Endogenous Neuroactive Extracellular Signal Transducers


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The first list below includes endogenous neuroactive extracellular signal transducers with known receptors. The list is composed of neurotransmitters, neuromodulators, neuropeptides, neurosteroids, and neuroactive hormones. The list does not include growth factors, cytokines, and intracellular second messengers; note that I have classified insulin as a growth factor. In all but a few cases (in which available information is lacking or misleading), the substances listed are known to or very likely to affect neurons in the human brain. For the most part, I have neglected to include non-receptor binding sites such as enzymes and voltage-gated ion channels. Ligand groups marked with an asterisk (*) have been grouped together due to the difficulty of matching each ligand with its specific receptors; the receptors listed for such groups are not necessarily affected by each of the ligands listed. Do not assume that the list is comprehensive; many endogenous ligands and receptors have not yet been identified or characterized. You are strongly encouraged to report any errors or suggestions. -- Shawn Thomas

Please note that "G5" represents a link to a PDF file from Neuropsychopharmacology: The Fifth Generation of Progress; "G4" represents a link to an HTML file from Psychopharmacology - The Fourth Generation of Progress (published by the American College of Neuropsychopharmacology).

(Updated 1/12/06)

Endogenous Ligands








Acetylcholine Acetylcholine receptors [muscarinic: M1, M2, M3, M4, M5; nicotinic][Muscarinic] [Nicotinic] [G5] [G4: Muscarinic] [G4: Nicotinic] M1: 11q13; M2: 7q35-q36; M3: 1q41-q44; M4: 11p12-p11.2; M5: 15q26
Catestatin [an endogenous noncompetitive antagonist]Acetylcholine receptors [nicotinic][Catestatin]
AdenosineAdenosine receptors [A1, A2A, A2B, A3][Adenosine receptors] [Purine and pyrimidine receptors] [G5] A1: 1q32.1; A2A: 22q11.2; A2B: 10q25.3-q26.3; A3: 1p21-p13
Inosine [an adenosine metabolite]Adenosine A1, A3 receptors[Inosine] [Adenosine receptors] A1: 1q32.1; A3: 1p21-p13
Epinephrine [aka adrenaline], norepinephrine [aka noradrenaline] Adrenoceptors: [alpha-1A, alpha-1B, alpha-1D, alpha-2A, alpha-2B, alpha-2C, beta-1, beta-2, beta-3], D4 receptors [G5] [G4] ["Epinephrine and norepinephrine act as potent agonists at the recombinant human dopamine D4 receptor."] alpha-1A: 8p21; alpha-1B: 5q33; alpha-1D: 20p13; alpha-2A: 10q24-q26; alpha-2B: Chr.2; alpha-2C: 4p16.1; beta-1: 10q24-q26; beta-2: 5q32-q34; beta-3: 8p12-p11.2
Lipoxin A4 (LXA4)ALX receptors (aka LXA4 receptors)[Leukotriene and lipoxin receptors] [LXA4 and sleep]ALX receptor: Chr.19
Angiotensin II (Ang II), angiotensin III (Ang III)Angiotensin receptors [AT1A, AT1B, AT2][Angiotensin II]AT1A/AT1B: 3q21-q25; AT2: Xq22-q23
ApelinAPJ receptors [APJ][Apelin] [Apelin] Apelin: Xq25-q26.3; APJ: 11q12
KiSS-1 AXOR12 receptors (aka GPR54 receptors)[AXOR12] [Kisspeptins] [Metastin exhibits potent LH releasing activity]

KiSS-1: 1q32; GPR54: 19p13.3

Diazepam-binding inhibitor (DBI), octadecaneuropeptide (ODN), COOH-terminal octapeptide fragment of ODN, triakontatetraneuropeptide [all are inverse agonists at benzodiazepine receptors; triakontatetraneuropeptide may not be active at central-type benzodiazepine receptors]Benzodiazepine binding sites [central and peripheral][COOH-terminal octapeptide, ODN] [DBI] [Peripheral benzodiazepine receptors] [Triakontatetraneuropeptide]Peripheral benzodiazepine receptor: 22q13.31
PorphyrinsBenzodiazepine receptors [peripheral][Peripheral benzodiazepine receptors]Peripheral benzodiazepine receptor: 22q13.31
Gastrin-releasing peptide (GRP), neuromedin B (NMB), neuromedin C (NMC) Bombesin-like peptide receptors: gastrin-releasing peptide receptor [GRPR], neuromedin B receptor [NMBR], bombesin-like receptor 3 [BRS3][NMBR]

