipase C as its primary intracellular effector. The gene resides on human chromosome 2 as a single-copy locus.\",\n      \"method\": \"cDNA cloning, heterologous expression in COS-7 cells, radioligand binding, IP3 assay, chromosome mapping with mouse/human hybrids\",\n      \"journal\": \"Biochemistry / Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — independent cloning in two labs with functional reconstitution (IP3, radioligand binding) in the same year\",\n      \"pmids\": [\"1657150\", \"1718267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The human TACR1 gene contains five exons with intron positions conserved with the NK-2 (neuromedin K) receptor gene, consistent with evolution from a common ancestral GPCR gene. The gene spans ~60 kb.\",\n      \"method\": \"Genomic DNA cloning and sequencing, Southern blot, restriction mapping\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct genomic sequencing of the human locus\",\n      \"pmids\": [\"1312928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Two isoforms of the human NK-1 receptor (long and short/truncated) arise from alternative pre-mRNA splicing. The long form binds substance P with high affinity and activates oscillating Cl⁻ currents in Xenopus oocytes. The short form binds substance P with ≥10-fold lower affinity and elicits only weak electrophysiological responses, indicating the C-terminal cytoplasmic tail is required for full agonist coupling and signaling efficacy.\",\n      \"method\": \"cDNA cloning, heterologous expression in COS cells and Xenopus oocytes, radioligand binding, electrophysiology\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in two heterologous systems with pharmacological and electrophysiological readouts\",\n      \"pmids\": [\"1310144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The N-terminal extracellular domain of NK-1R is required for high-affinity peptide binding: mutagenesis of residues in the N-terminus reduced affinity for substance P, substance K, and a C-terminal SP analog, but not for a non-peptide antagonist. Val-97 in the second extracellular segment selectively influences neurokinin B affinity, implicating distinct extracellular determinants for peptide selectivity.\",\n      \"method\": \"Site-directed mutagenesis, heterologous expression in COS cells, radioligand competition binding\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with functional binding readout\",\n      \"pmids\": [\"1280161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Systematic extracellular domain substitutions revealed that three residues in the first extracellular segment and two in the second are required for optimal binding of all three natural tachykinin peptide agonists; the third and fourth extracellular segments partially determine NK-1R subtype selectivity of the non-peptide antagonist L-703,606, showing that agonist and antagonist binding domains are spatially distinct.\",\n      \"method\": \"Chimeric receptor construction, mutagenesis, heterologous expression, radioligand competition binding\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with systematic chimeric/mutagenesis mapping\",\n      \"pmids\": [\"1281469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Histidine 197 in the fifth transmembrane helix of the human NK-1R forms an amino-aromatic interaction specifically with the benzhydryl moiety of the non-peptide antagonist CP 96345 but not with peptide agonists, defining a transmembrane antagonist-binding pocket distinct from the extracellular peptide-binding site.\",\n      \"method\": \"Site-directed mutagenesis, heterologous expression, radioligand binding, structure-activity analysis of antagonist analogues\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with orthogonal SAR validation; published in Nature\",\n      \"pmids\": [\"8384323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"An antibody targeting the third extracellular region (ECR-3) of rat brain NK1R blocked >95% of [¹²⁵I]-SP binding to intact C6 astrocytes and CHO cells expressing NK1R, confirming the third extracellular loop is surface-exposed and participates in ligand access. Immunoaffinity purification from rat brain yielded bands of ~54 kDa and ~44 kDa on SDS-PAGE.\",\n      \"method\": \"Peptide-immunized antibody generation, radioligand binding inhibition, Western blot, affinity purification from rat brain membranes\",\n      \"journal\": \"Journal of neuroimmunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional antibody blocking plus biochemical characterization; single lab\",\n      \"pmids\": [\"8707930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Genetic ablation of the NK-1 receptor (TACR1) in mice abolished wind-up amplification of nociceptive reflexes and intensity coding in the dorsal horn, demonstrating that NK-1R–mediated substance P signaling is required for the full development of central sensitization. NK-1R was also essential for stress-induced analgesia and aggression, but not for acute pain or hyperalgesia.\",\n      \"method\": \"Targeted gene knockout in mice, behavioral nociception assays (wind-up, tail-flick, hot-plate), electrophysiology of spinal dorsal horn neurons\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined electrophysiological and behavioral phenotypes; published in Nature\",\n      \"pmids\": [\"9537323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Blockade of central NK-1 receptors by the non-peptide antagonist MK-869 produced antidepressant effects in a placebo-controlled clinical trial, and in preclinical studies NK-1R antagonists suppressed isolation-induced vocalizations without interacting with monoamine systems in the manner of established antidepressants, establishing a monoamine-independent mechanism for NK-1R in mood regulation.\",\n      \"method\": \"Randomized placebo-controlled clinical trial; preclinical vocalization suppression assay; receptor binding and monoamine interaction studies\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clinical trial plus orthogonal preclinical mechanism studies; published in Science\",\n      \"pmids\": [\"9733503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"NK1R-/- mice phenocopied the behavioral effects of NK1R antagonists in antidepressant-relevant assays (forced swim, resident-intruder), and both genetic and pharmacological inactivation of NK1R did not produce sedation or motor impairment, validating that the antidepressant-like phenotype requires absence of functional NK1R signaling rather than developmental compensation.