Regional distribution and cellular localization of 5-HT2C receptor mRNA in monkey brain:: Comparison with [3H]mesulergine binding sites and choline acetyltransferase mRNA

The distribution of serotonin 5-HT2C receptor mRNA in monkey brain was studied by in situ hybridization and compared with the distribution of [H-3]mesulergine binding sites as visualized by receptor autoradiography. 5-HT2C receptor transcripts showed a widespread and heterogeneous distribution. The strongest hybridization signal was detected in choroid plexus. In neocortex, 5-HT2C mRNA was detected in layer V of all cortical regions examined except in the calcarine sulcus, which was devoid of signal. Several structures within the striatum and basal forebrain were strongly labeled: nucleus accumbens, ventral aspects of anterior caudate and putamen, septal nuclei, diagonal band, ventral striatum, and extended amygdala. Several thalamic, midbrain, and brainstem nuclei also contained 5-HT2C mRNA. Comparison of the distributions of 5-HT2C mRNA and specific [H-3]mesulergine binding sites showed a good agreement in the majority of brain regions, suggesting a predominant somatodendritic localization of 5-HT2C receptors. A possible localization to axon terminals of 5-HT2C receptors is suggested by the disagreement observed in some regions such as septal nuclei and horizontal limb of the diagonal band (presence of mRNA with apparent absence of binding sites) and interpeduncular nucleus (presence of binding sites with apparent absence of mRNA). Comparison of 5-HT2C receptor and choline acetyltransferase mRNA distributions indicate that some regions where cholinergic cells are located are also enriched in cells containing 5-HT2C mRNA. Although the present methodology does not allow strict colocalization of both mRNA species to the same cells, the codistribution observed in several regions provides a possible anatomical substrate for the described modulation of acetylcholine release by 5-HT2C receptors. Synapse 42:12-26, 2001. (C) 2001 Wiley-Liss, Inc.