GRP: 18q21; NMB: 15q22-qter; GRPR: Xp22.3-p21.2; NMBR: 6q21-qter; BRS3: Xq26-q28

Anaphylatoxin C3a C3a anaphylatoxin receptors [C3aR][Neuronal anaphylatoxin receptors] C3a: 19p13.3-p13.2; C3aR: ???
Anaphylatoxin C5aC5a anaphylatoxin receptors [C5aR] [Neuronal anaphylatoxin receptors] C5aR: Chr.19
*Calcitonin, alpha-CGRP, beta-CGRP, amylin [aka islet amyloid polypeptide (IAPP)], adrenomedullin (please view the first link provided for a description of the complex relationships between these ligands and their receptors) Calcitonin, amylin, CGRP, and adrenomedullin receptors [CL, CTR][Calcitonin, amylin, CGRP, adrenomedullin] [Adrenomedullin]Calcitonin, alpha-CGRP: 11p15.2-p15.1; beta-CGRP: 11p15.2-p15.1; amylin: 12p12.3-p12.1; adrenomedullin: 11p15.4; CL: 2q31-q32; CTR: 7q21.3
Anandamide [aka arachidonoylethanolamide], 2-arachidonoylglycerol, 2-arachidonylglyceryl ether [aka noladin ether], virodhamine, N-Arachidonoyldopamine (NADA) Cannabinoid receptors [CB1, CB2] (note that CB2 receptors are not found in the brain)[Cannabinoid Receptors] [Virodhamine] [NADA] [G5] CB1: 6q14-q15; CB2: Chr.1
Cholecystokinin (CCK)-4, CCK-5, CCK-7, CCK-7 sulfate, CCK-8, CCK-8 sulfate, CCK-12, CCK-22, CCK-33, CCK-39, CCK-58, gastrinCholecystokinin receptors [CCK1 (CCK-A), CCK2 (CCK-B)][Cholecystokinin] [G4]CCK: 3pter-p21; Gastrin: 17q21; CCK1: 4p15.2-p15.1; CCK2: 11p15.5-p15.4
Corticotropin-releasing factor (CRF) [aka corticotropin-releasing hormone (CRH)], urocortin [aka urotensin I] Corticotropin-releasing factor receptors [CRF1, CRF2][CRF] [G5] [G4] CRF: 8q13; Urocortin: Chr.2; CRF1: 17q12-q22; CRF2: 7p21-p15
Stresscopin (SCP) [aka urocortin III], stresscopin-related peptide (SRP) [aka urocortin II or urocortin-related peptide (URP)]CRF2 receptors [Stresscopin] [SCP/SRP]SCP: ???; SRP: 3p21.3; CRF2: 7p21-p15
Cysteinyl leukotrienes: LTC4, LTD4, LTE4Cysteinyl-leukotriene receptors [CYSLT1, CYSLT2][Leukotriene Receptors]CYSLT1: Xq13-q21; CYSLT2: 13q14
Dopamine Dopamine receptors [D1, D2, D3, D4, D5][Dopamine] [Dopamine/Neurotensin] [G5] D1: 5q35.1; D2: 11q23; D3: 3q13.3; D4: 11p15.5; D5: 4p16.1-p15.3
Endothelin-1 (ET-1) , ET-2, ET-3 Endothelin receptors [ETA, ETB][Endothelin]ET-1: 6p24-p23; ET-2: 1p34; ET-3: 20q13.2-q13.3; ETA: Chr.4; ETB: 13q22
Follicle-stimulating hormone (FSH) [aka follitropin]Follicle-stimulating hormone receptors [FSHR][FSH] [Gonadotropins] FSH: 11p13; FSHR: 2p21-p16
GABA [aka gamma-aminobutyric acid]
GABA receptors [GABA-A, GABA-B] [GABA-A] [GABA-B] [G5] GABAB1: ???; GABAB2: 9q22.1
Galanin, galanin-like peptide (GALP) Galanin receptors [GALR1, GALR2, GALR3][G4] [Human GALP is located on chromosome 19]Galanin: 11q13.3-q13.5; GALR1: 18q23; GALR2: 17q25.3; GALR3: 22q12.2-q13.1
Gastric inhibitory polypeptide (GIP) [aka glucose-dependent insulinotropic peptide]Gastric inhibitory polypeptide receptors [GIPR][Glucagon receptor family]
[PACAP/Glucagon superfamily]
GIP: 17q21.3-q22; GIPR: 19q13.3
gamma-Hydroxybutyrate (GHB), 4-Hydroxy-trans-2-nonenoic acidGHB receptors[GHB] [4-Hydroxy-trans-2-nonenoic acid]
GlucagonGlucagon receptors [GCGR][Glucagon receptor family] [PACAP/Glucagon superfamily] Glucagon: 2q36-q37; GCGR: 17q25
Glucagon-like peptide-1 (GLP-1)GLP-1 receptors [GLP1R][Glucagon-like peptides] [Glucagon receptor family] [PACAP/Glucagon superfamily]GLP1: 2q36-q37; GLP1R: 6p21
Glucagon-like peptide-2 (GLP-2) GLP-2 receptors [GLP2R] [Glucagon-like peptides] [Glucagon receptor family] [PACAP/Glucagon superfamily]GLP2: 2q36-q37; GLP2R: 17p13.3
CortisolGlucocorticoid receptors [GR], mineralocorticoid receptors [MR][Cortisol (on site link)]GR: 5q31; MR: 4q31.1
Glutamate Glutamate AMPA receptors [ionotropic receptors composed of subunits including GluR1, GluR2, GluR3, GluR4] [General] [G5] GluR1: 5q33; GluR2: 4q32-q33; GluR3: Xq25-q26; GluR4: 11q22-q23
Glutamate Glutamate kainate receptors [ionotropic receptors composed of subunits including GluR5, GluR6, GluR7, KA-1, KA-2] [Kainate] [G5] GluR5: 21q22; GluR6: 6q21; GluR7: 1p34-p33; KA-1: 11q22.3; KA-2: 19q13.2

Glutamate, quinolinate, glutathione (GSH) [see the link provided for a description of GSH's complex activity at NMDA receptors], gamma-L-Glutamylglutamate (LGG) [also a possible agonist at AMPA/kainate receptors], l-homocysteate, L-serine-O-sulfate, l-cysteine sulfate, l-cysteic acid, succinate

