Distribution of major neurotransmitter receptors in the motor and somatosensory cortex of the rhesus monkey

The in vitro quantitative autoradiographic technique was used to characterize the distributions of α 1 , α 2 , β 1 and β 2 adrenergic, D 1 and D 2 dopaminergic, 5-HT 1 and 5-HT 2 serotonergic, M 1 and M 2 cholinergic, GABA A and benzodiazepine receptors in the motor (Brodmann's area 4) and somatosensory (Brodmann's areas 3, 1 and 2) cortex of the adult rhesus monkey. All receptor subtypes studied were present throughout all layers of both areas. In the somatosensory cortex, each receptor had its own laminar distribution. Some subtypes of the same receptor (5-HT 1 and 5-HT 2; α 1 and α 2 ) had complementary distributions while others (β 1 and β 2; D 1 and D 2; M 1 and M 2) had largely overlapping distributions. In contrast, different receptors had remarkably coincidental distributions in the motor cortex. In this area, they all tended to concentrate in layers I, II and the upper part of layer III. However, such coextensive distribution of many types of neurotransmitter receptors is not observed in motor cortex of rats and humans and therefore may be a distinctive feature of motor cortex in the rhesus monkey. The findings described in this paper indicate that somatosensory and motor areas are distinct in their receptor architecture and that receptor autoradiography provides a useful complement to classical histological techniques in elucidating areal differences in the cortex.