Quantitative auto radiography of 11 different transmitter binding sites in the basal forebrain region of the rat—Evidence of heterogeneity in distribution patterns

Abstract

The distribution of 12 different binding sites for acetylcholine, l-glutamate, GABA, 5-hydroxytryptamine, dopamine and noradrenaline was measured with quantitative receptor autoradiography in four regions of the rat basal forebrain (medial septal nucleus including vertical and horizontal limbs of the diagonal band of Broca, magnocellular preoptic nucleus, substantia innominata and basal nucleus of Meynert, ventral pallidum). l-Glutamate binding sites represent the largest portion of the analysed receptors in all regions, followed by muscarinic 2, 5-hydroxytryptamine, and GABA A receptors. Muscarinic 1, dopamine 1, dopamine 2 and 5-hydroxytryptamine 2 receptors and α 1-, α 1A- and α 1B-adrenoceptors represent the minor receptor populations. The largest portion of the dopamine receptors is represented by the dopamine, subtype, and the α 1B subtype dominates the α 1-adrenoceptor group. A heterogeneity of the distribution patterns of the different receptors throughout the basal forebrain regions is found. A comparison of the patterns shows that α 1-adrenoceptors have a similar regional distribution to that of the muscarinic, receptors, but both receptor types have reciprocal distributions compared with the 5-hydroxytryptamine 1 receptors. The results indicate that one transmitter may exert different effects in the basal forebrain regions depending on the densities of the respective receptor subtypes. Moreover, similar or reciprocal distribution patterns of some, but not all, analysed receptors point to a non-random association (co-distribution) of the different transmitter systems in the basal forebrain regions.