\",\n      \"method\": \"NK1R knockout mice vs. NK1R antagonists (L-760735, GR205171) in behavioral assays; central receptor occupancy confirmed by agonist-challenge test\",\n      \"journal\": \"Behavioural pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal genetic and pharmacological approaches in multiple species and assays\",\n      \"pmids\": [\"11742144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The long NK-1R isoform is the dominant form in human brain (quantified by TaqMan PCR), with highest levels in locus coeruleus and ventral striatum, whereas the truncated isoform predominates in peripheral tissues; ³H-SP autoradiography correlated with mRNA distribution, linking isoform-specific expression to region-specific functions in mood and stress circuits.\",\n      \"method\": \"Riboprobe in situ hybridization, quantitative TaqMan PCR, in vitro autoradiography with ³H-SP\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in human brain; strong anatomical-functional correlation\",\n      \"pmids\": [\"12752772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Substance P and the NK-1R in nucleus tractus solitarius and area postrema brainstem nuclei are critical mediators of the emetic reflex; NK-1R antagonists block emesis triggered by diverse stimuli (chemotherapy, motion, apomorphine) in animal models, placing NK-1R downstream of multiple emetic pathways converging on brainstem integrative nuclei.\",\n      \"method\": \"NK-1R antagonist pharmacology in ferret/cat emesis models; lesion and microinjection studies targeting brainstem nuclei\",\n      \"journal\": \"Journal of pharmacological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection across multiple emetic stimuli; single-lab review synthesis\",\n      \"pmids\": [\"12686752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Endokinins A and B (EKA/B), encoded by the tachykinin precursor 4 gene, display equivalent affinity for the NK-1 receptor as substance P and produce identical hemodynamic effects in rats, identifying them as additional endogenous agonists for TACR1 at peripheral SP receptors.\",\n      \"method\": \"Radioligand competition binding at NK-1R, in vivo hemodynamic measurements in rats\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct radioligand binding plus in vivo functional equivalence demonstrated\",\n      \"pmids\": [\"12716968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"NK-1R localizes to lipid rafts and caveolae at the plasma membrane; cholesterol depletion with methyl-β-cyclodextrin abolishes NK1R-mediated signaling. Upon substance P stimulation, activated PKC translocates from cytoplasm specifically to lipid rafts, demonstrating that raft integrity is required for productive NK1R–PKC coupling.\",\n      \"method\": \"Sucrose gradient fractionation, immunofluorescence, cholesterol depletion/replenishment assay, PKC translocation assay in HEK293 and HepG2 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — biochemical fractionation plus functional cholesterol-depletion rescue experiment; multiple cell lines\",\n      \"pmids\": [\"15590676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The C-terminal tail of NK-1R (truncated by 50 residues) retains interaction with both SNX1 (sorting nexin 1) and GASP (G protein-coupled receptor-associated sorting protein) as well as NSF, identifying an extended C-terminal binding epitope that directs post-endocytic trafficking of the receptor toward lysosomal degradation versus recycling pathways.\",\n      \"method\": \"GST pull-down library screen of 59 receptor C-terminal tails; SPR kinetics confirmation for selected hits; NK-1R truncation mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic GST pull-down across receptor library plus SPR kinetic validation and truncation mapping\",\n      \"pmids\": [\"15452121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"IL-1β upregulates NK-1R expression in human astroglioma cells and primary rat astrocytes at both mRNA and protein levels via NF-κB activation; the induced NK-1R is functional (SP triggers Ca²⁺ mobilization), and NF-κB inhibitor CAPE blocks both the promoter activation and the induction of NK-1R gene expression.\",\n      \"method\": \"Western blot, RT-PCR, Ca²⁺ imaging, NF-κB reporter assay, pharmacological inhibition in human astroglioma (U87 MG) and primary rat astrocytes\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (mRNA, protein, Ca²⁺ function, NF-κB reporter) in two cell models\",\n      \"pmids\": [\"15390113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NK1R-/- mice display elevated basal extracellular noradrenaline in frontal cortex (2–4× higher than wildtype) associated with desensitization/reduced GTPγS coupling of somatodendritic α2a-adrenoceptors in locus coeruleus, demonstrating that tonic NK1R signaling normally suppresses noradrenergic tone through α2a-autoreceptor regulation.\",\n      \"method\": \"In vivo microdialysis (anaesthetized and freely moving mice), [³⁵S]GTPγS autoradiography of locus coeruleus, Western blot for noradrenaline transporter, α2-antagonist pharmacology\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo microdialysis combined with receptor autoradiography and pharmacological validation; multiple readouts\",\n      \"pmids\": [\"17331215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human peripheral blood monocytes express exclusively the truncated NK-1R isoform (NK1R-T), which lacks the C-terminal 96-aa cytoplasmic domain. NK1R-T does not mobilize Ca²⁺ alone but enhances CCL5/CCR5-mediated Ca²⁺ mobilization and chemotaxis through ERK1/2 (selectively activating ERK2 alone), and induces serine phosphorylation of CCR5, revealing cross-receptor crosstalk at the receptor level.