A neuropeptide is an endogenous protein molecule comprised of at least two amino acids, which are chained together by peptide bonds. They are found in large dense-core vesicles on nearly all areas of the neuron, most commonly the axon terminal at the synapse. Approximately 100 different neuropeptides have been identified.

The function of a neuropeptide often determines its classification as a neurotransmitter or hormone, but the terms are frequently intermixed. Generally, neuropeptides exert more prolonged and diverse effects on behavior than neurotransmitters, and act directly at G-coupled protein and metabotropic receptor sites. 

Many populations of neurons have distinctive biochemical phenotypes. For example, in one subpopulation of about 3000 neurons in the arcuate nucleus of the hypothalamus, three anorectic peptides are co-expressed: α-melanocyte-stimulating hormone (α-MSH), galanin-like peptide, and cocaine-and-amphetamine-regulated transcript (CART), and in another subpopulation two orexigenic peptides are co-expressed, neuropeptide Y and agouti-related peptide (AGRP). These are not the only peptides in the arcuate nucleus; β-endorphin, dynorphin, enkephalin, galanin, ghrelin, growth-hormone releasing hormone, neurotensin, neuromedin U, and somatostatin are also expressed in subpopulations of arcuate neurons. These peptides are all released centrally and act on other neurons at specific receptors. The neuropeptide Y neurons also make the classical inhibitory neurotransmitter GABA.

Invertebrates also have many neuropeptides. CCAP has several functions including regulating heart rate, allatostatin and proctolin regulate food intake and growth, bursicon controls tanning of the cuticle and corazonin has a role in cuticle pigmentation and moulting.

Cat#Product Name
300038Crayfish RFamide 1 / Neuropeptide DF2 (DRNFLRF-amide), an FMRFamide
300191H-Gly-Gly-Gly-OH, Neuropeptide-like peptide, NLP-32-3
300284FMRFamide-like neuropeptide, AF1
300455A-18-F-NH2; Morphine Modulating Neuropeptide
300588(Pro34)-Neuropeptide Y (porcine)
301157Neuropeptide EI-Gly-Arg-Arg-MCH (human, mouse, rat)
301277Neuropeptide Y (2-36) (porcine)
301488Pheromonotropin (Pseudaletia separata), Pheromonotropic neuropeptide
301496Neuropeptide W-23 (rat)
301525Neuropeptide Y (22-36)
301696Octa-neuropeptide, Octapeptide OP
302346Neuropeptide AF (hNPAF), Human /Neuropeptide A-18-F/NPAF
302992Neuropeptide Y-Lys(Biotin), human, rat; NPY-Lys(Biotin), human, rat
303424Pheromone Biosynthesis Activating Neuropeptide
303465FMRF-like Neuropeptide; SchistoFLRFamide
303627Neuropeptide Y (18-36)
303654LWamide neuropeptide II, He-LWamide II
303757Neuropeptide W-30 (human)
303951Galanin (1-13)-Neuropeptide Y (25-36) amide
303984(Leu31,Pro34)-Neuropeptide Y (human, rat)
304903Neuropeptide-glutamic acid-isoleucine, Neuropeptide EI (human, mouse, rat)
305200Neuropeptide K
305624[S1]-Mollusca neuropeptide, FMRF-related peptide, SDPFLRF-NH2
305706Neuropeptide Y (free acid) (human, rat)
305765Neuropeptide S (1-10) (human)
306416Neuropeptide GE (Glycine-Glutamic acid)
306938Neuropeptide RFRP-2
307359Neuropeptide VF (56-92) (human), RFRP-1
307563Neuropeptide Y / Melanostatin, frog
307572Neuropeptide F
308212Neuropeptide W-30 (rat)
308648(His32,Leu34)-Neuropeptide Y (32-36)
309169Neuropeptide 26RFa, Hypothalamic Peptide, frog
309402Neuropeptide SF (human)
309441[Thr30]-Neuropeptide Y, human
309624Neuropeptide Y (13-36) (human, rat)
310317Neuropeptide VF (124-131) (human)
310965Orphan GPCR SP9155 Agonist P518, Neuropeptide 26RFa, Hypothalamic Peptide
310966Neuropeptide FF (5-8)/Morphine Modulating Peptide, C-Terminal Fragment
311531Neuropeptide Y (3-36) (porcine)
311598Neuropeptide Y
312151Neuropeptide S (human)
312438Bradykinin-Like Neuropeptide (Aplysia californica)
312508(Pro30,Tyr32,Leu34)-Neuropeptide Y (28-36)
312998Neuropeptide Y (1-24) amide (human, rat)
313085[Pro34]-Neuropeptide Y, human, rat; [Pro34]-NPY, human, rat
313806H-Gly-Trp-Gly-OH, Neuropeptide-like peptide, NLP-32-9
313810(Leu31,Pro34)-Neuropeptide Y (13-36) (human, rat)
313977(Des-Bromo)-Neuropeptide B (1-23) (human)
314349H-Gly-Gly-Gly-Gly-OH, Neuropeptide-like peptide, NLP-32-7
314408Neuropeptide Y (3-36) (human, rat)
314522Neuropeptide FF Morphine Modulating Neuropeptide F-8-F/NPFF
314580Orphan GPCR SP9155 Agonist P550/Neuropeptide 26RFa/Hypothalamic Peptide
314639Neuropeptide Y (13-36) (porcine)
314925Neuropeptide Y
315357Bradykinin-Like Neuropeptide (3-11) (Aplysia californica)
315381Neuropeptide Y (2-36) (human, rat)
315535Neuropeptide S (rat)
316044(Leu31,Pro34)-Neuropeptide Y (porcine)
318153neuropeptide NAP