COMPARATIVE ANATOMICAL DISTRIBUTION OF SEROTONIN 1A, 1D-ALPHA AND 2A RECEPTOR MESSENGER-RNAS IN HUMAN BRAIN POSTMORTEM

The distribution of messenger ribonucleic acids (mRNA) for serotonin ( 5-HT) receptors of 1A, 2A and 1D alpha type (5-HT1A, 5-HT2A, and 5-HT1 D alpha) was examined and compared in autoptic human brain by means of in-situ hybridization using cRNA probes, in those areas with the high est density of the receptors, as observed with binding techniques. The results showed that the 5-HT1A receptor mRNA was abundantly expressed in the layers LI-VI of all cortical areas under examination, but the highest expression was found in the hippocampus, particularly in the g ranular cells of the dentate gyrus and in the pyramidal cell layer of the Hammon's horn. The 5-HT2A receptor mRNA was mainly present in the layers III-V of the cortex, with regional differences which were parti cularly marked in the striate area where the layer IV was specifically labeled. On the other hand, in the hippocampus, 5-HT2A receptor mRNA was restricted to the pyramidal cell layer of the CA1 field of the Ham mon's horn. No expression of both 5-HT2A and 5-HT1D alpha receptors wa s detected in the caudate nucleus and in putamen where only a light la beling by means of the 5-HT1A receptor probe was detected. The 5-HT1D alpha receptor mRNA was found only in the CA3 field of the Hammon's ho rn. These findings confirm that 5-HT receptors are widely distributed in the brain, but that the different subtypes possess a selective loca lization in different neuronal populations which, in turn, may express one or more receptors. The regional differences may represent the ana tomical substrate of different serotonergic functions and dysfunctions .