{"gene":"NMBR","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":1991,"finding":"NMBR (NMB-R) was cloned from human small cell lung carcinoma cells and shown to be pharmacologically distinct from the GRP receptor, with preferential high affinity for neuromedin B over GRP; expressed in Xenopus oocytes, a GRP-R-specific antagonist blocked GRP-R responses but not NMB-R responses, demonstrating distinct pharmacology.","method":"cDNA cloning, Xenopus oocyte expression, receptor binding, pharmacological antagonist blocking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted receptor in oocytes with functional pharmacological validation","pmids":["1655761"],"is_preprint":false},{"year":1993,"finding":"NMBR signals through a pertussis toxin-insensitive G protein coupled to phospholipase C, generating inositol trisphosphate and releasing intracellular calcium; agonist binding does not increase cAMP levels, establishing PLCβ/IP3/Ca2+ as the primary signaling pathway.","method":"Stable transfection in Balb/3T3 fibroblasts, [3H]inositol phosphate assay, intracellular calcium measurement, cAMP assay","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical assays in transfected cells with multiple orthogonal readouts","pmids":["7838118"],"is_preprint":false},{"year":1993,"finding":"Isoleucine-216 in transmembrane domain V (TM-V) of NMBR is critical for high-affinity NMB binding; the Ile216→Ser substitution abolished high-affinity NMB binding and severely impaired NMB-dependent inositol phosphate formation, while three other TM-V mutations did not affect binding.","method":"Site-directed mutagenesis of NMB-R/GRP-R chimeras, stable expression in Balb/3T3 fibroblasts, radioligand displacement assay, inositol phosphate assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with functional validation, multiple mutants tested","pmids":["8392057"],"is_preprint":false},{"year":1993,"finding":"Distinct NMBR and GRP-R subtypes are expressed on human and rabbit colonic smooth muscle cells; antisense oligonucleotides selectively blocking NMBR mRNA translation inhibited neuromedin B-induced contraction without affecting GRP-induced contraction, demonstrating receptor-subtype-specific contractile roles.","method":"RT-PCR for receptor mRNA, antisense oligonucleotide-mediated mRNA knockdown, smooth muscle contraction assay","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — selective antisense knockdown with specific functional readout","pmids":["8253343"],"is_preprint":false},{"year":1994,"finding":"NMBR undergoes rapid homologous desensitization following agonist stimulation via receptor down-regulation mediated by internalization; recovery (resensitization) of surface NMB-R is independent of new protein synthesis and is due to recycling from an intracellular compartment, as shown by monensin (recycling inhibitor) blocking recovery but cycloheximide not affecting it.","method":"Radioligand binding assay on native C-6 glioblastoma cells and stably transfected Balb/3T3 cells, inositol phosphate/Ca2+ assays, monensin and cycloheximide treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, native and transfected cell systems, pharmacological dissection of recycling vs. synthesis","pmids":["8163469"],"is_preprint":false},{"year":1998,"finding":"Four specific amino acid residues conserved in NMBR and GRP-R (but diverged in BRS-3) are critical for high-affinity NMB binding to NMBR; substituting these four residues into BRS-3 (4ΔBRS-3) increased NMB affinity to near wild-type NMBR levels, while these substitutions did not create high affinity for the non-peptide antagonist PD168368, indicating distinct structural determinants for peptide vs. non-peptide binding.","method":"Site-directed mutagenesis of BRS-3, radioligand binding assay, comparison across receptor subtypes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with rigorous binding validation across multiple receptor constructs","pmids":["9632639"],"is_preprint":false},{"year":1999,"finding":"PD168368 is a potent, competitive, and selective antagonist at NMBR across human, mouse, rat, and frog species (Ki = 15–45 nM), with 30–60-fold lower affinity for GRP-R and >300-fold lower affinity for BRS-3; it inhibits NMB-induced Ca2+ and inositol phosphate responses without acting as an agonist.","method":"Radioligand binding competition assay, intracellular calcium and [3H]inositol phosphate assays across multiple species receptor variants","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 2 — multi-species, multi-cell pharmacological characterization with orthogonal functional assays","pmids":["10454496"],"is_preprint":false},{"year":2000,"finding":"Rational design of BRS-3-selective agonists using conformationally restricted amino acid substitutions (specifically (R)- or (S)-amino-3-phenylpropionic acid at position 11) into the prototype bombesin analog confirmed that NMBR (and GRP-R) require distinct pharmacophore features from BRS-3 for selective high-affinity binding; BRS-3 selective agonists functioned via phospholipase C/inositol phosphate pathway.","method":"Rational peptide design, radioligand binding, [3H]inositol phosphate assay, molecular modeling","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1-2 — structure-activity study with functional validation, but primarily focused on BRS-3 selectivity","pmids":["11112777"],"is_preprint":false},{"year":2002,"finding":"NMBR-deficient female mice show impaired recovery of maternal behavior after restraint stress compared to wild-type mice, demonstrating that the NMB/NMBR pathway modulates stress resilience and maternal behavior in vivo.","method":"Nmbr knockout mice, maternal behavior scoring before and after restraint stress","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined behavioral phenotype, but no downstream molecular mechanism identified","pmids":["12231437"],"is_preprint":false},{"year":2002,"finding":"NMB-R-deficient female mice exhibit decreased marble burying behavior associated with elevated 5-HT immunostaining in the dorsal raphe nucleus and downregulated 5-HT1A receptor gene expression, suggesting NMB/NMBR modulates dorsal raphe serotonergic neuron activity; 5-HT depletion with p-CPA reversed the burying deficit in KO mice.","method":"Nmbr knockout mice, marble burying behavioral test, HPLC for brain 5-HT levels, immunohistochemistry, quantitative RT-PCR, p-CPA pharmacological depletion","journal":"Brain research","confidence":"Medium","confidence_rationale":"Tier 2 — KO with multiple biological readouts and pharmacological rescue, replicated in same KO line","pmids":["12031854"],"is_preprint":false},{"year":2004,"finding":"NMBR is expressed in normal and cancerous human colonic epithelial cells and functions as a mitogen; exogenous NMB was 50–100% more efficacious than GRP in stimulating proliferation of colon cancer cell lines (Caco-2, HT-29) and also promoted proliferation of non-malignant NCM-460 colonic epithelial cells, acting in an autocrine fashion.","method":"Immunohistochemistry, Western blot with deglycosylation, cell proliferation assays in multiple colonic cell lines","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cell lines with direct proliferation assays, protein characterization","pmids":["15528253"],"is_preprint":false},{"year":2006,"finding":"Bombesin receptor BB1 (NMBR) antagonist PD176252, administered to the dorsal raphe nucleus (DRN), increased social interaction and suppressed NMB-stimulated in vivo 5-HT release in the ventral hippocampus; intra-DRN NMB agonist (NMB-30) promoted 5-HT release and suppressed social interaction, an effect blocked by a 5-HT2C (but not 5-HT1A) receptor antagonist, establishing that NMBR at the DRN drives 5-HT release to the ventral hippocampus mediating anxiogenesis.","method":"Intra-DRN microinfusion, in vivo microdialysis for hippocampal 5-HT, social interaction test, fear-potentiated startle, pharmacological receptor antagonists","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — in vivo microdialysis with site-specific microinfusion and multiple behavioral/neurochemical readouts","pmids":["17035523"],"is_preprint":false},{"year":2011,"finding":"The NMBR antagonist PD168368 inhibited NMB-induced angiogenesis both in vitro and in vivo, induced cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells, and suppressed tumor growth in a xenograft model, demonstrating that NMBR signaling promotes tumor angiogenesis and cancer cell survival.","method":"In vitro angiogenesis assay, in vivo Matrigel plug angiogenesis, xenograft tumor model, cell cycle and apoptosis analysis","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro and in vivo assays with selective receptor antagonist","pmids":["21908103"],"is_preprint":false},{"year":2014,"finding":"NMBR and GRPR exhibit cross-inhibitory signaling in the spinal cord to maintain normal histaminergic itch transmission: Nmbr KO mice show enhanced GRPR activity (and vice versa) without upregulation of receptor expression; double KO (Nmbr/Grpr) mice show significant deficits in histamine-evoked scratching but not chloroquine-evoked scratching, indicating GRPR alone mediates non-histaminergic itch while the two receptors compensate for each other in histaminergic itch. GRPR+ neurons act downstream of NMBR+ neurons in integrating NMB-NMBR-encoded histaminergic itch.","method":"Single and double knockout mice, intradermal pruritogen injection, scratching behavior quantification, receptor expression analysis","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double KO, multiple pruritogens, replicated behavioral readouts","pmids":["25209280"],"is_preprint":false},{"year":2017,"finding":"Chicken NMBR (cNMBR) expressed in CHO cells is potently and specifically activated by cNMB (not cGRP), as monitored by luciferase reporter assays, confirming conservation of ligand selectivity across vertebrates; cNMBR is mainly expressed in the brain and testes.","method":"CHO cell expression, cell-based luciferase reporter assay, qPCR tissue expression profiling","journal":"Journal of molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — functional receptor characterization in heterologous expression system","pmids":["28500250"],"is_preprint":false},{"year":2020,"finding":"Homology modeling of NMBR followed by docking of peptoid antagonists PD168368 and PD176252 defined a pharmacophore for BB1 receptor binding; in silico screening identified structurally diverse small molecules with selective affinity for NMBR but not GRP-R (BB2), providing initial structural insight into NMBR ligand binding.","method":"Homology modeling, molecular