SEROTONIN(1A) RECEPTORS ARE EXPRESSED BY A SUBPOPULATION OF CHOLINERGIC NEURONS IN THE RAT MEDIAL SEPTUM AND DIAGONAL BAND OF BROCA - A DOUBLE IMMUNOCYTOCHEMICAL STUDY

The possible colocalization of 5-hydroxytryptamine(1A) receptors and c holine acetyltransferase in the same neurons of the medial septum and diagonal band of Broca was investigated using double immunocytochemica l techniques, either on the same section or on adjacent thin sections of the rat brain. The presence of both antigens in the same neurons wa s demonstrated at the light and electron microscopic levels. The propo rtion of cholinergic neurons that express 5-hydroxytryptamine(1A) rece ptors was similar in the different parts of the septal complex (around 25%). By contrast, the proportion of 5-hydroxytryptamine(1A) receptor -positive neurons also exhibiting choline acetyltransferase immunoreac tivity was much higher (40-44%) in the dorsal and ventral groups of ch olinergic cells, than in the intermediate group (18%). In line with th e topographical distribution of cholinergic projections, this result p oints out the potential involvement of 5-hydroxytryptamine(1A) recepto rs in the control of the septohippocampal cholinergic projection by se rotonin. This connection might be relevant to learning and memory, and in the appearance of age-dependent or neurodegenerative cognitive def icits, which have been shown to involve alterations in both the seroto ninergic and the cholinergic systems. Copyright (C) 1996 Published by Elsevier Science Ltd.