\",\n      \"method\": \"Flow cytometry, RT-PCR, Ca²⁺ imaging, chemotaxis assay, Western blot for ERK1/2 phosphorylation, CCR5 serine phosphorylation assay; NK1R-F transfection comparator\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods; isoform-specific effects confirmed by transfection rescue\",\n      \"pmids\": [\"18835883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Chronic stress-induced upregulation of spinal NK1R expression depends on microglial p38 MAPK activation; minocycline (microglia inhibitor) blocked both NK1R upregulation and visceral hyperalgesia, while the p38 inhibitor SB203580 blocked hyperalgesia without blocking NK1R upregulation, placing microglial activation upstream of spinal NK1R increase and dissociating the two downstream effects.\",\n      \"method\": \"Water-avoidance stress rat model, Western blot and immunostaining for NK1R/OX42/P-p38, intrathecal drug delivery, colorectal distension visceromotor response\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo epistasis with two pharmacological tools dissecting pathway; functional and biochemical readouts\",\n      \"pmids\": [\"19249394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NK1R-/- mice exhibit hyperactivity that is reversed by psychostimulants (d-amphetamine, methylphenidate), mirroring ADHD. In vivo microdialysis revealed >50% reduction in spontaneous dopamine efflux in prefrontal cortex and abolished striatal dopamine response to d-amphetamine in NK1R-/- mice, demonstrating that NK1R signaling tonically maintains dopaminergic tone in frontocortical and striatal circuits.\",\n      \"method\": \"Locomotor activity measurement, in vivo microdialysis (prefrontal cortex and striatum), NK1R antagonist (L-760735) pharmacology, psychostimulant challenge\",\n      \"journal\": \"Journal of psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo microdialysis with genetic and pharmacological convergent evidence; genotype–pharmacology interaction\",\n      \"pmids\": [\"19204064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NK1R-/- mice survive hyperoxia (90% O₂) significantly worse than wildtype (median survival 84 h vs. 120 h), with increased lung inflammation, edema, and apoptosis (TUNEL), demonstrating a paradoxical protective role for NK1R in hyperoxic lung injury. In cultured lung epithelial cells, exogenous SP promoted cell death under hyperoxia, revealing distinct tissue-level versus cell-autonomous signaling by the SP/NK1R axis.\",\n      \"method\": \"NK1R-/- and TRPV1-/- mouse hyperoxia model, BAL fluid analysis, TUNEL staining, metallothionein/Na-K-ATPase Western blot, cell culture SP treatment under hyperoxia\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype plus in vitro mechanistic follow-up; single lab\",\n      \"pmids\": [\"19633070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Prolonged exposure of NK1R to substance P decreases NK1R mRNA in bladder urothelium and upregulates specific miRNAs (miR-449b, miR-500, miR-328, miR-320) that directly correlate with NK1R mRNA/protein downregulation, identifying a miRNA-mediated negative feedback loop regulating NK1R expression.\",\n      \"method\": \"RT-PCR, Western blot, miRNA expression profiling, correlation analysis in cell models and human bladder biopsy specimens from BPS patients\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — expression correlation plus cell-based SP stimulation data; miRNA-NK1R link shown by correlation and cell model only\",\n      \"pmids\": [\"20008142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NK1R deletion or antagonism with L-703,606 reduces voluntary alcohol consumption and alcohol-conditioned place preference in a gene-dose-dependent manner; escalation of intake after repeated deprivation cycles occurs in wildtype but not NK1R-/- mice, identifying NK1R as a direct (non-developmental) regulator of alcohol reward and motivational escalation.\",\n      \"method\": \"Two-bottle free-choice intake, conditioned place preference, deprivation-escalation model in C57BL/6 NK1R-/- mice; NK1R antagonist receptor-specificity confirmed in KO\",\n      \"journal\": \"Psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — convergent genetic deletion and pharmacological receptor-specific blockade with multiple behavioral paradigms\",\n      \"pmids\": [\"20112009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Substance P activates both contractile (MLC₂₀ phosphorylation) and pro-inflammatory (p38-MAPK, ERK1/2) pathways in lymphatic muscle cells via NK1R and NK3R. ERK1/2 inhibition reduces p-MLC₂₀ in a PKC-dependent manner, demonstrating crosstalk between the inflammatory and contractile cascades downstream of SP receptor activation in lymphatics.\",\n      \"method\": \"Rat mesenteric lymphatic muscle cell culture, pharmacological inhibitors, Western blot for p-MLC₂₀, p-p38, p-ERK1/2, NK1R/NK3R expression confirmed by RT-PCR\",\n      \"journal\": \"Microcirculation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with multiple kinase readouts; single-lab cell culture model\",\n      \"pmids\": [\"21166923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Elevated Tacr1 expression in prefrontal cortex and central amygdala of alcohol-preferring (P) rats, driven in part by a -1372C allele that increases GATA-2/E2F-1 transcription factor binding and promoter activity, confers heightened sensitivity to NK1R antagonist (L822429) effects on alcohol self-administration; central amygdala infusion of L822429 replicates systemic effects, localizing NK1R's role in alcohol intake to this region.\",\n      \"method\": \"Operant self-administration, microinfusion, Tacr1 qPCR, NK1R autoradiography, Tacr1 promoter sequencing, EMSA, luciferase reporter assay\",\n      \"journal\": \"Biological psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — luciferase reporter + EMSA for promoter mechanism; microinfusion + behavioral readout for circuit localization; multiple orthogonal methods\",\n      \"pmids\": [\"23419547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NK-1R full-length and truncated isoforms are differentially expressed across glioblastoma cell lines; only cell lines with high full-length NK1R (e.g., LN319) show significant SP conjugate binding, receptor internalization, and targeted cell killing by saporin-SP toxin, establishing that full-length NK1R isoform expression is required for SP-mediated receptor internalization and targeted cytotoxicity.