QUANTITATIVE RECEPTOR AUTORADIOGRAPHY OF 8 DIFFERENT TRANSMITTER-BINDING SITES IN THE HIPPOCAMPUS OF THE COMMON MARMOSET, CALLITHRIX-JACCHUS

The regional and laminar distributions of eight different transmitter- binding sites were measured in the marmoset hippocampus by means of qu antitative in vitro receptor autoradiography. Receptors for 5-HT1, L-g lutamate, N-methyl-D-aspartate (NMDA) and GABA(A) were similarly distr ibuted. The highest concentrations of these receptors were found in th e pyramidal layer of CA1 and the molecular layer of the dentate gyrus. The 5-HT2 receptors showed the highest concentrations in the oriens l ayer of CA2. The highest concentrations of muscarinic M1 receptors wer e seen in the pyramidal layer of CA1. Muscarinic M2 receptors were mos t densely concentrated in the pyramidal layers of CA1, CA2 and CA3. Th e noradrenergic alpha(1) receptors were most densely packed in the rad iatum-lacunosum-molecular layer of CA2 and the molecular layer of the dentate gyrus. Statistically significant co-distributions of serotonin ergic, glutamatergic and GABAergic receptors point to possible interac tions between these receptor systems in the same hippocampal regions a nd layers. Comparisons of marmoset distribution patterns for GABA(A), NMDA, L-glutamate and 5-HT1 receptors with those in human hippocampi a nd those of other primates showed similarities between them. Clear dif ferences in the patterns of alpha(1) M1, M2 and 5-HT2 receptors could be seen between marmoset and human hippocampi, indicating a high degre e of species specificity in a presumably ''conservative'' brain region . More similarities, however, could be found between marmoset and huma n hippocampi than between those of rat and human brains, especially in relation to 5-HT1 and GABA(A) receptors and L-glutamate-binding sites . In addition to the functional significance of receptor distribution patterns, such studies represent a valuable tool for the analysis of n eurochemical aspects of brain evolution.