PARCELLATION OF THE FRONTAL-CORTEX OF THE NEW-WORLD MONKEY CALLITHRIX-JACCHUS BY 8 NEUROTRANSMITTER-BINDING SITES

The most extensive development during primate brain evolution involves the cortex of the frontal lobe, especially its prefrontal region. The distribution of neurotransmitter receptors is unknown in this part of the cortex of New World monkeys. The respective distributions of eigh t different receptors for the transmitters L-glutamate (L-glu and NMDA ), gamma-amino-butyric acid (GABA(A)), noradrenaline (alpha(1)), acety lcholine (M(1) and M(2)) and serotonin (5-HT1 and 5-HT2) were therefor e studied in cortical areas of the frontal lobe of the lissencephalic New World monkey, Callithrix jacchus. The results are compared to earl ier data on Old World monkeys in order to obtain insight into evolutio nary trends at the level of chemical neuroanatomy. Our results indicat e that the density and laminar pattern of some receptors change precis ely at the cytoarchitectonic boundaries between different cortical are as, while some other receptors do not exhibit measurable changes. For example, the premotor area 6 can be distinguished from prefrontal area s by its high concentration of adrenergic al receptors as labelled wit h [H-3] prazosin, with only the cingulate area 24 showing higher value s. In other cases, the receptor distribution changes within a cytoarch itectonically homogeneous area. Thus, area 8 can be subdivided into do rsal and Ventral regions on the basis of the distribution of GABA,, mu scarinic and serotonin receptors. Comparison of these results in a New World monkey with receptor distributions in other primate species rev eals much larger interspecies differences in the areas of the frontal lobe than e.g. in the primary visual cortex. This is interpreted as an indication of extensive changes in the neurochemical organisation of this part of the brain during primate brain evolution.