\",\n      \"method\": \"RT-PCR for isoform quantification, radioligand binding (¹⁷⁷Lu-SP), fluorescence-labeled SP internalization, saporin-SP cytotoxicity assay in 4 GBM cell lines\",\n      \"journal\": \"Cancer biotherapy & radiopharmaceuticals\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple assays across cell lines linking isoform to functional internalization; single lab\",\n      \"pmids\": [\"24552486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NK1R signals from endosomes (not only the plasma membrane) to produce sustained neuronal excitation and pain: after SP stimulation, NK1R undergoes clathrin/dynamin/β-arrestin–dependent endocytosis required for activation of cytosolic PKC and nuclear ERK as well as transcription. Endocytosis inhibitors block sustained spinal neuron excitation in vitro and nociception in vivo. Cholestanol-conjugated NK1R antagonists that target endosomal membranes provide more effective and prolonged antinociception than conventional antagonists.\",\n      \"method\": \"Pharmacological/genetic disruption of clathrin, dynamin, β-arrestin in spinal cord slice electrophysiology and in vivo pain models; cholestanol-conjugated antagonist synthesis and testing; PKC/ERK activation assays; mouse nociception models\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple genetic and pharmacological tools dissecting endosomal signaling; in vitro and in vivo functional validation; novel membrane-targeted drug strategy\",\n      \"pmids\": [\"28566424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In pancreatic cancer, MMP1 secreted by cancer cells activates PAR1 on dorsal root ganglion neurons, which then release substance P; SP activates NK1R on pancreatic cancer cells to enhance migration, invasion, and perineural invasion via SP/NK1R/ERK signaling. Silencing MMP1 or blocking NK1R or PAR1 inhibited perineural invasion in vitro and in vivo.\",\n      \"method\": \"Matrigel/DRG co-culture PNI model, sciatic nerve invasion mouse model, shRNA knockdown, NK1R/PAR1 antagonists, Western blot for p-ERK, MRI with iron oxide nanoparticles\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo models with genetic and pharmacological convergence; defined SP/NK1R/ERK pathway\",\n      \"pmids\": [\"29896303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A spinoparabrachial circuit defined by Tacr1 expression drives ongoing pain: Tacr1-expressing spinal projection neurons (NK1R+) target a small cluster of neurons in the superior lateral parabrachial nucleus (PBN-SL) that also express Tacr1; chemogenetic silencing of PBN-SLTacr1 neurons causes mice to ignore long-lasting noxious stimuli, while activation heightens nocifensive behavior and suppresses itch, establishing this circuit as essential for sustained (but not acute) pain processing.\",\n      \"method\": \"Chemogenetics (DREADD), optogenetics, optotagging to identify ON cells, Tacr1-Cre mouse intersectional genetics, behavioral nociception and itch assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic circuit-dissection tools (chemogenetics, optogenetics, optotagging) with defined behavioral phenotypes\",\n      \"pmids\": [\"33591273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NK1R inhibition with aprepitant after intracerebral hemorrhage promotes M2 microglial polarization and hematoma clearance by downregulating the PKC/p38MAPK/NFκB signaling pathway; NK1R agonist or PKC agonist reversed these effects, placing NK1R upstream of PKC/p38MAPK/NFκB in post-hemorrhagic neuroinflammation. Thrombin injection increased substance P, identifying thrombin as an upstream activator of the NK1R axis after ICH.\",\n      \"method\": \"Mouse ICH model (autologous blood injection), Western blot, immunofluorescence, intracerebroventricular NK1R agonist/PKC agonist reversal experiments, neurobehavioral testing\",\n      \"journal\": \"Neurotherapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological epistasis with agonist reversal experiments defining pathway order; in vivo model\",\n      \"pmids\": [\"34244927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"After intracerebral hemorrhage, NK1R activation drives NLRC4-dependent neuronal pyroptosis via a PKCδ-dependent pathway; aprepitant (NK1R antagonist) reduced NLRC4, cleaved-caspase-1, GSDMD, IL-1β and IL-18, and these neuroprotective effects were abolished by NK1R agonist GR73632 or PKCδ agonist PMA, while NLRC4 siRNA recapitulated aprepitant's effects, placing NK1R→PKCδ→NLRC4 as a sequential pyroptosis pathway.\",\n      \"method\": \"Mouse ICH model, Western blot, immunofluorescence, intracerebroventricular siRNA knockdown, agonist reversal experiments, neurobehavioral assays\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic (siRNA) and pharmacological epistasis in vivo defining sequential pathway; single lab\",\n      \"pmids\": [\"35922848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Tacr1-expressing ON cells in the rostral ventromedial medulla (RVM) exert inhibitory control over spinal pruriceptive transmission: intramedullary substance P potentiated RVM ON-cell firing and reduced pruritogen-evoked scratching while producing mild mechanical sensitization; chemogenetic activation of RVM Tacr1+ neurons reduced acute itch; optotagging confirmed Tacr1+ neurons are ON cells.\",\n      \"method\": \"Intramedullary microinjection of SP, chemogenetics (DREADD), optotagging electrophysiology in Tacr1-Cre mice, behavioral pruritogen scratching assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — chemogenetics plus optotagging plus pharmacology converge on same functional conclusion\",\n      \"pmids\": [\"35972457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Activation of the SP/NK1R axis in breast cancer MCF-7 cells drives ROS accumulation and NF-κB-mediated upregulation of pro-inflammatory cytokines (TNF-α, IL-6) while downregulating p21; aprepitant (NK1R antagonist) reverses these effects and induces p53-mediated p21 upregulation, placing NK1R upstream of the ROS/NF-κB/p53 axis controlling cancer cell proliferation.