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

The distribution of serotonin 5-HT2C receptor mRNA in monkey brain was stud ied by in situ hybridization and compared with the distribution of [H-3]mes ulergine binding sites as visualized by receptor autoradiography. 5-HT2C re ceptor 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 exce pt in the calcarine sulcus, which was devoid of signal. Several structures within the striatum and basal forebrain were strongly labeled: nucleus accu mbens, ventral aspects of anterior caudate and putamen, septal nuclei, diag onal band, ventral striatum, and extended amygdala. Several thalamic, midbr ain, and brainstem nuclei also contained 5-HT2C mRNA. Comparison of the dis tributions of 5-HT2C mRNA and specific [H-3]mesulergine binding sites showe d a good agreement in the majority of brain regions, suggesting a predomina nt somatodendritic localization of 5-HT2C receptors. A possible localizatio n to axon terminals of 5-HT2C receptors is suggested by the disagreement ob served in some regions such as septal nuclei and horizontal limb of the dia gonal band (presence of mRNA with apparent absence of binding sites) and in terpeduncular nucleus (presence of binding sites with apparent absence of m RNA). Comparison of 5-HT2C receptor and choline acetyltransferase mRNA dist ributions indicate that some regions where cholinergic cells are located ar e also enriched in cells containing 5-HT2C mRNA. Although the present metho dology does not allow strict colocalization of both mRNA species to the sam e 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.