Neuropeptide

A neuropeptide is a short peptide synthesized by a neuron and used as a signaling molecule in the central or peripheral nervous system. Unlike classical neurotransmitters (glutamate, GABA, dopamine) which act on a millisecond timescale through ion channels, neuropeptides modulate synaptic communication on longer time constants (seconds to minutes) by activating G protein-coupled receptors (GPCRs) located at some distance from the release site. They therefore act as neuromodulators rather than strict neurotransmitters.

Neuropeptide biosynthesis starts with translation of a large pre-pro-peptide, which is cleaved in the endoplasmic reticulum and then in secretory vesicles by prohormone convertases (PC1/PC3, PC2). A single pro-protein often yields several bioactive peptides: proopiomelanocortin (POMC) for instance gives rise to ACTH, α-MSH, β-endorphin, and other fragments, each with its own target receptor.

Major classes include endogenous opioids (endorphins, enkephalins, dynorphins, involved in nociception and reward), orexigenic/anorexigenic neuropeptides (NPY, AgRP versus α-MSH and CART, which regulate appetite at the hypothalamic level), stress peptides (CRH, urocortins), sleep and circadian peptides (orexins/hypocretins, VIP), and hypothalamic releasing or inhibiting hormones acting on the pituitary (GHRH, somatostatin, TRH, GnRH).

Their research relevance is substantial: they are pharmacological targets in chronic pain, obesity, mood disorders, addiction, and neurodegenerative diseases. Synthetic peptide analogs allow researchers to dissect, in vitro and in vivo, receptor subtype selectivity, functional bias (β-arrestin versus G-protein agonism), and behavioral effects in animal models.

Neuropeptides differ from classical neurotransmitters (glutamate, GABA, dopamine) by their synthesis mode (pre-pro protein precursor, post-translational enzymatic cleavage by prohormone convertases PC1/PC2), storage (large dense-core vesicles LDCV) and release (co-release with a classical transmitter upon high-frequency activation). Their volumetric rather than synaptic diffusion gives them wider spatial range and longer action duration (seconds to minutes).

Major neuropeptide families include: pro-opiomelanocortin (POMC) family — β-endorphin, α-MSH, ACTH; enkephalin/dynorphin family — Met-enkephalin, Leu-enkephalin, dynorphins; tachykinin family — substance P, neurokinins; somatostatin/cortistatin family; VIP/PACAP/glucagon family; hypocretin/orexin family regulating arousal and appetite; neuropeptide Y and related (NPY, PYY, PP). In rodent preclinical research, neuropeptidic tools include Semax (ACTH(4-10) derivative), Selank (tuftsin derivative), Dihexa (angiotensin IV peptidomimetic), DSIP (Delta-sleep inducing peptide) — Semax, Selank and DSIP are available from Atlas Lab Solutions for studies of cognition, sleep and neuroplastic processes.