Mapping of 5-HT2A receptors and their mRNA in monkey brain: [H-3]MDL100,907 autoradiography and in situ hybridization studies

The anatomic distribution of serotonin 5-HT2A receptors visualized with [H- 3]MDL100,907 and of their mRNA detected by in situ hybridization were studi ed in monkey brain. Both autoradiographic patterns of signal showed heterog eneous distributions and were in general in good agreement in the majority of brain regions. In most neocortical areas, [H-3]MDL100,907 presented a fo ur-banded pattern with layers I and III-IV more intensely labeled and layer s II and V-VI showing weaker labeling. 5-HT2A receptor mRNA was detected in layers III and IV, and in some cases also in layers II and V. In intra- an d extra-calcarine areas of striate cortex a five-banded pattern was disting uished, with layers III and IVc-V showing the highest densities of [H-3]MDL 100,907 labeling. These two areas showed the highest neocortical hybridizat ion signal. An unexpected finding was the presence of low densities of [H-3 ]MDL100,907 labeling and 5-HT2A receptor mRNA in choroid plexus. Comparison of the distribution of [H-3]1MDL100,907 and [H-3]ketanserin binding sites in monkey brain regions with high nonspecific [H-3]ketanserin binding (caud ate, putamen, substantia nigra, inferior olive) revealed specific binding o f [H-3]MDL100,907 with very low nonspecific binding. Some differences were noted between the distribution of [H-3]MDL100,907-labeled 5-HT2A receptors in monkey brain and the previously reported distribution of these receptors in human brain: absence of striosome labeling in monkey striatum and diffe rent patterns of neocortical labeling. The present results provide the firs t detailed comparison of 5-HT2A receptor and mRNA distribution in primate b rain. The observed species differences in 5-HT2A receptor distribution shou ld be considered when extrapolating results among different species. J. Com p. Neurol. 429:571-589, 2001. (C) zool Wiley-Liss, Inc.