Differential regulation of D2 and D4 dopamine receptor mRNAs in the primate cerebral cortex vs. neostriatum: effects of chronic treatment with typical and atypical antipsychotic drugs.

The RNase Protection Assay was used to examine the regulation of D2 and D4 dopamine receptor mRNAs in the cerebral cortex and neostriatum of nonhuman primates after chronic treatment with a wide spectrum of antipsychotic medications (chlorpromazine, clozapine, haloperidol, molindone, olanzapine, pimozide, remoxipride and risperidone). Tiapride, a D2 antagonist that lacks antipsychotic activity, was also included. All drugs were administered orally for 6 months at doses recommended for humans. All antipsychotic drug treatments examined in this study caused a statistically significant up-regulation of both the long and short isoforms of the D2 receptor mRNAs in the prefrontal and temporal cortex. Tiapride, in contrast, significantly up-regulated only the level of D2-long mRNA in these areas. The same drug treatments produced less uniform effects in the neostriatum than in the cortex: clozapine and olanzapine failed to significantly elevate either D2-long or D2-short receptor messages in this structure unlike all other drugs, including tiapride. In both the cerebral cortex and striatum, D4 receptor mRNA was upregulated by certain typical (chlorpromazine and haloperidol) and certain atypical (clozapine, olanzapine and risperidone) antipsychotic agents as well as by tiapride. Other drugs of the typical (molindone and pimozide) and atypical (remoxipride) classes had no effect on D4 mRNA levels in either cortical or striatal tissue. The finding that up-regulation of D2 dopamine receptor mRNAs was a consistently observed effect of a wide range of antipsychotic agents in the cerebral cortex but not in the neostriatum, coupled with the fact that the D2-short isoforms in the cortex were not regulated by a nonantipsychotic D2 antagonist, tiapride, draws attention to the importance of the D2 dopamine receptor in the cerebral cortex as a potentially critical, common site of action of antipsychotic medications.