Glutamate NMDA receptors [ionotropic receptors composed of subunits including NR1, NR2A, NR2B, NR2C, NR2D, NR3A, NMDARA1] (eight splice variants of the NR1 subunit exist: NR1-1a, NR1-2a, NR1-3a, NR1-4a, NR1-1b, NR1-2b, NR1-3b, NR1-4b)[NMDA] [G5] [Quinolinate] [Glutathione] [gamma-L-Glutamylglutamate] [NR1 splice variants] [l-homocysteate] [L-serine-O-sulfate] [Succinate] NR1: 9q34.3; NR2A: 16p13; NR2B: 12p12; NR2C: 17q25; NR2D: 19q13.1-qter; NR3A: ???; NR3B: 19p13.3; NMDARA1: 8q24.3
Spermine, spermidine [neuromodulators at the receptors and channnels listed]Glutamate AMPA, kainate, NMDA receptors; inward rectifying K+ channels[Spermine and Spermidine]
Glutamate, L-aspartate, L-homocysteine sulfinic acid, L-homocysteic acid, L-cysteine sulfinic acid, L-cysteic acid, etc. [note that the sulphur-containing excitatory amino acids (the latter four ligands) are not equally effective agonists at all mGluRs] Metabotropic glutamate receptors [Group I: mGluR1, mGluR5; Group II: mGluR2, mGluR3; Group III: mGluR4, mGluR6, mGluR7, mGluR8][G5] [Sulphur-containing excitatory amino acids] mGluR1: 6q24; mGluR2: 3p21.2-p21.1; mGluR3: 7q21.1-q21.2; mGluR4: 6p21.3; mGluR5: ???; mGluR6: 5q35; mGluR7: 3p26.1-p25.2; mGluR8: 7q31.3-q32.1
N-Acetylaspartylglutamate (NAAG) mGluR3, NMDA receptors[N-Acetylaspartylglutamate] [NAAG is a very low potency agonist at NMDA receptors] [NAAG lacks activity at NMDA receptors on cerebellar granule neurons] [NAAG showed a 12-fold preference for mGluR3 over mGluR2 receptors expressed in CHO cells]mGluR3: 7q21.1-q21.2
Glycine, beta-alanine, taurine Glycine GlyR receptors [ionotropic receptors composed of subunits including alpha-1, alpha-2, beta][Glycine]GlyR alpha-1 subunit: 5q32; GlyR alpha-2 subunit: Xp22.1-p21.2; GlyR beta subunit: 4q31.3
Glycine, D-serine, dynorphin A(1-13), kynurenate [an endogenous antagonist at both the GlycineB binding site and the alpha7 nicotinic acetylcholine receptor]GlycineB binding site on NMDA receptors (located on the NR1 subunit)

[Glycine and NMDA] [D-serine] [Dynorphin A(1-13)] [Kynurenate]

Growth hormone-releasing hormone (GHRH) [aka growth hormone-releasing factor (GRF) or somatocrinin] GHRH receptors [GHRHR][Glucagon receptor family]
[PACAP/Glucagon superfamily]

GHRH: 20q11.2; GHRHR: 7p15-p14

Gonadotropin-releasing hormone I (GNRH I) [aka luteinizing hormone-releasing hormone (LHRH) or prolactin release-inhibiting factor (PIF)]

Gonadotropin-releasing hormone I receptors [GNRHR] (aka luteinizing hormone-releasing hormone receptors [LHRHR])

[GNRH] [G4] GNRH I : 8p21-p11.2; GNRHR: 4q21.2
Gonadotropin-releasing hormone II (GNRH II)GNRH II receptors, GNRH I receptors [GNRHR][GNRH II] [GNRH II] [GNRH II and GNRHR]GNRH2: 20p13
Sphingosylphosphorylcholine (SPC) GPR12 [GPR12] GPR12: 13q12
Neuropeptide B (NPB), neuropeptide W (NPW)GPR7 and GPR8 receptors[Neuropeptide B/Neuropeptide W] [GPR7/GPR8] [NPW and neuroendocrine regulation]GPR7: 10q11.2-q21.1; GPR8: 20q13.3
Growth hormone (GH)Growth hormone receptors [GHR][GH and NPY neurons] [GH as a neuronal rescue factor]GH: 17q22-q24; GHR: 5p13-p12
GhrelinGrowth hormone secretagogue receptor [GHSR][Ghrelin] [Ghrelin] Ghrelin: 3p26-p25; GHSR: ???
Histamine Histamine receptors [H1, H2, H3, H4][Histamine] [G5] [G4] H1: 3p21-p14; H2: ???; H3: ???; H4: 18q11.2
5-Hydroxytryptamine (5-HT) [aka serotonin] 5-Hydroxytryptamine (5-HT) receptors [5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3A/B, 5-HT4A/B/C/D, 5-HT5A, 5-HT6, 5-HT7A/B/C/D] (letters not separated by commas indicate splice variants)[G5] 5-HT1A: 5q11.2-q13; 5-HT1B: 6q13; 5-HT1D: 1p36.3-p34.3; 5-HT1E: 6q14-q15; 5-HT1F: 3p12; 5-HT2A: 13q14-q21; 5-HT2B: 2q36.3-q37.1; 5-HT2C: Xq24; 5-HT3A: 11q23.1-q23.2; 5-HT3B: 11q23.1; 5-HT4: 5q31-q33; 5-HT5A: 7q36.1; 5-HT6: 1p36-p35; 5-HT7: 10q21-q24
5-HT-moduline [an endogenous antagonist]5-HT1B receptors[5-HT-moduline] [NESP55 (Precursor Peptide)]NESP55: 20q13.2
Agmatine [also an endogenous antagonist at glutamate NMDA receptors]Imidazoline receptors [I(1), I(2)], alpha-2D-adrenoceptors[Agmatine] [Agmatine and NMDA receptors] [Agmatine and alpha-2D-adrenoceptors]I1/I2: ???
Kinins: bradykinin (BK), kallidin [aka Lys-BK], Met-Lys-BK, des-Arg9-BK, Lys-des-Arg9-BK, T-kinin [aka Ile-Ser-BK], etc. Kinin receptors [B1, B2] [B1 Receptors] [Kinin Receptors] [Neuronal Kinin Receptors] [Bradykinin is also an agonist at GPR100 receptors] B1 receptor: 14q32.1-q32.2; B2 receptor: 14q32.1-q32.2
KyotorphinKyotorphin receptors[Kyotorphin] [The kyotorphin receptor]
LeptinLeptin receptors [LEPR]Leptin: 7q31.3; LEPR: 1p31
Leukotriene B4 [aka dihydroxy-leukotriene]Leukotriene B4 receptors [BLT1, BLT2], vanilloid receptors [VR1][Leukotriene Receptors] [VR1]BLT1: 14q11.2-q12; BLT2: 14q11.2-q12
Relaxin 1 LGR7 and LGR8 receptors[Relaxin 1 and LGR7, LGR8] [Relaxin 1] Relaxin 1: 9pter-q12; LGR7: 4q32; LGR8: 13q13.1
Relaxin 3 GPCR135 receptors, GPCR142 (GPR100) receptors, LGR7 receptors