docking, pharmacophore-based virtual screening, radioligand binding validation","journal":"Pharmaceuticals (Basel, Switzerland)","confidence":"Low","confidence_rationale":"Tier 4 — primarily computational with limited experimental validation","pmids":["32824403"],"is_preprint":false},{"year":2021,"finding":"BNP facilitates NMB-encoded histaminergic itch through a novel NPRC-NMBR cross-signaling mechanism: NPRC (encoded by Npr3) partially co-localizes with NMBR in spinal cord laminae I-II; NPRC is required for histamine- but not chloroquine-evoked itch; BNP significantly facilitates NMB-mediated (but not GRP-mediated) scratching; BNP evoked Ca2+ responses in NMBR/NPRC HEK293 cells and dorsal horn neurons co-expressing both receptors, revealing a Gi-coupled NPRC potentiating Gq-coupled NMBR signaling.","method":"Npr3 knockout mice, behavioral itch assays, Ca2+ imaging in HEK293 cells co-expressing NMBR and NPRC, dorsal horn neuron recordings","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, heterologous co-expression Ca2+ imaging, and behavioral pharmacology providing convergent evidence","pmids":["34919054"],"is_preprint":false},{"year":2023,"finding":"Steered molecular dynamics modeling of bombesin bound to NMBR and GRP-R identified receptor residues important for high affinity binding and explained differential binding affinity between the two receptors; models revealed distinct bound conformations of bombesin at BB1R vs. BB2R consistent with mutagenesis data.","method":"Steered molecular dynamics simulation, homology modeling, structure-activity analysis","journal":"International journal of biological macromolecules","confidence":"Low","confidence_rationale":"Tier 4 — computational only, no new experimental validation","pmids":["37956803"],"is_preprint":false},{"year":2009,"finding":"NMBR mRNA and protein expression peaks at the onset of labor in mouse myometrium; NF-κB p65 DNA-binding activity positively correlates with NMBR mRNA expression, and NMBR expression correlates with IL-6 and HSP70 expression, suggesting NMBR participates in parturition via NF-κB p65–IL-6 signaling and may influence onset of labor by regulating HSP70 through a p65-independent pathway.","method":"Semi-quantitative RT-PCR, Western blot, NF-κB p65 DNA-binding activity assay (NoShift kit) across pregnancy stages","journal":"Zhong nan da xue xue bao. Yi xue ban","confidence":"Low","confidence_rationale":"Tier 3 — correlational evidence between receptor expression and signaling molecules, no direct mechanistic manipulation","pmids":["19587437"],"is_preprint":false},{"year":2025,"finding":"NMB/NMBR signaling restricts H9N2 influenza virus replication by potentiating IFN-β production; mechanistically, NMBR activation upregulates TRIM25 (an E3 ubiquitin ligase) to target viral NS1 protein, and engages a positive feedback loop with the RIG-I pathway by enhancing K63-linked ubiquitination of RIG-I while transcriptionally repressing the deubiquitinase CYLD, resulting in augmented JAK-STAT1 signaling and increased ISG15 expression.","method":"NMB treatment and NMBR overexpression/knockdown in A549 cells and mouse lungs, viral replication assays, IFN-β ELISA, TRIM25 and CYLD expression analysis, ubiquitination assays, STAT1 phosphorylation","journal":"Veterinary microbiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple mechanistic steps validated with gain- and loss-of-function in cell and animal models","pmids":["41242095"],"is_preprint":false},{"year":2025,"finding":"NMB binding to NMBR in goat granulosa cells activates PLCβ1, triggering ER Ca2+ release and raising cytosolic Ca2+ while alleviating ER stress; NMBR signaling strengthens mitochondria-associated ER membrane (MAM) formation via the IRE1α–IP3R–VDAC1 axis, facilitating Ca2+ transfer into mitochondria, enhancing mitochondrial membrane potential, respiratory chain complex activities, and ATP production, thereby promoting granulosa cell proliferation. An NMBR antagonist abolished these effects.","method":"Exogenous NMB treatment, NMBR antagonist, Ca2+ imaging, cell cycle analysis (S-phase fraction), CCNE1/CDK expression, mitochondrial membrane potential, ATP assay, MAM formation analysis","journal":"Journal of ovarian research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal mechanistic readouts with pharmacological validation using NMBR antagonist","pmids":["41257985"],"is_preprint":false},{"year":2025,"finding":"Bombesin stimulates dorsal raphe nucleus serotonergic neurons in vivo via a mechanism involving NMBR (BB1 receptor); intravenous Tat-bombesin increased 5-HT neuron firing activity, and the NMBR antagonist PD176252 had the opposite effect, confirming that GRP/bombesin regulates 5-HT neurotransmission through BB1 receptors.","method":"In vivo single-unit electrophysiology of dorsal raphe 5-HT neurons, Tat-bombesin administration, PD176252 antagonist","journal":"General physiology and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo electrophysiology with pharmacological antagonism, consistent with prior microdialysis evidence","pmids":["40114617"],"is_preprint":false},{"year":2026,"finding":"Bombesin ameliorates visceral hypersensitivity and colonic hyperpermeability in LPS- and CRF-induced IBS rat models via BB1 (NMBR) receptor-dependent mechanisms; effects were abolished by BB1 antagonism and reproduced by BB1 receptor activation but not BB2 activation. Mechanistic pathways involve AMPK, GABAA, nitric oxide, opioid, peripheral CRF receptor subtype 2, neurotensin receptor 1, and central orexin/dopamine D2/muscarinic receptor signaling, and suppression of IL-1β and preservation of occludin expression.","method":"IBS rat models (LPS and CRF), EMG recording of visceral pain, colonic permeability (Evans blue), occludin immunoblot, IL-1β ELISA, selective BB1/BB2 agonists and antagonists","journal":"European journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vivo models with receptor-selective pharmacology and mechanistic pathway dissection","pmids":["41548687"],"is_preprint":false},{"year":2024,"finding":"Photostimulation of parafacial NMB neurons or preBötzinger Complex (preBötC) NMBR neurons elicits ectopic sighs; however, ectopic sighs can also be produced without involvement of NMB peptide or NMBR (via preBötC SST neuron activation even in the presence of NMBR and GRPR antagonists), indicating NMBR-expressing neurons participate in but are not exclusively required for sigh generation, and that preBötC SST neurons are downstream elements converting normal breaths to sighs.","method":"Optogenetic photostimulation of NMB/NMBR neurons, chemogenetic and optogenetic activation of preBötC SST neurons, NMBR/GRPR antagonist pharmacology in vivo","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — circuit-level optogenetic and chemogenetic dissection in vivo","pmids":[],"is_preprint":true}],"current_model":"NMBR is a Gq-coupled seven-transmembrane G protein-coupled receptor that binds neuromedin B with high affinity (determined critically by Ile216 in TM-V and four conserved residues shared with GRP-R), activates PLCβ/IP3/Ca2+ signaling (without cAMP elevation), undergoes agonist-induced homologous desensitization via internalization and recycling, and mediates diverse physiological functions including spinal cord itch transmission (cross-inhibiting with GRPR via an NPRC co-receptor mechanism), anxiogenesis through dorsal raphe 5-HT release, sigh generation in the preBötzinger Complex, granulosa cell proliferation via MAM-mediated mitochondrial Ca2+ transfer, antiviral innate immunity through RIG-I/TRIM25/JAK-STAT1 potentiation, and gut-brain axis regulation of visceral sensitivity."},"narrative":{"teleology":[{"year":1991,"claim":"Molecular cloning of NMBR from human SCLC cells established it as a receptor pharmacologically distinct from GRP-R, resolving the question of whether bombesin-family peptides acted through a single receptor or multiple subtypes.","evidence":"cDNA cloning, Xenopus oocyte expression with radioligand binding and subtype-selective antagonist blockade","pmids":["1655761"],"confidence":"High","gaps":["No structural information for the receptor","Downstream signaling pathway not yet defined"]},{"year":1993,"claim":"Identification of PLC/IP3/Ca²⁺ as the primary NMBR signaling cascade (with no cAMP involvement) and of Ile216 in TM-V as a critical determinant of NMB binding selectivity established both the signaling mechanism and structural basis of ligand discrimination.","evidence":"Stable transfection in Balb/3T3 fibroblasts with inositol phosphate, Ca²⁺, and cAMP assays; site-directed mutagenesis of NMB-R/GRP-R chimeras with radioligand binding","pmids":["7838118","8392057"],"confidence":"High","gaps":["G protein identity (Gq vs. G11) not directly determined","Role of other TM domains in ligand binding uncharacterized"]},{"year":1994,"claim":"Demonstration that NMBR undergoes rapid agonist-induced internalization followed by recycling-dependent resensitization (independent of new protein synthesis) established the receptor's desensitization mechanism.","evidence":"Radioligand binding in C-6 glioblastoma and Balb/3T3 cells with monensin (recycling inhibitor) and cycloheximide treatment","pmids":["8163469"],"confidence":"High","gaps":["Kinases mediating receptor phosphorylation/internalization not identified","β-arrestin involvement not tested"]},{"year":1998,"claim":"Transfer of four conserved NMBR/GRP-R residues into BRS-3 conferred near-wild-type NMB affinity, pinpointing the minimal structural determinants for peptide ligand recognition across the bombesin receptor family.","evidence":"Site-directed mutagenesis of BRS-3, radioligand binding across receptor constructs","pmids":["9632639"],"confidence":"High","gaps":["Determinants of non-peptide antagonist binding shown to differ but not fully mapped","No crystal or cryo-EM structure available"]},{"year":1999,"claim":"Characterization of PD168368 as a potent, selective NMBR antagonist across multiple species provided a critical pharmacological tool for dissecting NMBR function in vivo.","evidence":"Multi-species radioligand binding competition and functional Ca²⁺/IP3 assays","pmids":["10454496"],"confidence":"High","gaps":["In vivo selectivity and pharmacokinetics not fully profiled","No structural basis for antagonist selectivity"]},{"year":2002,"claim":"Nmbr-knockout mouse studies linked NMBR to serotonergic modulation in the dorsal raphe and stress-related behaviors, revealing its CNS role beyond peripheral peptide signaling.","evidence":"Nmbr KO mice with marble burying behavior, brain 5-HT immunohistochemistry, 5-HT1A