\",\n      \"method\": \"ROS assay (H2DCFDA), qRT-PCR, resazurin viability assay, SP and aprepitant dose-response in MCF-7 cells\",\n      \"journal\": \"Cell biochemistry and biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single-lab cell culture study without pathway-level genetic controls\",\n      \"pmids\": [\"37740877\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TACR1 (NK-1R) is a seven-transmembrane Gq-coupled GPCR for substance P and related tachykinins whose extracellular N-terminus and first/second extracellular loops mediate high-affinity peptide binding, while transmembrane helix 5 (His197) forms a distinct binding pocket for non-peptide antagonists; after agonist stimulation the receptor activates PKC and ERK via phospholipase C, signals from lipid-raft/caveolar microdomains at the plasma membrane, undergoes clathrin/dynamin/β-arrestin-dependent endocytosis that is required for sustained cytosolic PKC and nuclear ERK activation underlying prolonged pain, and is routed post-endocytically toward lysosomal degradation via C-terminal tail interactions with SNX1/GASP; the full-length and truncated isoforms (differing by 96 C-terminal residues) couple differentially to effectors, with the truncated form found in monocytes signaling through CCR5 crosstalk/ERK2 rather than Ca²⁺ mobilization; tonic NK1R activity in the CNS maintains prefrontal dopaminergic tone and noradrenergic α2a-autoreceptor sensitivity, and defined Tacr1-expressing spinal and parabrachial circuits mediate sustained pain while RVM Tacr1+ ON cells suppress itch.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TACR1 (NK1R) is a G protein-coupled receptor for substance P that transduces tachykinin signaling into diverse physiological outputs spanning nociception, affective behavior, neuromodulation, immune regulation, and tumor biology. The full-length receptor couples to intracellular calcium mobilization and undergoes ligand-driven internalization, whereas a truncated isoform (NK1R-T) selectively activates ERK1/2 and cross-talks with CCR5 to enhance chemokine-driven chemotaxis in monocytes [PMID:18835883, PMID:24552486]. Downstream, NK1R signals through PKC, p38 MAPK, ERK1/2, and NF-κB to regulate dopaminergic and noradrenergic neurotransmission, spinoparabrachial pain processing, descending inhibition of itch via RVM ON-cells, alcohol reward, microglial polarization after intracerebral hemorrhage, and cancer cell proliferation and invasion [PMID:19204064, PMID:17331215, PMID:33591273, PMID:35972457, PMID:20112009, PMID:34244927, PMID:29896303]. NK1R expression is itself transcriptionally upregulated by NF-κB in response to IL-1β, IL-12, and IL-18, creating a positive-feedback loop that amplifies neurogenic inflammation and Th1 immunity [PMID:15390113, PMID:12734344].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Establishing that the third extracellular region (ECR-3) of NK1R is surface-accessible and required for high-affinity substance P binding provided the first structural insight into ligand–receptor engagement.\",\n      \"evidence\": \"Peptide-directed antibody competition of [125I]-SP binding on C6 astrocytes expressing only NK1R\",\n      \"pmids\": [\"8707930\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab study; not validated with mutagenesis of the ECR-3 domain\", \"No crystal/cryo-EM structure of SP–NK1R complex available from this work\", \"Does not address whether ECR-3 contacts differ between tachykinin family members\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Genetic ablation of NK1R in mice produced antidepressant-like behavioral phenotypes, establishing for the first time that the SP/NK1R axis tonically regulates affective behavior in vivo.\",\n      \"evidence\": \"Behavioral pharmacology (forced swim, resident-intruder) in NK1R−/− mice vs. NK1R antagonist-treated wild-types\",\n      \"pmids\": [\"11742144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Some behavioral phenotypes were not mimicked by acute antagonist treatment, suggesting developmental contributions\", \"Neurotransmitter mechanisms mediating the antidepressant phenotype were not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating that IL-12 and IL-18 induce NK1R expression on T cells through NF-κB (independent of Stat4) placed NK1R transcription under direct control of the innate immune signaling axis and within the Th1 program.\",\n      \"evidence\": \"mRNA analysis in murine splenocytes with NF-κB inhibition, Stat4−/− mice, IL-10 co-treatment\",\n      \"pmids\": [\"12734344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact NF-κB binding sites in the TACR1 promoter were not mapped\", \"Relevance to human T cells not directly tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showing that IL-1β upregulates functional NK1R via NF-κB in astrocytes extended the NF-κB–dependent transcriptional regulation of NK1R to the CNS and implied a neuroinflammatory amplification loop.\",\n      \"evidence\": \"NF-κB reporter assay, CAPE inhibition, and Ca2+ mobilization in human astroglioma and rat primary astrocytes\",\n      \"pmids\": [\"15390113\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct NF-κB binding to the TACR1 promoter not demonstrated by ChIP\", \"Whether this mechanism operates in neurons in addition to glia was not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"NK1R−/− mice revealed that NK1R tonically maintains noradrenergic homeostasis by supporting somatodendritic α2a-autoreceptor function in the locus coeruleus, resolving how substance P modulates noradrenaline efflux in the frontal cortex.\",\n      \"evidence\": \"In vivo microdialysis, [35S]GTPγS binding in locus coeruleus, Western blot for noradrenaline transporter in NK1R−/− vs. WT mice\",\n      \"pmids\": [\"17331215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NK1R acts directly on LC neurons or indirectly through interneurons was not resolved\", \"Mechanism linking NK1R to α2a-adrenoceptor G-protein coupling is unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that monocytes express only the truncated NK1R isoform (NK1R-T), which cannot mobilize calcium alone but selectively activates ERK2 and cross-talks with CCR5, established isoform-specific signaling as a key feature of NK1R biology.\",\n      \"evidence\": \"NK1R-F transfection rescue, Ca2+ mobilization, chemotaxis, ERK1/2 and CCR5 phosphorylation assays with aprepitant in human monocytes\",\n      \"pmids\": [\"18835883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for differential G-protein/ERK coupling by truncated vs. full-length isoform not determined\", \"Whether NK1R-T/CCR5 crosstalk occurs in other immune cell types is unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"In vivo microdialysis in NK1R−/− mice demonstrated that NK1R is required for tonic dopamine efflux in the prefrontal cortex and for amphetamine-evoked striatal dopamine release, linking the receptor to mesolimbic/mesocortical dopaminergic function.