[GPCR135] [ GPCR142] [Relaxin 3 and LGR7] [Relaxin 3]

Relaxin 3: 19p13.3; LGR7: 4q32
Luteinizing hormone (LH) [aka lutropin], choriogonadotropin (CG) [aka chorionic gonadotropin]Luteinizing hormone/choriogonadotropin receptors [LHR][Lutropin/Choriogonadotropin] [Gonadotropins]LH: 19q13.32; CG: 19q13.32; LHR: 2p21
Lysophosphatidic acid (LPA)Lysophosphatidic acid (LPA) receptors [LPA1, LPA2, LPA3, LPA4 (aka GPR23)][Lysophospholipid Receptors] [LPA and the brain] [LPA4]LPA1: ???; LPA2: 19p12; LPA3: ???; LPA4: Xq13-q21.1
Angiotensin-(1-7) Mas proto-oncogene [Angiotensin-(1-7) and Mas] [Mas Knockout Mice] [G-protein-coupled receptor Mas is a physiological antagonist of the angiotensin II type 1 receptor.] Mas: 6q25.3-q26
Melanin-concentrating hormone (MCH)Melanin-concentrating hormone receptors [MCH1R, MCH2R][MCH]MCH: 12q23-q24; MCH1R: 22q13.3; MCH2R: 6q16.2-q21

alpha-Melanocyte-stimulating hormone (alpha-MSH), desacetyl-alpha-melanocyte-stimulating hormone (desacetyl-alpha-MSH), beta-melanocyte-stimulating hormone (beta-MSH)

Melanocortin (MC) receptors [MC1, MC2, MC3, MC4, MC5][desacetyl-alpha-MSH]MSH peptides: 2p23.3; MC1: 16q24.3; MC2: 18p11.2; MC3: 20q13.2; MC4: 18q22; MC5: 18p11.2
Neuropeptide EI (NEI), neuropeptide GE (NGE)Melanocortin MC1 receptors[NEI/NGE and MC1-R]NEI/NGE: 12q23-q24; MC1: 16q24.3
Adrenocorticotrophin (ACTH)Melanocortin MC2 receptors [aka adrenocorticotropin (ACTH) receptors]ACTH: 2p23.3; MC2: 18p11.2
HP-4 (aka corticostatin) [an endogenous competitive antagonist at ACTH receptors and an agonist at L-type calcium channnels]Melanocortin MC2 receptors [aka adrenocorticotropin (ACTH) receptors][HP-4] [Corticostatin and ACTH]HP-4: Chr.8; MC2: 18p11.2
gamma-melanocyte-stimulating hormone (gamma-MSH)Melanocortin MC3 receptors[gamma-MSH]gamma-MSH: 2p23.3; MC3: 20q13.2
Agouti gene-related protein (AGRP) [an endogenous inverse agonist]Melanocortin MC3, MC4 receptors[AGRP inverse agonism] [AGRP also exhibits weak activity at MC2, MC5]AGRP: 16q22; MC3: 20q13.2; MC4: 18q22
Melatonin (MLT) [aka N-acetyl-5-methoxytryptamine] Melatonin receptors [MT1 (aka Mel1a), MT2 (aka Mel1b)][Melatonin] [MT3 is the quinone reductase 2]MT1: 4q35.1; MT2: 11q21-q22
MotilinMotilin receptors [MTLR1] [Motilin and anxiety] [Motilin] Motilin: 6p21.3; MTLR1: 13q14-q21
Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP)Natriuretic peptide receptors [NPR-A, NPR-C] (BNP is a low affinity agonist at NPR-A receptors)[Natriuretic Peptides] [Natriuretic peptide receptor guanylyl cyclases] [Evidence for a novel NPR]ANP: 1p36.2; BNP: 1p36.2; NPR-A: 1q21-q22; NPR-C: 5p14-p12
Type C-natriuretic peptide (CNP)Natriuretic peptide receptors [NPR-B, NPR-C][Natriuretic Peptides] [Natriuretic peptide receptor guanylyl cyclases]CNP: 2q24-qter; NPR-B: 9p21-p12; NPR-C: 5p14-p12
Neuromedin U, neuropeptide S Neuromedin U (NMU) receptors [NMU1, NMU2]

