REGIONAL AND CELLULAR EXPRESSION SITES OF THE ALPHA(1) SUBUNIT OF GABA(A) RECEPTORS IN THE RAT BASAL FOREBRAIN - A CYTOCHEMICAL STUDY WITH GLUTAMIC-ACID DECARBOXYLASE, CHOLINE-ACETYLTRANSFERASE, CALCIUM-BINDING PROTEINS AND NITRIC-OXIDE SYNTHASE AS 2ND MARKERS

Forebrain sections of adult male Wistar rats were processed for the im munohistochemical detection of the GABA(A) receptor alpha(1) subunit. Alternate sections were used for double-staining with antibodies to gl utamic acid decarboxylase (GAD), choline acetyltransferase (ChAT), the calcium binding proteins parvalbumin (PARV), calbindin (CALB) and cal retinin (CR) as well as to nitric oxide synthase (NOS). alpha(1) recep tor subunit-immunoreactive neurons were found to be inhomogeneously di stributed in the rat basal forebrain. Numerous alpha(1) subunit-immuno stained neurons occupied the central part of medial septum and diagona l band, the whole ventral pallidum and the globus pallidus. A moderate number was found in the lateral septum, and only very few in the stri atum and nucleus accumbens. Double-immunofluorescence labelling reveal ed an apparently complete co-expression of GAD-immunoreactivity in alp ha(1) subunit-immunoreactive cells of rat basal forebrain, but only a region-dependent proportion of GAD-immunoreactive cells showed alpha(1 ) subunit-immunoreactivity. Co-expression of PARV-immunoreactivity cha racterized the vast majority of the alpha(1) subunit-immunoreactive ce lls in the medial septum, diagonal band, ventral pallidum and globus p allidus. Striatal alpha(1) subunit-immunopositive neurons appeared PAR V-immunonegative and did also not react with the other immunoreagents used in this study, except the GAD-antibody. CR-immunoreactivity was c o-expressed in alpha(1) subunit-immunopositive cells of the ventral la teral septal nucleus and only exceptionally in the ventral pallidum, w here the vast majority of GR-positive cells was monolabelled. A small minority of ChAT-immunoreactive, but in no case CALB- and NOS-immunore active cells were found to express the alpha(1) subunit-immunoreactivi ty. These findings confirm the data obtained by analyses of other brai n regions suggesting a preferred co-existence of this GABA(A) receptor subunit with PARV and to a lesser degree with CR.