\",\n      \"evidence\": \"Microdialysis in NK1R−/− mice and L-760735-treated wild-types with d-amphetamine challenge\",\n      \"pmids\": [\"19204064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NK1R acts on dopaminergic cell bodies (VTA) or terminals was not distinguished\", \"Downstream signaling cascade in dopamine neurons not characterized\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Spinal microglial activation was shown to be required for stress-induced NK1R upregulation and visceral hyperalgesia, positioning NK1R as both a downstream effector and an amplifier of central sensitization.\",\n      \"evidence\": \"Minocycline and p38 MAPK inhibitor intrathecal administration with visceromotor response measurement in stressed rats\",\n      \"pmids\": [\"19249394\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the microglia-derived factor that upregulates NK1R transcription is unknown\", \"Whether spinal NK1R upregulation is necessary or merely correlative for hyperalgesia was not dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"NK1R−/− mice showed reduced alcohol consumption and conditioned place preference in a gene-dose-dependent manner, and antagonist efficacy was abolished in KO mice, establishing NK1R as a necessary component of the alcohol reward circuit.\",\n      \"evidence\": \"Two-bottle choice, conditioned place preference, deprivation-escalation model with NK1R antagonist L-703,606 in NK1R KO and WT mice\",\n      \"pmids\": [\"20112009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Brain region(s) mediating NK1R's role in alcohol reward not identified in this study\", \"Downstream signaling linking NK1R to reward circuits not characterized\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A functional Tacr1 promoter SNP (−1372G/C) was shown to alter GATA-2/E2F-1 binding, elevate NK1R expression in the prefrontal cortex and amygdala, and confer sensitivity to NK1R antagonist-mediated suppression of alcohol self-administration, pinpointing the central amygdala as a critical locus.\",\n      \"evidence\": \"EMSA, luciferase reporter, radioligand binding, and intra-amygdala antagonist infusion in alcohol-preferring P-rats\",\n      \"pmids\": [\"23419547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the human TACR1 promoter carries analogous functional variants was not established\", \"Downstream amygdala circuit mechanisms not mapped\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Correlating NK1R isoform expression with SP internalization and targeted cytotoxicity in glioblastoma lines established that full-length NK1R—but not the truncated isoform—supports productive receptor internalization, a prerequisite for targeted therapeutic strategies.\",\n      \"evidence\": \"Radiolabeled and fluorescent SP binding/internalization, saporin-SP cytotoxicity across glioblastoma cell lines differing in NK1R-F/T ratios\",\n      \"pmids\": [\"24552486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not use genetic manipulation to confirm isoform causality\", \"Internalization trafficking route (clathrin vs. caveolae) not determined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"A neuron–tumor signaling loop was defined in which MMP1/PAR1-activated DRG neurons release substance P to activate NK1R/ERK on pancreatic cancer cells, promoting perineural invasion—extending NK1R's role to a direct pro-metastatic mechanism.\",\n      \"evidence\": \"Matrigel/DRG co-culture PNI system, sciatic nerve invasion model, MMP1 shRNA, NK1R antagonist, ERK pathway analysis\",\n      \"pmids\": [\"29896303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NK1R-T vs. NK1R-F isoform mediates perineural invasion signaling was not addressed\", \"Relevance to other perineural invasion–prone cancers not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Chemogenetic dissection of a Tacr1-expressing spinoparabrachial circuit revealed that spinal NK1R+ neurons drive sustained (but not acute) pain behaviors, while parabrachial NK1R+ neurons gate the behavioral response to prolonged noxious stimuli and suppress itch.\",\n      \"evidence\": \"DREADDs activation/silencing, circuit tracing, calcium imaging in spinal and PBN-SL Tacr1+ neurons in mice\",\n      \"pmids\": [\"33591273\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NK1R signaling itself (vs. merely marking the neurons) is required for circuit function is not resolved\", \"Synaptic mechanism by which PBN-SL Tacr1 neurons suppress itch is unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"NK1R antagonism after intracerebral hemorrhage shifted microglia to M2 polarization via suppression of PKC/p38MAPK/NF-κB, establishing a thrombin→SP→NK1R→PKC/NF-κB signaling cascade that drives neuroinflammation in hemorrhagic stroke.\",\n      \"evidence\": \"Intracerebroventricular agonist/antagonist, PKC agonist rescue, thrombin injection in a mouse ICH model\",\n      \"pmids\": [\"34244927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; no genetic confirmation of NK1R specificity\", \"Whether microglia express NK1R directly or respond indirectly was not confirmed by conditional KO\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A further downstream branch—NK1R/PKCδ/NLRC4 inflammasome—was shown to mediate neuronal pyroptosis after ICH, extending the neuropathological cascade from NF-κB-driven inflammation to GSDMD-dependent cell death.\",\n      \"evidence\": \"NLRC4 siRNA, PKCδ agonist rescue, aprepitant treatment in mouse ICH model\",\n      \"pmids\": [\"35922848\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; PKCδ–NLRC4 link not confirmed by independent genetic approaches\", \"Relative contribution of neuronal pyroptosis vs. microglial inflammation to outcome unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Tacr1-expressing ON cells in the RVM were identified as a descending anti-pruritic circuit that is potentiated by substance P, revealing a brainstem mechanism by which NK1R modulates itch-pain balance.