Neuropeptides

Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the gut, muscles, and heart.

There are over 100 known neuropeptides, representing the largest and most diverse class of signaling molecules in the nervous system. Neuropeptides are synthesized from large precursor proteins which are cleaved and post-translationally processed then packaged into dense core vesicles. Neuropeptides are often co-released with other neuropeptides and neurotransmitters in a single neuron, yielding a multitude of effects. Once released, neuropeptides can diffuse widely to affect a broad range of targets.

Neuropeptides are often co-released with other neurotransmitters and neuropeptides to modulate synaptic activity. Norepinephrine (noradrenaline). In neurons of the A2 cell group in the nucleus of the solitary tract), norepinephrine co-exists with neuropeptides galanin, enkephalin, neuropeptide Y.

Oxytocin (from PDB entry 7otd) and vasopressin (from PDB entry 7bb7) have striking and specific effects on social behaviours, including maternal behaviour and pair bonding.

Depending on the species, oxytocin receptor-expressing cells are located in other areas, including the amygdala and bed nucleus of the stria terminalis.

In the pituitary gland, oxytocin is packaged in large, dense-core vesicles, where it is bound to neurophysin I as shown in the inset of the figure; neurophysin is a large peptide fragment of the larger precursor protein molecule from which oxytocin is derived by enzymatic cleavage.