qRT-PCR, and p-CPA rescue; separate KO study of maternal behavior after restraint stress","pmids":["12031854","12231437"],"confidence":"Medium","gaps":["Direct electrophysiological evidence of NMBR action on 5-HT neurons not yet shown","Molecular mechanism linking NMBR to 5-HT1A downregulation unclear"]},{"year":2006,"claim":"Site-specific microinfusion and microdialysis established that NMBR activation in the dorsal raphe nucleus directly drives serotonin release to the ventral hippocampus, mediating anxiogenic behavior through downstream 5-HT2C receptors.","evidence":"Intra-DRN microinfusion of NMB agonist and BB1 antagonist, in vivo microdialysis for hippocampal 5-HT, social interaction and fear-potentiated startle tests","pmids":["17035523"],"confidence":"High","gaps":["Whether NMBR acts directly on 5-HT neurons or via interneurons not resolved","Translational relevance to human anxiety not tested"]},{"year":2014,"claim":"Genetic epistasis using single and double Nmbr/Grpr knockout mice revealed that NMBR and GRPR cross-inhibit to maintain normal histaminergic itch, with GRPR+ neurons acting downstream of NMBR+ neurons, defining a spinal itch circuit hierarchy.","evidence":"Nmbr, Grpr, and double KO mice with intradermal pruritogen injection and scratching quantification","pmids":["25209280"],"confidence":"High","gaps":["Molecular mechanism of cross-inhibition not defined","Identity of interneurons connecting NMBR+ to GRPR+ neurons unknown"]},{"year":2021,"claim":"Discovery that NPRC co-localizes with NMBR in spinal cord laminae I–II and that BNP potentiates NMB/NMBR Ca²⁺ signaling through Gi-coupled NPRC revealed a novel cross-receptor mechanism facilitating histaminergic itch transmission.","evidence":"Npr3 KO mice, behavioral itch assays, Ca²⁺ imaging in HEK293 cells co-expressing NMBR/NPRC, dorsal horn neuron recordings","pmids":["34919054"],"confidence":"High","gaps":["Signaling intermediates linking Gi (NPRC) to Gq (NMBR) potentiation not identified","Whether this mechanism operates outside the spinal cord unknown"]},{"year":2025,"claim":"Multiple studies expanded NMBR's functional repertoire: antiviral innate immunity via RIG-I/TRIM25/JAK-STAT1 potentiation, granulosa cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer, dorsal raphe 5-HT neuron activation by in vivo electrophysiology, and visceral hypersensitivity regulation in IBS models through BB1-selective mechanisms.","evidence":"NMBR overexpression/knockdown in A549 cells and mouse lungs with viral replication and ubiquitination assays; NMB treatment of goat granulosa cells with Ca²⁺ imaging and MAM analysis; in vivo single-unit electrophysiology of dorsal raphe neurons; IBS rat models with BB1-selective pharmacology","pmids":["41242095","41257985","40114617","41548687"],"confidence":"Medium","gaps":["Antiviral role demonstrated only for H9N2 influenza; breadth across other viruses unknown","MAM mechanism shown in goat granulosa cells; conservation in human not confirmed","IBS model pharmacology involves many downstream pathways; direct NMBR effectors not fully delineated"]},{"year":null,"claim":"No experimental three-dimensional structure of NMBR has been determined; the molecular basis of Gq coupling, β-arrestin recruitment kinetics, and the precise circuit identities of NMBR-expressing neurons in itch and respiratory circuits remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure of NMBR","β-arrestin and GRK specificity not experimentally determined","Cell-type-specific transcriptomic identity of spinal NMBR+ neurons incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,6,14]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,4,16]}],"pathway":[],"complexes":[],"partners":["NMB","GRPR","NPR3","TRIM25","PLCΒ1"],"other_free_text":[]},"mechanistic_narrative":"NMBR (BB1 receptor) is a Gq-coupled G protein-coupled receptor that selectively binds neuromedin B with high affinity to activate phospholipase C/IP3/Ca²⁺ signaling, mediating diverse physiological processes including itch transmission, anxiety-related behavior, respiratory patterning, cellular proliferation, and visceral sensitivity. Cloned from human small cell lung carcinoma cells, NMBR is pharmacologically distinct from the related GRP receptor (BB2), with ligand selectivity critically determined by Ile216 in transmembrane domain V and four conserved residues shared with GRP-R [PMID:1655761, PMID:8392057, PMID:9632639]. In the spinal cord, NMBR mediates histaminergic itch through a cross-inhibitory relationship with GRPR, potentiated by a Gi-coupled NPRC co-receptor mechanism that facilitates NMB-encoded signaling [PMID:25209280, PMID:34919054]. In the dorsal raphe nucleus, NMBR activation drives serotonin release to the ventral hippocampus to promote anxiogenic behavior, while peripheral NMBR signaling promotes granulosa cell and colonic epithelial cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer and autocrine mitogenic pathways, respectively [PMID:17035523, PMID:41257985, PMID:15528253]."},"prefetch_data":{"uniprot":{"accession":"P28336","full_name":"Neuromedin-B receptor","aliases":["Epididymis tissue protein Li 185a","Neuromedin-B-preferring bombesin receptor"],"length_aa":390,"mass_kda":43.4,"function":"Receptor for neuromedin-B (PubMed:1655761). Contributes to the maintenance of basal sigh rate through signaling in the pre-Botzinger complex, a cluster of several thousand neurons in the ventrolateral medulla responsible for inspiration during respiratory activity (By similarity). Contributes to the induction of sneezing following exposure to chemical irritants or allergens which causes release of NMB by nasal sensory neurons and activation of NMBR-expressing neurons in the sneeze-evoking region of the brainstem (By similarity). These in turn activate neurons of the caudal ventral respiratory group, giving rise to the sneezing response (By similarity). Contributes to induction of acute itch, possibly through its activation on dorsal root ganglion neurons by the NMB peptide (By similarity). Plays a role in the innate immune response to influenza A virus infection by enhancing interferon alpha expression and reducing expression of IL6 (PubMed:31601264). Plays a role in CSF1-induced proliferation of osteoclast precursors by contributing to the positive regulation of the expression of the CSF1 receptor CSF1R (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P28336/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NMBR","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NMBR","total_profiled":1310},"omim":[{"mim_id":"305670","title":"GASTRIN-RELEASING PEPTIDE RECEPTOR; GRPR","url":"https://www.omim.org/entry/305670"},{"mim_id":"162341","title":"NEUROMEDIN B RECEPTOR; NMBR","url":"https://www.omim.org/entry/162341"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Not detected","tissue_distribution":"Not detected","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NMBR"},"hgnc":{"alias_symbol":["BB1","BB1R","BRS1"],"prev_symbol":[]},"alphafold":{"accession":"P28336","domains":[{"cath_id":"1.20.1070.10","chopping":"36-244_257-337","consensus_level":"high","plddt":92.6684,"start":36,"end":337}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P28336","model_url":"https://alphafold.ebi.ac.uk/files/AF-P28336-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P28336-F1-predicted_aligned_error_v6.png","plddt_mean":79.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NMBR","jax_strain_url":"https://www.jax.org/strain/search?query=NMBR"},"sequence":{"accession":"P28336","fasta_url":"https://rest.uniprot.org/uniprotkb/P28336.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P28336/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P28336"}},"corpus_meta":[{"pmid":"7681471","id":"PMC_7681471","title":"Activated T cells induce expression of B7/BB1 on normal or leukemic B cells through a CD40-dependent signal.","date":"1993","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/7681471","citation_count":541,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"7678111","id":"PMC_7678111","title":"Induction of alloantigen-specific hyporesponsiveness in human T lymphocytes by blocking interaction of CD28 with its natural ligand B7/BB1.","date":"1993","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/7678111","citation_count":501,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"1847724","id":"PMC_1847724","title":"The CD28 ligand B7/BB1 provides costimulatory signal for alloactivation of CD4+ T cells.","date":"1991","source":"The Journal of experimental 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After maximal down-regulation, receptor recovery at the cell surface is independent of protein synthesis and occurs via recycling from an intracellular site (blocked by monensin, not cycloheximide), with resensitization paralleling receptor reappearance.\",\n      \"method\": \"Radioligand binding assays, inositol phosphate assays, calcium measurements on native C-6 glioblastoma cells and NMB-R-transfected Balb/3T3 fibroblasts; monensin and cycloheximide pharmacological dissection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in transfected cells plus native cells, multiple orthogonal assays, pharmacological dissection of mechanism\",\n      \"pmids\": [\"8163469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NMBR and GRPR maintain normal histaminergic itch transmission through cross-inhibitory signaling: loss of NMBR alone does not impair scratching, but double knockout of both Nmbr and Grpr causes significant deficits in histamine-evoked itch. GRPR activity is enhanced in Nmbr KO mice and vice versa without receptor upregulation, indicating functional cross-compensation. NMB signals exclusively through NMBR, while GRP can signal through both receptors. GRPR+ neurons act downstream of NMBR+ neurons to integrate NMB-NMBR-encoded histaminergic itch.\",\n      \"method\": \"Genetic knockout mice (single and double KO), intradermal pruritogen injection behavioral assays, scratch behavior quantification, genetic epistasis analysis\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined behavioral phenotype, epistasis analysis, replicated across multiple pruritogen conditions\",\n      \"pmids\": [\"25209280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"BNP facilitates NMB-encoded histaminergic itch through a novel NPRC-NMBR cross-signaling mechanism. NPRC (encoded by Npr3) expression overlaps with NMBR in laminae I-II of the dorsal horn. BNP significantly facilitates scratching mediated by NMB but not GRP, and evokes Ca2+ responses in NMBR/NPRC co-expressing HEK293 cells and dorsal horn neurons, indicating that BNP acts via NPRC to potentiate Gq-coupled PLCβ-Ca2+ signaling through NMBR.