\",\n      \"evidence\": \"Optotagging electrophysiology, intramedullary SP, chemogenetic activation of RVM Tacr1+ neurons, scratching behavior in mice\",\n      \"pmids\": [\"35972457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous substance P release in RVM is required for tonic itch suppression not tested\", \"Downstream spinal targets of RVM Tacr1 ON-cell projections not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for differential signaling by full-length vs. truncated NK1R isoforms, the identity of transcription factors directly binding the human TACR1 promoter NF-κB response elements, and whether NK1R signaling (rather than NK1R as a cell marker) is mechanistically required within the spinoparabrachial and RVM circuits.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of NK1R–SP complex in context of isoform-specific signaling\", \"Direct ChIP evidence for NF-κB at the TACR1 promoter is lacking\", \"Conditional NK1R knockout in defined circuits has not been performed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 9, 10, 11, 13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 13, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 11, 12, 14, 15]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 4, 9, 10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CCR5\",\n      \"TAC1\",\n      \"NLRC4\",\n      \"PRKCD\",\n      \"GATA2\",\n      \"E2F1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"TACR1 (NK-1R) is a Gq-coupled seven-transmembrane receptor for substance P and related tachykinins that transduces nociceptive, emetic, affective, and neuroinflammatory signals across central and peripheral tissues. The receptor binds peptide agonists via its N-terminal domain and first/second extracellular loops, while non-peptide antagonists occupy a distinct transmembrane pocket centered on His197 in TM5; after agonist stimulation it activates phospholipase C/PKC signaling from lipid-raft microdomains at the plasma membrane and, following clathrin/dynamin/β-arrestin–dependent endocytosis, sustains cytosolic PKC and nuclear ERK activation from endosomes to drive prolonged nociceptive excitation [PMID:1657150, PMID:8384323, PMID:15590676, PMID:28566424]. Alternative splicing produces a full-length isoform that predominates in the brain and supports high-affinity binding, Ca²⁺ mobilization, and receptor internalization, and a truncated isoform lacking 96 C-terminal residues that predominates in peripheral tissues and monocytes and signals through ERK2 and CCR5 crosstalk rather than canonical Ca²⁺ pathways [PMID:1310144, PMID:18835883, PMID:12752772]. Genetic ablation or pharmacological blockade of NK1R abolishes central sensitization and wind-up in spinal pain circuits, suppresses emesis, reduces alcohol reward, and produces antidepressant-like effects by elevating prefrontal noradrenergic and dopaminergic tone, while defined Tacr1-expressing spinoparabrachial and RVM circuits selectively mediate sustained pain and suppress itch [PMID:9537323, PMID:9733503, PMID:19204064, PMID:33591273, PMID:35972457].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Molecular cloning of TACR1 established it as a Gq/PLC-coupled GPCR that binds substance P with sub-nanomolar affinity and triggers IP3 production, resolving the molecular identity of the pharmacologically defined NK-1 receptor.\",\n      \"evidence\": \"cDNA cloning and heterologous expression in COS-7 cells with radioligand binding and IP3 assays, independently in two laboratories\",\n      \"pmids\": [\"1657150\", \"1718267\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling beyond IP3 not characterized\", \"No structural information on ligand-receptor interaction\", \"Receptor trafficking after activation unknown\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Identification of two alternatively spliced isoforms (full-length and truncated) and systematic mutagenesis of extracellular domains defined the structural basis for peptide agonist binding and revealed that the C-terminal tail is required for high-affinity coupling and full signaling efficacy.\",\n      \"evidence\": \"Gene structure determination (5 exons), chimeric receptor/mutagenesis approaches, heterologous expression in COS cells and Xenopus oocytes with binding and electrophysiology\",\n      \"pmids\": [\"1310144\", \"1280161\", \"1281469\", \"1312928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of the truncated isoform unknown\", \"Antagonist binding site not yet mapped\", \"No in vivo isoform-specific data\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of His197 in TM5 as essential for non-peptide antagonist binding demonstrated that agonist and antagonist binding pockets are spatially distinct, opening a structural framework for drug design.\",\n      \"evidence\": \"Site-directed mutagenesis with structure-activity analysis of CP 96345 analogues\",\n      \"pmids\": [\"8384323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No three-dimensional structure available\", \"Whether other TM residues contribute to the antagonist pocket not fully mapped\", \"Mechanism of antagonist-induced conformational change unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"NK1R knockout mice and a placebo-controlled clinical trial of MK-869 established that NK1R mediates central sensitization (wind-up) in pain and participates in mood regulation through a monoamine-independent mechanism, broadening the receptor's role beyond nociception.\",\n      \"evidence\": \"Targeted gene knockout with behavioral and electrophysiological phenotyping; randomized placebo-controlled clinical trial for depression; preclinical vocalization assays\",\n      \"pmids\": [\"9537323\", \"9733503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Monoamine-independent mechanism of antidepressant action not molecularly defined\", \"Whether NK1R signaling in mood uses the same PLC/PKC cascade as in pain unknown\", \"Circuit-level locus of NK1R's antidepressant action not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapping of isoform-specific expression in human brain (full-length dominant in locus coeruleus, ventral striatum) and identification of endokinins A/B as additional high-affinity endogenous agonists expanded the ligand-receptor framework and linked regional isoform distribution to mood and stress functions.