5-HT1A and 5-HT2A receptor mRNAs and binding site densities are differentially altered in schizophrenia

We have investigated 5-HT1A (serotonin1A) and 5-HT2A (serotonin2A) receptor mRNA abundance and binding site densities in various neocortical and hippocampal regions of schizophrenics and control subjects. Age, agonal state (brain pH), and post mortem interval were included where necessary as covariates in our analyses. In schizophrenics, 5-HT1A binding site densities, determined autoradiographically by [3H]8-hydroxy-2,3-(dipropylamino)-tetralin ([3H]8-OH-DPAT), were significantly increased (+23%) in the dorsolateral prefrontal cortex, with a similar trend in anterior cingulate gyrus. These increases were not accompanied by any change in 5-HT1A receptor mRNA. No differences between the groups in [3H]8-OH-DPAT binding or 5-HT1A receptor mRNA were seen in superior temporal gyrus, striate cortex, or hippocampus. 5-HT2A binding sites, determined by [3H]ketanserin, were decreased in the dorsolateral prefrontal cortex (-27%) and parahippocampal gyrus (-38%) of schizophrenics, with a similar trend in cingulate gyrus, but not in superior temporal gyrus or striate cortex. 5-HT2A receptor mRNA abundance was reduced in schizophrenics in the dorsolateral prefrontal (-49%), superior temporal (-48%), anterior cingulate (-63%) and striate (-63%) cortices, but not in parahippocampal gyrus. Parallel analyses of rat brain tissue showed no changes in 5-HT1A or 5-HT2A receptor mRNAs or binding site densities after chronic administration of haloperidol. These data show that schizophrenia is associated with alterations in the expression of central 5-HT1A and 5-HT2A receptors. They confirm reports of increased 5-HT1A and decreased 5-HT2A binding site densities in prefrontal cortex, and reveal more extensive decreases in 5-HT2A receptor gene expression at the mRNA level. The resulting imbalance in the 5-HT1A to 5-HT2A receptor ratio, when considered in terms of the chemoarchitectural distribution of these receptors, may contribute to an impairment of corticocortical association pathways. The apparent dissociation of the normal relationships between the abundance of each 5-HT receptor and its mRNA in schizophrenia introduces a separate complexity to the data, which may give clues to the underlying molecular mechanisms.