Galanin receptors: involvement in feeding, pain, depression and Alzheimer's disease.

Galanin, a neuroendocrine peptide with a multitude of functions, binds to and acts on specific G-protein coupled receptors. Only one galanin receptor subtype, GalRI, has been cloned so far, although pharmacological evidence suggests the presence of more than one galanin receptor subtype. These receptors mediate via different Gi/Go-proteins the inhibition of adenylyl cyclase, opening of K+-channels and closure of Ca2+-channels. Galanin inhibits secretion of insulin, acetylcholine, serotonin and noradrenaline, while it stimulates prolactin and growth hormone release. Determination of structural components of galanin receptors required for binding of the peptide ligand as carried out recently will facilitate the screening and design of molecules specifically acting on galaninergic systems with therapeutic potential in Alzheimer's disease, feeding disorders, pain and depression.