\",\n      \"method\": \"Npr3 KO mice, intradermal pruritogen injection behavioral assays, Ca2+ imaging in HEK293 cells co-expressing NMBR and NPRC, immunostaining, genetic epistasis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with defined phenotype plus in vitro Ca2+ signaling reconstitution in co-expressing cells, multiple orthogonal methods\",\n      \"pmids\": [\"34919054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Bombesin BB1 receptor activity at the dorsal raphe nucleus (DRN) modulates serotonin (5-HT) release: intra-DRN microinfusion of NMB (BB1/BB2 agonist) promotes in vivo 5-HT release in the ventral hippocampus, while BB1/BB2 receptor antagonist PD 176252 suppresses it. The anxiogenic effect of intra-DRN NMB is attenuated by a 5-HT2C receptor antagonist, placing NMBR upstream of 5-HT2C signaling in anxiety circuits.\",\n      \"method\": \"In vivo microdialysis (5-HT measurement in ventral hippocampus), intra-DRN microinfusion, pharmacological receptor antagonism, multiple ethologically relevant anxiety behavioral tests\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo microdialysis with pharmacological dissection, multiple behavioral paradigms, intra-DRN site-specific infusions\",\n      \"pmids\": [\"17035523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Loss of NMBR in female mice impairs stress resilience in maternal behavior: NMB-R-deficient mice show normal maternal behavior under non-stressed conditions but fail to recover maternal behavior after restraint stress, indicating that the NMB/NMBR pathway is required for stress-induced recovery of maternal behavior.\",\n      \"method\": \"NMB-R knockout mice, restraint stress paradigm, maternal behavior scoring\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined behavioral phenotype, single lab, single behavioral paradigm\",\n      \"pmids\": [\"12231437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NMB-R deficiency in female mice leads to decreased marble burying behavior associated with elevated 5-HT expression in the dorsal raphe nucleus and downregulation of 5-HT1A receptor gene expression, suggesting NMBR modulates serotonergic activity by affecting dorsal raphe function.\",\n      \"method\": \"NMB-R knockout mice, marble burying behavioral test, 5-HT depletion with p-CPA, HPLC brain 5-HT measurement, immunohistochemistry, quantitative RT-PCR\",\n      \"journal\": \"Brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with behavioral phenotype plus neurochemical characterization, multiple methods in single lab\",\n      \"pmids\": [\"12031854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Chicken NMBR expressed in CHO cells is potently activated by chicken NMB but not GRP (as monitored by luciferase reporter assays), confirming NMBR as the NMB-specific receptor in birds, consistent with mammalian NMBR function.\",\n      \"method\": \"Heterologous expression in CHO cells, cell-based luciferase reporter assays, quantitative RT-PCR, Western blot, immunostaining\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution in heterologous cells confirming receptor-ligand specificity, ortholog confirmation\",\n      \"pmids\": [\"28500250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NMB/NMBR signaling restricts H9N2 influenza virus replication by upregulating TRIM25 (an E3 ubiquitin ligase) to target viral NS1 protein, and by activating a positive feedback loop with the RIG-I pathway through enhanced K63-linked ubiquitination of RIG-I and transcriptional repression of the deubiquitinase CYLD, leading to augmented JAK-STAT1 signaling and increased ISG15 expression.\",\n      \"method\": \"NMB treatment and NMBR overexpression/knockdown in A549 cells and mouse lungs, viral replication assays, IFN-β measurement, ubiquitination assays, Western blot for STAT1 phosphorylation, gene expression analysis\",\n      \"journal\": \"Veterinary microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with mechanistic pathway dissection, multiple signaling readouts, single lab\",\n      \"pmids\": [\"41242095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NMB binds NMBR to activate phospholipase C β1 (PLCβ1), triggering ER Ca2+ release, elevating cytosolic Ca2+ levels, and strengthening mitochondria-associated ER membranes (MAMs) via the IRE1α–IP3R–VDAC1 axis to facilitate Ca2+ transfer into mitochondria, thereby enhancing mitochondrial function and promoting granulosa cell proliferation. These effects are abolished by an NMBR antagonist.\",\n      \"method\": \"Exogenous NMB treatment of goat granulosa cells, NMBR antagonist blockade, Ca2+ imaging, flow cytometry cell cycle analysis, mitochondrial membrane potential measurement, respiratory chain complex activity assays, ATP measurement, Western blot\",\n      \"journal\": \"Journal of ovarian research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological activation/inhibition with multiple orthogonal cellular and biochemical readouts, single lab\",\n      \"pmids\": [\"41257985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NMBR expression in mouse myometrium peaks at parturition at both mRNA and protein levels, and NF-κB p65 DNA-binding activity positively correlates with NMBR mRNA expression, suggesting NMBR participates in parturition via a NF-κB p65–IL-6 signaling pathway.\",\n      \"method\": \"Semi-quantitative RT-PCR, Western blot, NF-κB p65 DNA-binding activity assay (NoShift transcription factor assay), in vivo mouse model across gestational stages\",\n      \"journal\": \"Zhong nan da xue xue bao\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — correlative evidence with no direct functional manipulation of NMBR, single lab\",\n      \"pmids\": [\"19587437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Photostimulation of preBötzinger Complex (preBötC) NMBR neurons elicits ectopic sighs, but sigh generation can also occur without involvement of NMB peptide or NMBR in preBötC. preBötC SST neurons act downstream and can generate sighs even in the presence of NMBR and/or GRPR antagonists, indicating NMBR neuron activation contributes to but is not exclusively required for sigh generation.\",\n      \"method\": \"Optogenetic photostimulation of NMBR neurons, chemogenetic activation, NMBR/GRPR antagonist pharmacology, in vivo mouse respiratory recording\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — optogenetic/chemogenetic activation with pharmacological dissection, clean circuit-level phenotype, preprint\",\n      \"pmids\": [\"bio_10.1101_2024.06.05.597565\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Bombesin ameliorates visceral hypersensitivity and colonic hyperpermeability in IBS rat models via BB1 (NMBR) receptor-dependent mechanisms, involving multiple gut-brain axis pathways including AMPK, GABAA, nitric oxide, opioid, peripheral CRF receptor subtype 2, neurotensin receptor 1, and central orexin, dopamine D2, and muscarinic receptors; bombesin also suppresses LPS-induced IL-1β and preserves occludin expression through BB1 receptor.\",\n      \"method\": \"Intraperitoneal bombesin administration in LPS- and CRF-induced rat IBS models, selective BB1/BB2 receptor agonists/antagonists, EMG recording of visceral pain, Evans blue colonic permeability assay, immunoblotting for occludin and ELISA for IL-1β\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — selective receptor pharmacology with multiple pathway antagonists and functional readouts, single lab\",\n      \"pmids\": [\"41548687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Bombesin stimulates dorsal raphe nucleus 5-HT neuron firing via a mechanism involving BB1 (NMBR) receptors: Tat-bombesin increased 5-HT neuron firing activity in vivo, and the BB1 receptor antagonist PD 176252 had the opposite effect.\",\n      \"method\": \"In vivo single-unit electrophysiology of dorsal raphe 5-HT neurons, BB1 receptor antagonist pharmacology\",\n      \"journal\": \"General physiology and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo electrophysiology with pharmacological receptor dissection, single lab\",\n      \"pmids\": [\"40114617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Molecular modeling and docking of BB1 (NMBR) receptor identified key stereochemical features of the binding site; small molecules identified through pharmacophore-based in silico screening showed affinity to BB1 but not BB2 receptor, revealing differential binding determinants between the two receptors.\",\n      \"method\": \"Homology modeling of NMBR 3D structure, molecular docking, pharmacophore-based virtual screening, binding affinity assays\",\n      \"journal\": \"Pharmaceuticals\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — primarily computational with limited experimental validation\",\n      \"pmids\": [\"32824403\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NMBR (neuromedin B receptor) is a Gq-coupled GPCR that, upon NMB binding, activates PLCβ1 to mobilize Ca2+ and downstream signaling cascades; in the spinal cord it cross-compensates with GRPR to maintain histaminergic itch transmission via partially overlapping interneuron circuits, is modulated by NPRC-mediated BNP cross-signaling, and in the brain drives serotonin release from dorsal raphe neurons to regulate anxiety and other behaviors; after agonist stimulation the receptor undergoes internalization-dependent homologous desensitization followed by recycling-based resensitization independent of new protein synthesis.\"\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- Papers about B7/BB1 (CD80 costimulatory molecule), BB-1 (B lymphoblast antigen/CD74), basogranulin BB1, Babesia bovis Bb-1, BRS1 (Arabidopsis), ϕBB-1 (Borrelia phage), Bifidobacterium BB1, marine bacteria BB1, Brugada syndrome BrS1, plant BRS1, etc. → EXCLUDE (alias collisions)\n- Papers about NMBR (neuromedin B receptor, BB1 bombesin receptor subtype) → KEEP\n\n**KEEP papers:** 23, 28, 32, 38, 41, 45, 48, 66, 67, 71, 74, 75, 77, 79, 81 (from main corpus); and from curated: 4, 12, 13, 16, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1991,\n      \"finding\": \"NMBR (NMB-R) was cloned from human small cell lung carcinoma cells and shown to be pharmacologically distinct from the GRP receptor, with preferential high affinity for neuromedin B over GRP; expressed in Xenopus oocytes, a GRP-R-specific antagonist blocked GRP-R responses but not NMB-R responses, demonstrating distinct pharmacology.