DISTRIBUTION OF 7 MAJOR NEUROTRANSMITTER RECEPTORS IN THE STRIATE CORTEX OF THE NEW-WORLD MONKEY CALLITHRIX-JACCHUS

The distribution of seven different binding sites for the transmitters L-glutamate (L-glutamate binding sites and N-methyl-D-aspartate recep tor), GABA (GABA(A) receptor), noradrenaline (alpha1 receptor), acetyl choline (muscarinic M1 and M2 receptors) and serotonin (5-hydroxytrypt amine1 receptor) are analysed in the primary visual cortex (area 17) o f the common marmoset, Callithrix jacchus, using quantitative autoradi ography. All binding sites show a well-defined laminar pattern, which changes sharply at the cytoarchitectonic border to area 18. The quanti tative data show that the distribution of different receptors is relat ively invariant across the cortical layers. Almost all receptors show a maximum in supragranular layers, low densities in layers IVA/IVB and a second maximum in layer IVC. Statistical analysis of these similari ties in laminar distribution patterns of different receptors (co-distr ibution) reveals, as in other brain regions and species, that L-glutam ate binding sites are co-distributed with N-methyl-D-aspartate, GABA(A ), and muscarinic M1 and M2 receptors. This may reflect the structural basis of a possible interaction between these receptors and their res pective transmitters on the level of single cortical layers. Further c o-distributions are found between N-methyl-D-aspartate, GABA(A) and M1 , as well as between alpha1 and M1 and finally between M1 and M2 recep tors. Since not all receptors are co-distributed, the similarities in laminar patterns reveal specific aspects of the neurochemical organiza tion of the cortex when receptors of different transmitter systems are analysed in the same brain. A comparison with data from area 17 of hu man, rhesus and other monkeys reveals a very similar distribution patt ern for most of the receptors investigated among the species. This mea ns that not only the cytoarchitectonic structure of the striate cortex , but also the neurochemical organization of this area is highly conse rved during primate evolution.