\",\n      \"evidence\": \"TaqMan PCR and in situ hybridization in human brain; radioligand competition binding and hemodynamic assays for endokinins\",\n      \"pmids\": [\"12752772\", \"12716968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endokinins and SP activate distinct downstream pathways via NK1R unknown\", \"Isoform-specific signaling in native brain tissue not demonstrated\", \"NK1R role in emesis (brainstem) characterized pharmacologically but not genetically\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstration that NK1R resides in lipid rafts/caveolae and that raft integrity is required for PKC translocation, together with identification of SNX1/GASP as C-terminal tail interactors directing post-endocytic lysosomal sorting, defined the membrane-microdomain and trafficking framework for NK1R signaling.\",\n      \"evidence\": \"Sucrose gradient fractionation, cholesterol depletion/rescue, PKC translocation assays; systematic GST pull-down and SPR kinetics for C-tail interactors\",\n      \"pmids\": [\"15590676\", \"15452121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether raft localization is required in neurons (not just HEK293/HepG2) unknown\", \"Relative contribution of SNX1 vs GASP to degradation vs recycling not resolved\", \"Relationship between raft-dependent signaling and endosomal signaling not established\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"NK1R knockout mice revealed that tonic NK1R signaling maintains noradrenergic and dopaminergic tone by sustaining α2a-autoreceptor sensitivity in locus coeruleus and dopamine efflux in prefrontal cortex, providing a mechanistic basis for the antidepressant and ADHD-like phenotypes of NK1R loss.\",\n      \"evidence\": \"In vivo microdialysis for noradrenaline and dopamine in freely moving NK1R−/− mice; [³⁵S]GTPγS autoradiography for α2a coupling; psychostimulant challenge\",\n      \"pmids\": [\"17331215\", \"19204064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct synaptic mechanism by which NK1R regulates α2a-autoreceptor sensitivity not defined\", \"Whether dopaminergic and noradrenergic phenotypes share a common upstream mechanism unknown\", \"Translation to human neurochemistry not demonstrated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that monocytes express exclusively the truncated NK1R isoform, which signals through ERK2 and CCR5 crosstalk rather than Ca²⁺ mobilization, established isoform-specific signaling as a general principle with immunological relevance.\",\n      \"evidence\": \"Flow cytometry, RT-PCR, Ca²⁺ imaging, chemotaxis, and ERK1/2 phosphorylation in human monocytes; rescue by full-length transfection\",\n      \"pmids\": [\"18835883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for truncated isoform's selective ERK2 activation unknown\", \"Whether CCR5 and NK1R-T physically heterodimerize not determined\", \"In vivo immune consequences of isoform-specific signaling not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstration that NK1R signals from endosomes (not only the plasma membrane) to produce sustained PKC/ERK activation and prolonged pain established endosomal signaling as the pharmacologically relevant compartment and inspired endosome-targeted antagonist design.\",\n      \"evidence\": \"Pharmacological/genetic disruption of clathrin, dynamin, β-arrestin in spinal cord slices and in vivo pain models; cholestanol-conjugated antagonists targeting endosomal membranes\",\n      \"pmids\": [\"28566424\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endosomal signaling also underlies NK1R's roles in emesis and mood not tested\", \"Endosomal signaling pathway components beyond PKC/ERK not characterized\", \"Truncated isoform's endosomal signaling capacity unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Circuit-level studies using Tacr1-Cre genetics identified a spinoparabrachial Tacr1+ projection essential for sustained (but not acute) pain and RVM Tacr1+ ON cells that suppress itch, dissociating NK1R-defined circuits for pain and itch modulation.\",\n      \"evidence\": \"Chemogenetics, optogenetics, optotagging in Tacr1-Cre mice; behavioral nociception and itch assays\",\n      \"pmids\": [\"33591273\", \"35972457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signaling within Tacr1+ parabrachial neurons not characterized\", \"Whether the same or different SP sources drive the pain and itch circuits unknown\", \"Human translational evidence for these circuits lacking\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"NK1R was placed upstream of PKCδ→NLRC4 inflammasome-driven neuronal pyroptosis after intracerebral hemorrhage, extending its neuroinflammatory role to a defined cell-death pathway.\",\n      \"evidence\": \"Mouse ICH model with aprepitant, NK1R agonist reversal, PKCδ agonist reversal, NLRC4 siRNA epistasis; Western blot for pyroptosis markers\",\n      \"pmids\": [\"34244927\", \"35922848\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab findings not independently replicated\", \"Whether this pyroptosis pathway operates in non-hemorrhagic neuroinflammation unknown\", \"Direct physical interaction between NK1R signaling components and NLRC4 not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the structural basis for isoform-specific signaling, the contribution of endosomal versus plasma membrane signaling to non-nociceptive NK1R functions (mood, emesis, immune), and whether endokinin versus substance P agonism activates distinct downstream programs.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of agonist-bound full-length NK1R in a lipid bilayer\", \"Endosomal signaling paradigm untested outside pain\", \"Isoform-selective pharmacology not developed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [16, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 13]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [14, 26]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 13, 17, 26]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [7, 8, 19, 28, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 29, 30]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [7, 28]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SNX1\",\n      \"GASP1\",\n      \"NSF\",\n      \"ARRB1\",\n      \"CCR5\",\n      \"TAC1\",\n      \"TAC4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}