\",\n      \"method\": \"cDNA cloning, Xenopus oocyte expression, receptor binding, pharmacological antagonist blocking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted receptor in oocytes with functional pharmacological validation\",\n      \"pmids\": [\"1655761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"NMBR signals through a pertussis toxin-insensitive G protein coupled to phospholipase C, generating inositol trisphosphate and releasing intracellular calcium; agonist binding does not increase cAMP levels, establishing PLCβ/IP3/Ca2+ as the primary signaling pathway.\",\n      \"method\": \"Stable transfection in Balb/3T3 fibroblasts, [3H]inositol phosphate assay, intracellular calcium measurement, cAMP assay\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical assays in transfected cells with multiple orthogonal readouts\",\n      \"pmids\": [\"7838118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Isoleucine-216 in transmembrane domain V (TM-V) of NMBR is critical for high-affinity NMB binding; the Ile216→Ser substitution abolished high-affinity NMB binding and severely impaired NMB-dependent inositol phosphate formation, while three other TM-V mutations did not affect binding.\",\n      \"method\": \"Site-directed mutagenesis of NMB-R/GRP-R chimeras, stable expression in Balb/3T3 fibroblasts, radioligand displacement assay, inositol phosphate assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with functional validation, multiple mutants tested\",\n      \"pmids\": [\"8392057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Distinct NMBR and GRP-R subtypes are expressed on human and rabbit colonic smooth muscle cells; antisense oligonucleotides selectively blocking NMBR mRNA translation inhibited neuromedin B-induced contraction without affecting GRP-induced contraction, demonstrating receptor-subtype-specific contractile roles.\",\n      \"method\": \"RT-PCR for receptor mRNA, antisense oligonucleotide-mediated mRNA knockdown, smooth muscle contraction assay\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — selective antisense knockdown with specific functional readout\",\n      \"pmids\": [\"8253343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"NMBR undergoes rapid homologous desensitization following agonist stimulation via receptor down-regulation mediated by internalization; recovery (resensitization) of surface NMB-R is independent of new protein synthesis and is due to recycling from an intracellular compartment, as shown by monensin (recycling inhibitor) blocking recovery but cycloheximide not affecting it.\",\n      \"method\": \"Radioligand binding assay on native C-6 glioblastoma cells and stably transfected Balb/3T3 cells, inositol phosphate/Ca2+ assays, monensin and cycloheximide treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, native and transfected cell systems, pharmacological dissection of recycling vs. synthesis\",\n      \"pmids\": [\"8163469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Four specific amino acid residues conserved in NMBR and GRP-R (but diverged in BRS-3) are critical for high-affinity NMB binding to NMBR; substituting these four residues into BRS-3 (4ΔBRS-3) increased NMB affinity to near wild-type NMBR levels, while these substitutions did not create high affinity for the non-peptide antagonist PD168368, indicating distinct structural determinants for peptide vs. non-peptide binding.\",\n      \"method\": \"Site-directed mutagenesis of BRS-3, radioligand binding assay, comparison across receptor subtypes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with rigorous binding validation across multiple receptor constructs\",\n      \"pmids\": [\"9632639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PD168368 is a potent, competitive, and selective antagonist at NMBR across human, mouse, rat, and frog species (Ki = 15–45 nM), with 30–60-fold lower affinity for GRP-R and >300-fold lower affinity for BRS-3; it inhibits NMB-induced Ca2+ and inositol phosphate responses without acting as an agonist.\",\n      \"method\": \"Radioligand binding competition assay, intracellular calcium and [3H]inositol phosphate assays across multiple species receptor variants\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multi-species, multi-cell pharmacological characterization with orthogonal functional assays\",\n      \"pmids\": [\"10454496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Rational design of BRS-3-selective agonists using conformationally restricted amino acid substitutions (specifically (R)- or (S)-amino-3-phenylpropionic acid at position 11) into the prototype bombesin analog confirmed that NMBR (and GRP-R) require distinct pharmacophore features from BRS-3 for selective high-affinity binding; BRS-3 selective agonists functioned via phospholipase C/inositol phosphate pathway.\",\n      \"method\": \"Rational peptide design, radioligand binding, [3H]inositol phosphate assay, molecular modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — structure-activity study with functional validation, but primarily focused on BRS-3 selectivity\",\n      \"pmids\": [\"11112777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NMBR-deficient female mice show impaired recovery of maternal behavior after restraint stress compared to wild-type mice, demonstrating that the NMB/NMBR pathway modulates stress resilience and maternal behavior in vivo.\",\n      \"method\": \"Nmbr knockout mice, maternal behavior scoring before and after restraint stress\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined behavioral phenotype, but no downstream molecular mechanism identified\",\n      \"pmids\": [\"12231437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NMB-R-deficient female mice exhibit decreased marble burying behavior associated with elevated 5-HT immunostaining in the dorsal raphe nucleus and downregulated 5-HT1A receptor gene expression, suggesting NMB/NMBR modulates dorsal raphe serotonergic neuron activity; 5-HT depletion with p-CPA reversed the burying deficit in KO mice.\",\n      \"method\": \"Nmbr knockout mice, marble burying behavioral test, HPLC for brain 5-HT levels, immunohistochemistry, quantitative RT-PCR, p-CPA pharmacological depletion\",\n      \"journal\": \"Brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple biological readouts and pharmacological rescue, replicated in same KO line\",\n      \"pmids\": [\"12031854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"NMBR is expressed in normal and cancerous human colonic epithelial cells and functions as a mitogen; exogenous NMB was 50–100% more efficacious than GRP in stimulating proliferation of colon cancer cell lines (Caco-2, HT-29) and also promoted proliferation of non-malignant NCM-460 colonic epithelial cells, acting in an autocrine fashion.\",\n      \"method\": \"Immunohistochemistry, Western blot with deglycosylation, cell proliferation assays in multiple colonic cell lines\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple cell lines with direct proliferation assays, protein characterization\",\n      \"pmids\": [\"15528253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Bombesin receptor BB1 (NMBR) antagonist PD176252, administered to the dorsal raphe nucleus (DRN), increased social interaction and suppressed NMB-stimulated in vivo 5-HT release in the ventral hippocampus; intra-DRN NMB agonist (NMB-30) promoted 5-HT release and suppressed social interaction, an effect blocked by a 5-HT2C (but not 5-HT1A) receptor antagonist, establishing that NMBR at the DRN drives 5-HT release to the ventral hippocampus mediating anxiogenesis.\",\n      \"method\": \"Intra-DRN microinfusion, in vivo microdialysis for hippocampal 5-HT, social interaction test, fear-potentiated startle, pharmacological receptor antagonists\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo microdialysis with site-specific microinfusion and multiple behavioral/neurochemical readouts\",\n      \"pmids\": [\"17035523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The NMBR antagonist PD168368 inhibited NMB-induced angiogenesis both in vitro and in vivo, induced cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells, and suppressed tumor growth in a xenograft model, demonstrating that NMBR signaling promotes tumor angiogenesis and cancer cell survival.\",\n      \"method\": \"In vitro angiogenesis assay, in vivo Matrigel plug angiogenesis, xenograft tumor model, cell cycle and apoptosis analysis\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro and in vivo assays with selective receptor antagonist\",\n      \"pmids\": [\"21908103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NMBR and GRPR exhibit cross-inhibitory signaling in the spinal cord to maintain normal histaminergic itch transmission: Nmbr KO mice show enhanced GRPR activity (and vice versa) without upregulation of receptor expression; double KO (Nmbr/Grpr) mice show significant deficits in histamine-evoked scratching but not chloroquine-evoked scratching, indicating GRPR alone mediates non-histaminergic itch while the two receptors compensate for each other in histaminergic itch. GRPR+ neurons act downstream of NMBR+ neurons in integrating NMB-NMBR-encoded histaminergic itch.\",\n      \"method\": \"Single and double knockout mice, intradermal pruritogen injection, scratching behavior quantification, receptor expression analysis\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double KO, multiple pruritogens, replicated behavioral readouts\",\n      \"pmids\": [\"25209280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Chicken NMBR (cNMBR) expressed in CHO cells is potently and specifically activated by cNMB (not cGRP), as monitored by luciferase reporter assays, confirming conservation of ligand selectivity across vertebrates; cNMBR is mainly expressed in the brain and testes.\",\n      \"method\": \"CHO cell expression, cell-based luciferase reporter assay, qPCR tissue expression profiling\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional receptor characterization in heterologous expression system\",\n      \"pmids\": [\"28500250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Homology modeling of NMBR followed by docking of peptoid antagonists PD168368 and PD176252 defined a pharmacophore for BB1 receptor binding; in silico screening identified structurally diverse small molecules with selective affinity for NMBR but not GRP-R (BB2), providing initial structural insight into NMBR ligand binding.