Galanin

Galanin is a 29-amino acid neuropeptide (30 AA in humans) widely distributed in the central and peripheral nervous system and GI tract. It is one of the most multifunctional neuropeptides known, modulating pain processing, cognition, mood, feeding, pancreatic insulin release, and cardiovascular function. Galanin overexpression has been documented in Alzheimer's disease brains, generating sustained research interest in galanin receptor subtypes as therapeutic targets.

Galanin acts through three G protein-coupled receptors: GalR1, GalR2, and GalR3. GalR1 and GalR3 couple to Gi/o, reducing cAMP and inhibiting neuronal firing. GalR2 couples to Gq/11, activating phospholipase C and increasing intracellular calcium. In the spinal cord dorsal horn, galanin co-released with substance P inhibits nociceptive transmission via GalR1. In Alzheimer's disease, galanin hyperinnervation of surviving cholinergic neurons in the basal forebrain is proposed to inhibit acetylcholine release, potentially contributing to cognitive decline. GalR2 may alternatively exert neuroprotective effects.

Alzheimer's disease research drives much of the current galanin field. Postmortem brains of AD patients show up to 200% increases in galanin expression and receptor density in basal forebrain regions. Selective GalR1/GalR3 antagonists and GalR2 agonists are under preclinical investigation for AD and mood disorders. Galanin also modulates insulin secretion from pancreatic islets, making it relevant to diabetes research. Pain models show a dual role: pro-nociceptive at supraspinal sites and anti-nociceptive spinally. No galanin-targeting drug has reached clinical approval.