[NMU1 and NMU2 receptors] [Neuromedin s is a novel anorexigenic hormone.] [Neuropeptide S promotes both arousal and anxiolytic-like effects]

NMU: ???; NMU1: ???; NMU2: ???
Neuropeptide Y (NPY), peptide YY (PYY), pancreatic polypeptide (PP) Neuropeptide Y receptors [Y1, Y2, Y4, Y5][NPY/PP] [G4]NPY: 7p15.1; PYY: 17q21; PPY: 17q12-q21; Y1: 4q31.3-q32; Y2: 4q31; Y4: 10q11.2-q21.2; Y5: 4q31-q32
Neurotensin, neuromedin N Neurotensin receptors [NTS1, NTS2, NTS3 (aka sortilin)] [Dopamine/Neurotensin] [G4] Neurotensin: 12q21; NT1: 20q13; NT2: ???; NT3: 1p21.3-p13.1
Xenin Neurotensin NTS1 receptors, unknown binding site [Xenin] [Xenin and NT-1] [Unknown binding site] NT1: 20q13
Neuropeptide FF (NPFF) [also an agonist at OT7T022 receptors], neuropeptide AF (NPAF), neuropeptide SF (NPSF), NPVF-derived peptidesNPFF receptors [NPFF1, NPFF2][NPFF-like peptides] [NPFF1, NPFF2] [NPFF and OT7T022]NPFF/NPAF: ???; NPFF1: 10q21; NPFF2: 4q13.2-q13.3
*beta-endorphin, Leu-enkephalin, Met-enkephalin, Met-enkephalin-Arg-Gly-Leu (MERGL), Met-Enkephalin-Arg-Phe (MERF), morphine, peptide E, peptide F, endomorphin-1, endomorphin-2, metorphamide, neo-dynorphin, dynorphin-(1-17), dynorphin A-(1-8), dynorphin B, alpha-neoendorphin, beta-neoendorphin, BAM-12P, BAM-18P, synenkephalin, beta-casomorphin, VV-hemorphin-7, LVV-hemorphin-7, LVV-hemorphin-6, VV-hemorphin-5, VV-hemorphin-4, cytochrophin-4, etc. Opioid receptors [mu1, mu2, mu3, kappa1a, kappa1b, kappa2a, kappa2b [putative], delta1, delta2, epsilon receptors] (mu1, mu2, and mu3 receptors are splice variants of the mu opioid receptor gene; genetic information on kappa and delta receptor subtypes is not yet available.)

[G5] [Receptor binding affinities] [MU3] [MU splice variants] [Endogenous morphine] [Kappa1a, kappa1b receptors] [Kappa2a, kappa2b receptors] [Delta opioid receptor] [Delta opioid receptor subtypes] [Epsilon opioid receptor] [beta-casomorphin and opioid receptors] [beta-casomorphin and lactacting women] [VV-hemorphin-7/LVV-hemorphin-7] [VV-hemorphin-7] [Hemorphins in rat tissues] [MERF, MERGL, BAM-12P in the human brain] [Metorphamide, peptide E, and BAM 18P in the rat brain] [Endomorphin-1 and endomorphin-2 in the mouse brain] [Dynorphin peptides and neoendorphins in the human brain] [Synenkephalin in the rat brain] [Cytochrophin-4] [Cytochrophin-4 and epsilon receptors] [G4]

Proenkephalin: 8q23-q24; prodynorphin: 20pter-p12.2; POMC: 2p23.3; mu: 6q24-q25; kappa: 8q11.2; delta: 1p36.1-p34.3
Orexin A, orexin B [aka hypocretins] Orexin receptors [OX1R, OX2R] (note that OX1R is moderately selective for orexin A)[Orexins]Orexin A, orexin B: 17q21; OX1R: ???; OX2R: ???
RFamide-related peptide-1 (RFRP-1), RFamide-related peptide-3 (RFRP-3), neuropeptide FF (NPFF)OT7T022 receptors [OT7T022] [RFRP-1] [RFRP immunoreactivity] [NPFF and OT7T022]
Nociceptin/orphanin FQ (N/OFQ)ORL1 receptors [aka NOP1 receptors][Orphanin FQ/Nociceptin]N/OFQ: 8p21; ORL1: ???
OxyntomodulinOxyntomodulin receptors [putative], glucagon receptors [GCGR], GLP-1 receptors [GLP1R][Oxyntomodulin] [Glucagon receptor family] GCGR: 17q25; GLP1R: 6p21
Oxytocin (OT) Oxytocin receptors [OTR][Oxytocin]Oxytocin: 20p13; OTR: 3p26.2

*ATP, UTP, ADP, UDP, ATPgammaS, UTPgammaS, 2Cl-ADP, 2MeSATP, 2MeSADP, ADPbetaS, ADPbetaF, alphabeta-meATP, betagamma-meATP, BzATP, Ap3A, Ap4A, Ap5A, Ap6A, etc.