\",\n      \"method\": \"Homology modeling, molecular docking, pharmacophore-based virtual screening, radioligand binding validation\",\n      \"journal\": \"Pharmaceuticals (Basel, Switzerland)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — primarily computational with limited experimental validation\",\n      \"pmids\": [\"32824403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"BNP facilitates NMB-encoded histaminergic itch through a novel NPRC-NMBR cross-signaling mechanism: NPRC (encoded by Npr3) partially co-localizes with NMBR in spinal cord laminae I-II; NPRC is required for histamine- but not chloroquine-evoked itch; BNP significantly facilitates NMB-mediated (but not GRP-mediated) scratching; BNP evoked Ca2+ responses in NMBR/NPRC HEK293 cells and dorsal horn neurons co-expressing both receptors, revealing a Gi-coupled NPRC potentiating Gq-coupled NMBR signaling.\",\n      \"method\": \"Npr3 knockout mice, behavioral itch assays, Ca2+ imaging in HEK293 cells co-expressing NMBR and NPRC, dorsal horn neuron recordings\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, heterologous co-expression Ca2+ imaging, and behavioral pharmacology providing convergent evidence\",\n      \"pmids\": [\"34919054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Steered molecular dynamics modeling of bombesin bound to NMBR and GRP-R identified receptor residues important for high affinity binding and explained differential binding affinity between the two receptors; models revealed distinct bound conformations of bombesin at BB1R vs. BB2R consistent with mutagenesis data.\",\n      \"method\": \"Steered molecular dynamics simulation, homology modeling, structure-activity analysis\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational only, no new experimental validation\",\n      \"pmids\": [\"37956803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NMBR mRNA and protein expression peaks at the onset of labor in mouse myometrium; NF-κB p65 DNA-binding activity positively correlates with NMBR mRNA expression, and NMBR expression correlates with IL-6 and HSP70 expression, suggesting NMBR participates in parturition via NF-κB p65–IL-6 signaling and may influence onset of labor by regulating HSP70 through a p65-independent pathway.\",\n      \"method\": \"Semi-quantitative RT-PCR, Western blot, NF-κB p65 DNA-binding activity assay (NoShift kit) across pregnancy stages\",\n      \"journal\": \"Zhong nan da xue xue bao. Yi xue ban\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — correlational evidence between receptor expression and signaling molecules, no direct mechanistic manipulation\",\n      \"pmids\": [\"19587437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NMB/NMBR signaling restricts H9N2 influenza virus replication by potentiating IFN-β production; mechanistically, NMBR activation upregulates TRIM25 (an E3 ubiquitin ligase) to target viral NS1 protein, and engages a positive feedback loop with the RIG-I pathway by enhancing K63-linked ubiquitination of RIG-I while transcriptionally repressing the deubiquitinase CYLD, resulting in augmented JAK-STAT1 signaling and increased ISG15 expression.\",\n      \"method\": \"NMB treatment and NMBR overexpression/knockdown in A549 cells and mouse lungs, viral replication assays, IFN-β ELISA, TRIM25 and CYLD expression analysis, ubiquitination assays, STAT1 phosphorylation\",\n      \"journal\": \"Veterinary microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple mechanistic steps validated with gain- and loss-of-function in cell and animal models\",\n      \"pmids\": [\"41242095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NMB binding to NMBR in goat granulosa cells activates PLCβ1, triggering ER Ca2+ release and raising cytosolic Ca2+ while alleviating ER stress; NMBR signaling strengthens mitochondria-associated ER membrane (MAM) formation via the IRE1α–IP3R–VDAC1 axis, facilitating Ca2+ transfer into mitochondria, enhancing mitochondrial membrane potential, respiratory chain complex activities, and ATP production, thereby promoting granulosa cell proliferation. An NMBR antagonist abolished these effects.\",\n      \"method\": \"Exogenous NMB treatment, NMBR antagonist, Ca2+ imaging, cell cycle analysis (S-phase fraction), CCNE1/CDK expression, mitochondrial membrane potential, ATP assay, MAM formation analysis\",\n      \"journal\": \"Journal of ovarian research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal mechanistic readouts with pharmacological validation using NMBR antagonist\",\n      \"pmids\": [\"41257985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Bombesin stimulates dorsal raphe nucleus serotonergic neurons in vivo via a mechanism involving NMBR (BB1 receptor); intravenous Tat-bombesin increased 5-HT neuron firing activity, and the NMBR antagonist PD176252 had the opposite effect, confirming that GRP/bombesin regulates 5-HT neurotransmission through BB1 receptors.\",\n      \"method\": \"In vivo single-unit electrophysiology of dorsal raphe 5-HT neurons, Tat-bombesin administration, PD176252 antagonist\",\n      \"journal\": \"General physiology and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo electrophysiology with pharmacological antagonism, consistent with prior microdialysis evidence\",\n      \"pmids\": [\"40114617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Bombesin ameliorates visceral hypersensitivity and colonic hyperpermeability in LPS- and CRF-induced IBS rat models via BB1 (NMBR) receptor-dependent mechanisms; effects were abolished by BB1 antagonism and reproduced by BB1 receptor activation but not BB2 activation. Mechanistic pathways involve AMPK, GABAA, nitric oxide, opioid, peripheral CRF receptor subtype 2, neurotensin receptor 1, and central orexin/dopamine D2/muscarinic receptor signaling, and suppression of IL-1β and preservation of occludin expression.\",\n      \"method\": \"IBS rat models (LPS and CRF), EMG recording of visceral pain, colonic permeability (Evans blue), occludin immunoblot, IL-1β ELISA, selective BB1/BB2 agonists and antagonists\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo models with receptor-selective pharmacology and mechanistic pathway dissection\",\n      \"pmids\": [\"41548687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Photostimulation of parafacial NMB neurons or preBötzinger Complex (preBötC) NMBR neurons elicits ectopic sighs; however, ectopic sighs can also be produced without involvement of NMB peptide or NMBR (via preBötC SST neuron activation even in the presence of NMBR and GRPR antagonists), indicating NMBR-expressing neurons participate in but are not exclusively required for sigh generation, and that preBötC SST neurons are downstream elements converting normal breaths to sighs.\",\n      \"method\": \"Optogenetic photostimulation of NMB/NMBR neurons, chemogenetic and optogenetic activation of preBötC SST neurons, NMBR/GRPR antagonist pharmacology in vivo\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — circuit-level optogenetic and chemogenetic dissection in vivo\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NMBR is a Gq-coupled seven-transmembrane G protein-coupled receptor that binds neuromedin B with high affinity (determined critically by Ile216 in TM-V and four conserved residues shared with GRP-R), activates PLCβ/IP3/Ca2+ signaling (without cAMP elevation), undergoes agonist-induced homologous desensitization via internalization and recycling, and mediates diverse physiological functions including spinal cord itch transmission (cross-inhibiting with GRPR via an NPRC co-receptor mechanism), anxiogenesis through dorsal raphe 5-HT release, sigh generation in the preBötzinger Complex, granulosa cell proliferation via MAM-mediated mitochondrial Ca2+ transfer, antiviral innate immunity through RIG-I/TRIM25/JAK-STAT1 potentiation, and gut-brain axis regulation of visceral sensitivity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NMBR (neuromedin B receptor, BB1) is a Gq-coupled GPCR that transduces NMB signaling through PLCβ1-mediated Ca²⁺ mobilization to regulate itch sensation, serotonergic neurotransmission, stress-related behavior, and cellular proliferation. In the spinal cord dorsal horn, NMBR cooperates with GRPR through cross-compensatory signaling to maintain histaminergic itch transmission, with GRPR⁺ neurons acting downstream of NMBR⁺ neurons, and BNP potentiates NMB-NMBR signaling via NPRC-mediated cross-talk [PMID:25209280, PMID:34919054]. In the dorsal raphe nucleus, NMBR activation drives serotonin release and 5-HT neuron firing, linking it to anxiety-related circuits through 5-HT2C receptor signaling [PMID:17035523, PMID:40114617]. Following agonist stimulation, NMBR undergoes internalization-dependent homologous desensitization and resensitizes via recycling from intracellular compartments independently of de novo protein synthesis [PMID:8163469].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing how NMBR is regulated after activation resolved the basic question of receptor trafficking: the receptor internalizes upon agonist binding and recycles back to the surface without requiring new protein synthesis, distinguishing it from receptors that resensitize via de novo synthesis.\",\n      \"evidence\": \"Radioligand binding, inositol phosphate assays, and Ca²⁺ measurements in native C-6 glioblastoma cells and NMB-R-transfected Balb/3T3 fibroblasts with monensin/cycloheximide dissection\",\n      \"pmids\": [\"8163469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase(s) mediating phosphorylation-dependent desensitization not identified\", \"Endosomal sorting machinery for NMBR recycling undefined\", \"Whether arrestin recruitment is required was not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Knockout studies revealed that NMBR modulates serotonergic tone in the dorsal raphe and stress-dependent maternal behavior, establishing a CNS role beyond peripheral actions.\",\n      \"evidence\": \"NMB-R knockout mice assessed by marble burying, maternal behavior after restraint stress, HPLC brain 5-HT measurement, and qRT-PCR for 5-HT1A\",\n      \"pmids\": [\"12031854\", \"12231437\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking NMBR loss to elevated dorsal raphe 5-HT not established\", \"Only female mice tested for maternal behavior phenotype\", \"No rescue experiment to confirm cell-autonomous requirement\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Direct in vivo evidence showed NMBR activation in the dorsal raphe nucleus drives serotonin release into the ventral hippocampus and produces anxiogenic behavior dependent on 5-HT2C receptors, placing NMBR within a defined neurocircuit for anxiety.