GALANIN-IMMUNOREACTIVE SYNAPTIC TERMINALS ON BASAL FOREBRAIN CHOLINERGIC NEURONS IN THE RAT

Previous studies have indicated that galanin is one of the most abunda nt peptides in the basal forebrain and that it has a significant modul atory influence on cholinergic transmission. The aim of the present st udy was to use a light electron microscopic correlation technique to d etermine whether galanin-immunoreactive terminals form synaptic contac ts with basal forebrain cholinergic cells of the rat. Sections from fi xed-perfused brains were stained at the light and electron microscopic levels for galanin and choline acetyltransferase immunoreactivity in the same section by using a dual-colour immunohistochemical method. Th e results showed that galanin-immunoreactive axonal terminals are unev enly distributed in the medial septal nucleus, the diagonal band, and the nucleus basalis. Galanin-positive synapses were most prominent on choline acetyltransferase-positive neurons in the lateral parts of the nucleus of the diagonal band and in the posterior half of the nucleus basalis, which is where there was the greatest overlap between the di stribution of galanin-immunoreactive terminals and choline acetyltrans ferase-positive neurons. The origins of these galanin-positive termina ls are not known, but the results confirm that the basal forebrain gal aninergic system has a synaptic influence on basal forebrain cholinerg ic neurons in the rat. (C) 1997 Wiley-Liss, Inc.