P2X receptors [ionotropic receptors composed of subunits including P2X1, P2X2, P2X3, P2X4, P2X5, P2X6, P2X7]; P2Y receptors [P2Y1, P2Y2 (aka P2U), P2Y4, P2Y6, P2Y11, P2Y12, P2Y13]; P2D receptors [putative]; P3 receptors; P4 receptors [putative]; P2T (found on platelets); P2Z (found on mast cells and lyphocytes)

[P2X/P2Y] [Molecular Physiology of P2X Receptors] [P2X] [P2Y12] [P2Y13] [G5] [G4] [P2D] [P3]; [P4, Diadenosine polyphosphate receptors]

P2X1: 17p13.3; P2X2: ???; P2X3: 11q12; P2X4: 12q24.32; P2X5: ???; P2X7: 12q24; P2Y1: 3q25; P2Y2: 11q13.5; P2Y4: Xq13; P2Y6: 11q13.5; P2Y11: 19p13
Pituitary adenylate cyclase activating peptide (PACAP)PAC receptors [PAC1], VPAC receptors [VPAC1, VPAC2][PACAP] [VIP/PACAP] [PACAP/Glucagon superfamily] PACAP: 18p11; PAC1: 7p14; VPAC1: 3p22; VPAC2: 7q36.3
PancreastatinPancreastatin receptors[Pancreastatin] [Pancreastatin receptor] [Effects of pancreastatin on the rat brain]

Pancreastatin precursor gene: 14q32

Parathyroid hormone (PTH)Parathyroid hormone 1 receptors [PTH1], parathyroid hormone 2 receptors [PTH2][PTH]

PTH: 11p15.3-p15.1; PTH1: 3p22-p21.1; PTH2: 2q33

Parathyroid hormone-related protein (PTHrP)Parathyroid hormone 1 receptors [PTH1][PTHrP and AVP secretion]PTHrP: 12p12.1-p11.2; PTH1: 3p22-p21.1
Tuberoinfundibular peptide of 39 residues (TIP39) [TIP39 is an antagonist at PTH1 receptors]Parathyroid hormone 1 receptors [PTH1], parathyroid hormone 2 receptors [PTH2][TIP39] [TIP39 expression in the rat CNS]PTH1: 3p22-p21.1; PTH2: 2q33
Prostaglandin PGD2 PGD2 receptors (aka DP receptors)[Prostanoids] [Prostanoid receptors]PGD2 receptor: ???
Prostaglandin PGE2PGE2 receptors [EP1, EP2, EP3, EP4][Prostanoids] [Prostanoid receptors]EP1: 19p13.1; EP2: 14q22; EP3: 1p31.2; EP4: 5p13.1
Prostaglandin PGF2-alpha PGF2-alpha receptors (aka FP receptors)[Prostanoids] [Prostanoid receptors]FP receptor: 1p31.1
Prostaglandin PGI2 [aka prostacyclin]PGI2 receptors (aka IP receptors)[Prostanoids] [Prostanoid receptors]IP receptor: 19q13.3
Peptide histidine isoleucine (PHI), peptide histidine methionine (PHM), peptide histidine valine (PHV)PHI/PHV receptors [putative], VPAC receptors [VPAC1, VPAC2] (PHI and PHM bind only weakly at VPAC receptors)[PACAP/Glucagon superfamily] [PHM in the human brain] [PHI, PHV in the mouse brain] [PHI/PHV receptor in the goldfish]
PHI/PHM/PHV: 6q26-q27; VPAC1: 3p22; VPAC2: 7q36.3
Platelet-activating factor (PAF) [PAF may also inhibit GABA-A receptor activity]Platelet-activating factor receptors [PTAFR] [PAF and LTP in the dentate gyrus] [PAF and GABA-A receptors]PTAFR: 1p35-p34.3
Prokineticin 2, prokineticin 1 Prokineticin PK2 receptors [Molecular cloning and characterization of prokineticin receptors.] [Regulation of prokineticin 2 expression by light and the circadian clock.] PK2: 20p12.3; prokineticin 2: 3p21.1
ProlactinProlactin receptors [PRLR][Prolactin] [Prolactin] Prolactin: 6p22.2-p21.3; PRLR: 5p13-p12
Prolactin-releasing peptide (PrRP) [aka prolactin-releasing hormone (PRH)] (two isoforms exist: PrRP31 and PrRP20)Prolactin-releasing peptide (PrRP) receptors (aka UHR1/GPR10 receptors), NPFF2 receptors[PrRP and its receptor] [PrRP and NPFF2 receptors] [PrRP isoforms]PrRP: ???; GPR10: 10q25.3-q26; NPFF2: 4q13.2-q13.3
*Endogenous proteinase-activated receptor regulators: thrombin, trypsin, tryptase, cathepsin G, granzyme A, streptokinase-plasminogen, etc. [see the review for a larger list]Proteinase-activated receptors [PAR1, PAR2, PAR3, PAR4]

[PARs] [PARs in the rat brain] [Perspectives on PARs]

Thrombin: 11p11-q12; granzyme A: 5q11-q12; cathepsin G: 14q11.2

SecretinSecretin receptors [SR][Glucagon receptor family]
[PACAP/Glucagon superfamily]
Secretin: 11p15.5; secretin receptor: 2q14.1
Somatostatin-14 (S-14), somatostatin-28 (S-28), cortistatin (CST-14) Somatostatin receptors [SST1, SST2, SST3, SST4, SST5][G4]

Somatostatin: 3q28; cortistatin: 1p36; SST1: 14q13; SST2: 17q24; SST3: 22q13.1; SST4: 20p11.2; SST5: 16p13.3