\",\n      \"evidence\": \"Intra-DRN microinfusion of NMB with in vivo microdialysis of 5-HT and pharmacological receptor antagonism across multiple anxiety paradigms\",\n      \"pmids\": [\"17035523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of NMBR-expressing DRN cell types not resolved\", \"Whether endogenous NMB release in DRN regulates basal anxiety not tested\", \"Downstream intracellular signaling in DRN neurons unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Genetic epistasis demonstrated that NMBR and GRPR cross-compensate to maintain histaminergic itch, with NMB signaling exclusively through NMBR and GRPR⁺ neurons integrating NMBR-encoded itch downstream — resolving how two bombesin receptors cooperate in spinal itch circuits.\",\n      \"evidence\": \"Single and double Nmbr/Grpr knockout mice with intradermal pruritogen injection and scratch quantification\",\n      \"pmids\": [\"25209280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of cross-compensation (not receptor upregulation) remains unknown\", \"Circuit connectivity between NMBR⁺ and GRPR⁺ interneurons not mapped at synaptic level\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that BNP potentiates NMB-NMBR signaling through NPRC cross-talk revealed an unexpected mechanism by which a natriuretic peptide receptor modulates Gq-coupled itch signaling in the dorsal horn.\",\n      \"evidence\": \"Npr3 KO mice, Ca²⁺ imaging in HEK293 cells co-expressing NMBR and NPRC, and behavioral pruritogen assays\",\n      \"pmids\": [\"34919054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which NPRC potentiates NMBR-coupled PLCβ signaling unresolved\", \"Whether NPRC-NMBR cross-talk occurs in contexts other than itch is unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple studies expanded NMBR's downstream effector repertoire: NMB-NMBR activates PLCβ1-ER Ca²⁺ release and strengthens MAMs via the IRE1α–IP3R–VDAC1 axis to boost mitochondrial function, restricts influenza replication through TRIM25-mediated NS1 degradation and RIG-I ubiquitination, drives 5-HT neuron firing in the DRN, and ameliorates visceral hypersensitivity via gut-brain pathways.\",\n      \"evidence\": \"Goat granulosa cell Ca²⁺ imaging and mitochondrial assays; A549 cell and mouse lung viral replication with NMBR overexpression/knockdown; in vivo DRN electrophysiology; rat IBS models with BB1-selective pharmacology\",\n      \"pmids\": [\"41257985\", \"41242095\", \"40114617\", \"41548687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MAM-strengthening mechanism is from a non-human granulosa cell system and lacks in vivo confirmation\", \"Antiviral TRIM25/RIG-I pathway described only for H9N2 virus in single lab\", \"Gut-brain pathway components activated by BB1 in IBS are inferred from antagonist blockade without direct NMBR manipulation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of NMB selectivity for NMBR over GRPR, the identity and circuitry of NMBR-expressing neurons in brain regions beyond DRN, the molecular mechanism of GRPR-NMBR cross-compensation, and whether NMBR's antiviral and metabolic roles are physiologically relevant in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No experimentally determined NMBR structure available\", \"Cross-compensation mechanism between NMBR and GRPR at the intracellular signaling level unresolved\", \"In vivo relevance of NMBR-mediated antiviral and mitochondrial functions not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 2, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 6, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 2, 8]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [1, 3, 5, 12]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NMB\",\n      \"GRPR\",\n      \"NPR3\",\n      \"PLCB1\",\n      \"TRIM25\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"NMBR (BB1 receptor) is a Gq-coupled G protein-coupled receptor that selectively binds neuromedin B with high affinity to activate phospholipase C/IP3/Ca²⁺ signaling, mediating diverse physiological processes including itch transmission, anxiety-related behavior, respiratory patterning, cellular proliferation, and visceral sensitivity. Cloned from human small cell lung carcinoma cells, NMBR is pharmacologically distinct from the related GRP receptor (BB2), with ligand selectivity critically determined by Ile216 in transmembrane domain V and four conserved residues shared with GRP-R [PMID:1655761, PMID:8392057, PMID:9632639]. In the spinal cord, NMBR mediates histaminergic itch through a cross-inhibitory relationship with GRPR, potentiated by a Gi-coupled NPRC co-receptor mechanism that facilitates NMB-encoded signaling [PMID:25209280, PMID:34919054]. In the dorsal raphe nucleus, NMBR activation drives serotonin release to the ventral hippocampus to promote anxiogenic behavior, while peripheral NMBR signaling promotes granulosa cell and colonic epithelial cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer and autocrine mitogenic pathways, respectively [PMID:17035523, PMID:41257985, PMID:15528253].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Molecular cloning of NMBR from human SCLC cells established it as a receptor pharmacologically distinct from GRP-R, resolving the question of whether bombesin-family peptides acted through a single receptor or multiple subtypes.\",\n      \"evidence\": \"cDNA cloning, Xenopus oocyte expression with radioligand binding and subtype-selective antagonist blockade\",\n      \"pmids\": [\"1655761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural information for the receptor\", \"Downstream signaling pathway not yet defined\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of PLC/IP3/Ca²⁺ as the primary NMBR signaling cascade (with no cAMP involvement) and of Ile216 in TM-V as a critical determinant of NMB binding selectivity established both the signaling mechanism and structural basis of ligand discrimination.\",\n      \"evidence\": \"Stable transfection in Balb/3T3 fibroblasts with inositol phosphate, Ca²⁺, and cAMP assays; site-directed mutagenesis of NMB-R/GRP-R chimeras with radioligand binding\",\n      \"pmids\": [\"7838118\", \"8392057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein identity (Gq vs. G11) not directly determined\", \"Role of other TM domains in ligand binding uncharacterized\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstration that NMBR undergoes rapid agonist-induced internalization followed by recycling-dependent resensitization (independent of new protein synthesis) established the receptor's desensitization mechanism.\",\n      \"evidence\": \"Radioligand binding in C-6 glioblastoma and Balb/3T3 cells with monensin (recycling inhibitor) and cycloheximide treatment\",\n      \"pmids\": [\"8163469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases mediating receptor phosphorylation/internalization not identified\", \"β-arrestin involvement not tested\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Transfer of four conserved NMBR/GRP-R residues into BRS-3 conferred near-wild-type NMB affinity, pinpointing the minimal structural determinants for peptide ligand recognition across the bombesin receptor family.\",\n      \"evidence\": \"Site-directed mutagenesis of BRS-3, radioligand binding across receptor constructs\",\n      \"pmids\": [\"9632639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of non-peptide antagonist binding shown to differ but not fully mapped\", \"No crystal or cryo-EM structure available\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Characterization of PD168368 as a potent, selective NMBR antagonist across multiple species provided a critical pharmacological tool for dissecting NMBR function in vivo.\",\n      \"evidence\": \"Multi-species radioligand binding competition and functional Ca²⁺/IP3 assays\",\n      \"pmids\": [\"10454496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo selectivity and pharmacokinetics not fully profiled\", \"No structural basis for antagonist selectivity\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Nmbr-knockout mouse studies linked NMBR to serotonergic modulation in the dorsal raphe and stress-related behaviors, revealing its CNS role beyond peripheral peptide signaling.\",\n      \"evidence\": \"Nmbr KO mice with marble burying behavior, brain 5-HT immunohistochemistry, 5-HT1A qRT-PCR, and p-CPA rescue; separate KO study of maternal behavior after restraint stress\",\n      \"pmids\": [\"12031854\", \"12231437\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct electrophysiological evidence of NMBR action on 5-HT neurons not yet shown\", \"Molecular mechanism linking NMBR to 5-HT1A downregulation unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Site-specific microinfusion and microdialysis established that NMBR activation in the dorsal raphe nucleus directly drives serotonin release to the ventral hippocampus, mediating anxiogenic behavior through downstream 5-HT2C receptors.\",\n      \"evidence\": \"Intra-DRN microinfusion of NMB agonist and BB1 antagonist, in vivo microdialysis for hippocampal 5-HT, social interaction and fear-potentiated startle tests\",\n      \"pmids\": [\"17035523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NMBR acts directly on 5-HT neurons or via interneurons not resolved\", \"Translational relevance to human anxiety not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Genetic epistasis using single and double Nmbr/Grpr knockout mice revealed that NMBR and GRPR cross-inhibit to maintain normal histaminergic itch, with GRPR+ neurons acting downstream of NMBR+ neurons, defining a spinal itch circuit hierarchy.\",\n      \"evidence\": \"Nmbr, Grpr, and double KO mice with intradermal pruritogen injection and scratching quantification\",\n      \"pmids\": [\"25209280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of cross-inhibition not defined\", \"Identity of interneurons connecting NMBR+ to GRPR+ neurons unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that NPRC co-localizes with NMBR in spinal cord laminae I–II and that BNP potentiates NMB/NMBR Ca²⁺ signaling through Gi-coupled NPRC revealed a novel cross-receptor mechanism facilitating histaminergic itch transmission.