Quantitative autoradiographic mapping of serotonin 5‐HT 1 and 5‐HT 2 receptors and uptake sites in the neocortex of the rhesus monkey

The in vitro autoradiographic technique was used to characterize the distribution of serotonin 5‐HT 1 and 5‐HT 2 receptors and uptake sites in 11 cortical areas of frontal, parietal, and occipital lobes in the rhesus monkey; 5‐HT 1 receptors were labeled with [ 3 H]5‐HT; 5‐HT 2 receptors were labeled with [ 3 H]ketanserin; and 5‐HT uptake sites were labeled with [ 3 H]citalopram. Five‐HT 1 and 5‐HT 2 receptors and 5‐HT uptake sites were found in every cortical area examined with the absolute concentration of 5‐HT 1 receptors higher than that of 5‐HT 2 receptors in all areas. In eight regions of prefrontal and parietal as well as in prestriate cortex, 5‐HT 1 and 5‐HT 2 receptors had complementary distribution profiles: 5‐HT 1 receptors were concentrated in layers I and II and the upper strata of layer III, while 5‐HT 2 receptors had their highest concentration throughout layers III and IV. Only the primary motor and visual cortex had receptor distributions different from that described above. Thus, in the primary visual cortex, both 5‐HT 1 and 5‐HT 2 receptors were found in high concentration in sublayer IVcß, though the density of 5‐HT 1 receptor was also high in other subdivisions of layer IV and in layers III, V, and VI. In the primary motor cortex, both receptor subtypes were concentrated in layers I and II and the upper strata of layer III. The pattern of distribution of serotonin uptake sites did not match the patterns of distribution of either 5‐HT 1 or 5‐HT 2 receptors alone; rather it approximated the combined patterns of distribution of both receptor subtypes. The complementary patterns of distribution of 5‐HT 1 and 5‐HT 2 receptors in most areas of the monkey cerebral cortex suggest that these two receptor subtypes may make differential contributions to cortical functions.