Sphingosine-1-phosphate (S1P), dihydro-sphingosine 1-phosphate (DHS1P) Sphingosine-1-phosphate (S1P) receptors [S1P1, S1P2, S1P3, S1P4, S1P5], GPR3, GPR6, GPR12, GPR63 [Lysophospholipid Receptors] [Sphingosine-1-phosphate] [GPR3, GPR6, GPR12] [GPR63]

S1P1: ???; S1P2: ???; S1P3: 9q22.1-q22.2; S1P4: 19p13.3; S1P5: Chr.19; GPR3: 1p36.1-p34.3; GPR6: 6q21-q22.1; GPR12: 13q12; GPR63: 6q16.1-q16.3

*Steroids: estradiol, aldosterone, dihydrotestosterone (DHT), testosterone, dehydroepiandrosterone (DHEA),
dehydroepiandrosterone sulfate (DHEA-S), androstenedione, 5-pregnen-3 alpha-ol-20-one sulphate (pregnenolone sulfate); progesterone; 3a-hydroxy-4-pregnen-20-one (3alphaHP); 5 alpha-pregnan-3 alpha-ol-20-one [aka allopregnanolone]; 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha THP); 5alpha-pregnane-3,20-dione (5alpha-DHP) [aka 5alphaP]; 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-THDOC); 5beta-tetrahydrodeoxycorticosterone (5beta-THDOC); 5-alpha-dihydro-11-deoxycorticosterone (5alpha-DHDOC); etc. [Please note that this list is not comprehensive; it will likely be updated at some point in time.]
Steroid receptors and modulatory sites[Steroid Hormones]
*Substance P (SP), neurokinin A (NKA) [aka substance K or neuromedin L], neurokinin B (NKB) [aka neuromedin K], neuropeptide K, neuropeptide gamma Tachykinin receptors [NK1, NK2, NK3][Tachykinin Peptide Family] [G5] [Putative NK4 receptor] [NK4] [NK4 reappraisal] SP, NKA: 7q21-q22; NKB: 12q13-q21; NK1: Chr.2; NK2: 10q11-q21; NK3: ???
Thromboxane A2 (TxA2)Thromboxane A2 receptors [TP][Prostanoids] [Prostanoid receptors]TP: 19p13.3
Triiodothyronine (T3), Thyroxine (T4)Thyroid hormone receptors [TRalpha isoforms, TRbeta isoforms][Thyroid hormones] [Two novel TRbeta isoforms]TRalpha: 17q11.2; TRbeta: 3p24.3
Thyrotropin-releasing hormone (TRH) Thyrotropin-releasing hormone receptors [TRH-R1, TRH-R2] [TRH-R1, TRH-R2] [TRH-R2 expression in the rat CNS]TRH: 3q13.3-q21; TRH-R1: 8q23
Thyroid-stimulating hormone (TSH) [aka thyrotropin]Thyroid-stimulating hormone receptors [TSHR][TSH] [TSHR] TSH: 1p13; TSHR: 14q31
Trace amines: p-tyramine, beta-phenethylamine, tryptamine, octopamineTrace amine receptors [TAR1][Trace amines] [TAR1]
Urotensin II-related peptide, Urotensin II Urotensin II receptor [UT] (aka GPR14) [Urotensin II] [Urotensin II-related peptide, the endogenous ligand for the urotensin II receptor in the rat brain.] Urotensin II: 1p36; UT: 17q25.3
N-Arachidonoyldopamine (NADA), N-Oleoyldopamine (OLDA), anandamide [aka arachidonoylethanolamide], palmitoylethanolamide and N-acyl ethanolamines [endogenous enhancers of anandamide- mediated VR1 activation], 12- and 15-(S)-hydroperoxyeicosatetraenoic acids, 5- and 15-(S)-hydroxyeicosatetraenoic acids, leukotriene B4Vanilloid VR1 receptors (aka TRPV1 or capsaicin receptors)[Vanilloid receptors] [NADA/OLDA] [Anandamide] [N-acyl ethanolamines] [Lipoxygenase Products]VR1: 17p13
Arginine Vasopressin (AVP) [aka antidiuretic hormone (ADH)] Vasopressin receptors [V1A, V1B, V2][G4]AVP: 20p13; V1A: 12q14-q15; V1B: 1q32; V2: Xq28
Vasoactive intentinal peptide (VIP) VPAC receptors [VPAC1, VPAC2] [VIP/PACAP] [PACAP/Glucagon superfamily] [G4]VIP: 6q26-q27; VPAC1: 3p22; VPAC2: 7q36.3


Neuroactive signaling molecules: gases

Endogenous Ligands








Nitric oxide (NO) soluble guanylate cyclase (sGC), NO receptors [putative NOA, NOB receptors][Nitric Oxide] [sGC] [NOA, NOB] [G4] [NO as a signalling molecule in the nervous system]
Carbon monoxide (CO) soluble guanylate cyclase (sGC) [CO] [G4]


Endogenous neuroactive extracellular signal transducers with putative or unknown binding sites