\",\n      \"evidence\": \"Npr3 KO mice, behavioral itch assays, Ca²⁺ imaging in HEK293 cells co-expressing NMBR/NPRC, dorsal horn neuron recordings\",\n      \"pmids\": [\"34919054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling intermediates linking Gi (NPRC) to Gq (NMBR) potentiation not identified\", \"Whether this mechanism operates outside the spinal cord unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple studies expanded NMBR's functional repertoire: antiviral innate immunity via RIG-I/TRIM25/JAK-STAT1 potentiation, granulosa cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer, dorsal raphe 5-HT neuron activation by in vivo electrophysiology, and visceral hypersensitivity regulation in IBS models through BB1-selective mechanisms.\",\n      \"evidence\": \"NMBR overexpression/knockdown in A549 cells and mouse lungs with viral replication and ubiquitination assays; NMB treatment of goat granulosa cells with Ca²⁺ imaging and MAM analysis; in vivo single-unit electrophysiology of dorsal raphe neurons; IBS rat models with BB1-selective pharmacology\",\n      \"pmids\": [\"41242095\", \"41257985\", \"40114617\", \"41548687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antiviral role demonstrated only for H9N2 influenza; breadth across other viruses unknown\", \"MAM mechanism shown in goat granulosa cells; conservation in human not confirmed\", \"IBS model pharmacology involves many downstream pathways; direct NMBR effectors not fully delineated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No experimental three-dimensional structure of NMBR has been determined; the molecular basis of Gq coupling, β-arrestin recruitment kinetics, and the precise circuit identities of NMBR-expressing neurons in itch and respiratory circuits remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of NMBR\", \"β-arrestin and GRK specificity not experimentally determined\", \"Cell-type-specific transcriptomic identity of spinal NMBR+ neurons incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NMB\", \"GRPR\", \"NPR3\", \"TRIM25\", \"PLCβ1\"],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I made an error in the pathway section — I used a GO term instead of a Reactome pathway ID. Let me correct that.\n\n```json\n{\n  \"mechanistic_narrative\": \"NMBR (BB1 receptor) is a Gq-coupled G protein-coupled receptor that selectively binds neuromedin B with high affinity to activate phospholipase C/IP3/Ca²⁺ signaling, mediating diverse physiological processes including itch transmission, anxiety-related behavior, respiratory patterning, cellular proliferation, and visceral sensitivity. Cloned from human small cell lung carcinoma cells, NMBR is pharmacologically distinct from the related GRP receptor (BB2), with ligand selectivity critically determined by Ile216 in transmembrane domain V and four conserved residues shared with GRP-R [PMID:1655761, PMID:8392057, PMID:9632639]. In the spinal cord, NMBR mediates histaminergic itch through a cross-inhibitory relationship with GRPR, potentiated by a Gi-coupled NPRC co-receptor mechanism that facilitates NMB-encoded signaling [PMID:25209280, PMID:34919054]. In the dorsal raphe nucleus, NMBR activation drives serotonin release to the ventral hippocampus to promote anxiogenic behavior, while peripheral NMBR signaling promotes granulosa cell and colonic epithelial cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer and autocrine mitogenic pathways, respectively [PMID:17035523, PMID:41257985, PMID:15528253].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Molecular cloning of NMBR from human SCLC cells established it as a receptor pharmacologically distinct from GRP-R, resolving the question of whether bombesin-family peptides acted through a single receptor or multiple subtypes.\",\n      \"evidence\": \"cDNA cloning, Xenopus oocyte expression with radioligand binding and subtype-selective antagonist blockade\",\n      \"pmids\": [\"1655761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural information for the receptor\", \"Downstream signaling pathway not yet defined\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of PLC/IP3/Ca²⁺ as the primary NMBR signaling cascade (with no cAMP involvement) and of Ile216 in TM-V as a critical determinant of NMB binding selectivity established both the signaling mechanism and structural basis of ligand discrimination.\",\n      \"evidence\": \"Stable transfection in Balb/3T3 fibroblasts with inositol phosphate, Ca²⁺, and cAMP assays; site-directed mutagenesis of NMB-R/GRP-R chimeras with radioligand binding\",\n      \"pmids\": [\"7838118\", \"8392057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein identity (Gq vs. G11) not directly determined\", \"Role of other TM domains in ligand binding uncharacterized\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstration that NMBR undergoes rapid agonist-induced internalization followed by recycling-dependent resensitization (independent of new protein synthesis) established the receptor's desensitization mechanism.\",\n      \"evidence\": \"Radioligand binding in C-6 glioblastoma and Balb/3T3 cells with monensin (recycling inhibitor) and cycloheximide treatment\",\n      \"pmids\": [\"8163469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinases mediating receptor phosphorylation/internalization not identified\", \"β-arrestin involvement not tested\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Transfer of four conserved NMBR/GRP-R residues into BRS-3 conferred near-wild-type NMB affinity, pinpointing the minimal structural determinants for peptide ligand recognition across the bombesin receptor family.\",\n      \"evidence\": \"Site-directed mutagenesis of BRS-3, radioligand binding across receptor constructs\",\n      \"pmids\": [\"9632639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of non-peptide antagonist binding shown to differ but not fully mapped\", \"No crystal or cryo-EM structure available\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Characterization of PD168368 as a potent, selective NMBR antagonist across multiple species provided a critical pharmacological tool for dissecting NMBR function in vivo.\",\n      \"evidence\": \"Multi-species radioligand binding competition and functional Ca²⁺/IP3 assays\",\n      \"pmids\": [\"10454496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo selectivity and pharmacokinetics not fully profiled\", \"No structural basis for antagonist selectivity\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Nmbr-knockout mouse studies linked NMBR to serotonergic modulation in the dorsal raphe and stress-related behaviors, revealing its CNS role beyond peripheral peptide signaling.\",\n      \"evidence\": \"Nmbr KO mice with marble burying behavior, brain 5-HT immunohistochemistry, 5-HT1A qRT-PCR, and p-CPA rescue; separate KO study of maternal behavior after restraint stress\",\n      \"pmids\": [\"12031854\", \"12231437\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct electrophysiological evidence of NMBR action on 5-HT neurons not yet shown\", \"Molecular mechanism linking NMBR to 5-HT1A downregulation unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Site-specific microinfusion and microdialysis established that NMBR activation in the dorsal raphe nucleus directly drives serotonin release to the ventral hippocampus, mediating anxiogenic behavior through downstream 5-HT2C receptors.\",\n      \"evidence\": \"Intra-DRN microinfusion of NMB agonist and BB1 antagonist, in vivo microdialysis for hippocampal 5-HT, social interaction and fear-potentiated startle tests\",\n      \"pmids\": [\"17035523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NMBR acts directly on 5-HT neurons or via interneurons not resolved\", \"Translational relevance to human anxiety not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Genetic epistasis using single and double Nmbr/Grpr knockout mice revealed that NMBR and GRPR cross-inhibit to maintain normal histaminergic itch, with GRPR+ neurons acting downstream of NMBR+ neurons, defining a spinal itch circuit hierarchy.\",\n      \"evidence\": \"Nmbr, Grpr, and double KO mice with intradermal pruritogen injection and scratching quantification\",\n      \"pmids\": [\"25209280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of cross-inhibition not defined\", \"Identity of interneurons connecting NMBR+ to GRPR+ neurons unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that NPRC co-localizes with NMBR in spinal cord laminae I–II and that BNP potentiates NMB/NMBR Ca²⁺ signaling through Gi-coupled NPRC revealed a novel cross-receptor mechanism facilitating histaminergic itch transmission.\",\n      \"evidence\": \"Npr3 KO mice, behavioral itch assays, Ca²⁺ imaging in HEK293 cells co-expressing NMBR/NPRC, dorsal horn neuron recordings\",\n      \"pmids\": [\"34919054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling intermediates linking Gi (NPRC) to Gq (NMBR) potentiation not identified\", \"Whether this mechanism operates outside the spinal cord unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple studies expanded NMBR's functional repertoire: antiviral innate immunity via RIG-I/TRIM25/JAK-STAT1 potentiation, granulosa cell proliferation via MAM-mediated mitochondrial Ca²⁺ transfer, dorsal raphe 5-HT neuron activation by in vivo electrophysiology, and visceral hypersensitivity regulation in IBS models through BB1-selective mechanisms.\",\n      \"evidence\": \"NMBR overexpression/knockdown in A549 cells and mouse lungs with viral replication and ubiquitination assays; NMB treatment of goat granulosa cells with Ca²⁺ imaging and MAM analysis; in vivo single-unit electrophysiology of dorsal raphe neurons; IBS rat models with BB1-selective pharmacology\",\n      \"pmids\": [\"41242095\", \"41257985\", \"40114617\", \"41548687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Antiviral role demonstrated only for H9N2 influenza; breadth across other viruses unknown\", \"MAM mechanism shown in goat granulosa cells; conservation in human not confirmed\", \"IBS model pharmacology involves many downstream pathways; direct NMBR effectors not fully delineated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No experimental three-dimensional structure of NMBR has been determined; the molecular basis of Gq coupling selectivity, β-arrestin recruitment kinetics, and the precise circuit identities of NMBR-expressing neurons in itch and respiratory circuits remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of NMBR\", \"β-arrestin and GRK specificity not experimentally determined\", \"Cell-type-specific transcriptomic identity of spinal NMBR+ neurons incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 6, 16]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [9, 11, 13, 21]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NMB\", \"GRPR\", \"NPR3\", \"TRIM25\", \"PLCβ1\"],\n    \"other_free_text\": []\n  }\n}\n```"}