Distribution of seven major neurotransmitter receptors in the striate cortex of the new world monkey callithrix jacchus

Abstract

The distribution of seven different binding sites for the transmitters l-glutamate ( l-glutamate binding sites and N-methyl- d-aspartate receptor), GABA (GABA A receptor), noradrenaline (α 1 receptor), acetylcholine (muscarinic M 1 and M 2 receptors) and serotonin (5-hydroxytryptamine 1 receptor) are analysed in the primary visual cortex (area 17) of the common marmoset, Callithrix jacchus, using quantitative autoradiography. All binding sites show a well-defined laminar pattern, which changes sharply at the cytoarchitectonic border to area 18. The quantitative data show that the distribution of different receptors is relatively 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 similarities in laminar distribution patterns of different receptors (co-distribution) reveals, as in other brain regions and species, that l-glutamate binding sites are co-distributed with N-methyl- d-aspartate, GABA A, and muscarinic M 1 and M 2 receptors. This may reflect the structural basis of a possible interaction between these receptors and their respective transmitters on the level of single cortical layers. Further co-distributions are found between N-methyl- d-aspartate, GABA A and M 1, as well as between α 1 and M 1 and finally between M 1 and M 2 receptors. Since not all receptors are co-distributed, the similarities in laminar patterns reveal specific aspects of the neurochemical organization of the cortex when receptors of different transmitter systems are analysed in the same brain. A comparison with data from area 17 of human, rhesus and other monkeys reveals a very similar distribution pattern for most of the receptors investigated among the species. This means that not only the cytoarchitectonic structure of the striate cortex, but also the neurochemical organization of this area is highly conserved during primate evolution.