Endogenous Ligands








Cocaine- and amphetamine-regulated transcript (CART), CART- derived peptidesCART receptors [putative][CART regulates mu opioid and serotonin 5-HT2A receptors] [CART and central dopamine neurons]???
TRH-potentiating peptide [aka Ps4 or Prepro-TRH-(160-169)]TRH-potentiating peptide (Ps4) receptors [putative][Ps4] [Ps4 binding in the rat pituitary] [Ps4] [pro-TRH-Derived Peptides] 3q13.3-q21
SecretoneurinSecretoneurin receptors [putative][Secretoneurin] [Secretoneurin and cerebellar granule cells]
Stanniocalcin 1 (STC1) [also an inhibitor of L-type calcium channels]Stanniocalcin 1 receptors [putative][Stanniocalcin 1 receptors] [Stanniocalcin] [STC1 and L-type calcium channels]8p21-p11.2
beta-Lipotropin, gamma-lipotropinUnknown binding sites[beta-lipotropin may act at MC2 receptors (ACTH receptors] [beta-lipotropin and MC2 receptors in murine adipose tissues]2p23.3
Corticotropin-like intermediate lobe peptide (CLIP)Unknown binding sites[CLIP in the rat dorsal raphe nucleus]2p23.3
Delta sleep-inducing peptide (DSIP)Unknown binding sites["DSIP is influenced by the initiation of sleep"]
EnterostatinUnknown binding sites[Enterostatin] [Enterostatin receptors]
GlicentinUnknown binding sites [Glicentin]
Lipoxin B4 (LXB4)Unknown binding sites[Leukotriene and Lipoxin Receptors] [LXB4 and Sleep]
NocistatinUnknown binding sites[Nocistatin] [Nocistatin] 8p21
Prepro-TRH-(178-199) [aka Ps5]Unknown binding sites[pro-TRH-Derived Peptides]3q13.3-q21
Tyr-MIF-1, Tyr-W-MIF-1, Tyr-K-MIF-1, MIF-1 [some of these peptides may modulate mu opioid and/or GABA-A receptors]Unknown binding sites[Tyr-MIF-1 family peptides]
WE-14WE-14 receptors [putative][WE-14] [WE-14 expression]


Endogenous substances that may or may not be defined as neuroactive extracellular signal transducers:

Endogenous Ligands








Medium and long chain fatty acids: docosahexaenoic acid (DHA), palmitate, oleate, stearate, linoleate, linolenate, etc. [See links for larger lists of ligands. Note that not all of the fatty acids listed are likely to act as extracellular signal transducers in the brain; DHA represents the most likely fatty acid to act extracellularly in the brain.]GPR40 receptors[GPR40] [GPR40] GPR40: 19q13.1
UDP-glucose, UDP-galactose, UDP-glucuronic acid, UDP-N-acetylglucosamineP2Y14 receptors [KIAA0001 ligands] [KIAA0001 renamed P2Y14] [UDP-glucose as an extracellular signaling molecule]
Agouti signaling protein (ASP) [an endogenous antagonist]Melanocortin MC1, MC4 receptors[ASP and MC1, MC4]ASP: 20q11.2
beta-LactotensinNeurotensin NT2 receptors[beta-Lactotensin and NT2 receptors] [NT2 receptors in the rat brain] [Neurotensin exhibits antagonist activity at NT2 receptors in CHO cells]
Peroxisome proliferatorsPeroxisome proliferator activated receptors [PPARs]
ProctolinProctolin receptors [putative][Proctolin in the human brain stem]
Prokineticin 2beta, prokineticin 1, prokineticin 2 Prokineticin PK1 receptors [Molecular cloning and characterization of prokineticin receptors.] [Identification and Pharmacological Characterization of Prokineticin 2{beta} as a Selective Ligand for Prokineticin Receptor 1.] 2p13.1
Peptide P518 SP9155 (aka AQ27 and GPR103) receptors[Peptide P518 and SP9155]
Apolipoprotein AIV Unknown binding sites

[Apolipoprotein IV and rat hypothalamus] [Apolipoprotein IV binding]

C-peptideUnknown binding sites[C-peptide binding]11p15.5
CarnosineUnknown binding sites, ryanodine receptors[Carnosine and ryanodine receptors]
Chromogranin A (CgA) derived peptides: vasostatin I, vasostatin II, parastatin, chromostatin, beta-granin, etc. Unknown binding sites[Chromogranin A] 14q32
Chromogranin B (CgB) derived peptides: PE-11, WE-15, GAWK, CCB, SR-17, HQ-34, etc.Unknown binding sites

[PE-11] [GAWK/CCB] [SR-17/HQ-34] [Chromogranin B derived peptides] [CgB derived peptides]

GAIPIRRHUnknown binding sites[GAIPIRRH]20q13.2
Miniglucagon (glucagon 19-29)Unknown binding sites[Miniglucagon]
Prepro-TRH derived peptides: Prepro-TRH-(53-74), Prepro-TRH-(178-185), Prepro-TRH-(186-199), Prepro-TRH-(83-106), Prepro-TRH-(208-255) Unknown binding sites[pro-TRH-Derived Peptides]3q13.3-q21
RFamide-related peptide-2 (RFRP-2)Unknown binding sites[RFRP-2]
Stanniocalcin 2 (STC2)Unknown binding sites[Stanniocalcin 2] ???
TRH-like peptides: pGlu-Glu-Pro-NH(2) (EEP), pGlu-Val-Pro-NH(2) (Val(2)-TRH), Leu(2)-TRH, Phe(2)-TRH, Tyr(2)-TRH, TRH-Gly [the immediate precursor of TRH]Unknown binding sites [TRH-like peptides] [TRH-like peptides and cocaine]
TRH metabolites: Cyclo(His-Pro), TRH-OHUnknown binding sites[Cyclo(His-Pro)] [TRH-OH] 3q13.3-q21

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