Risperidone, an atypical antipsychotic, affects the mRNA expressions of monoamine oxidase type B and vesicular monoamine transporter-2 in rat brain

To determine if the antagonism of serotonin 5HT(2A) receptors and dopamine D-2 receptors by risperidone alters the mRNAs encoding the transporters and enzymes that are involved in re-uptake of serotonin and dopamine and in the degradation and refilling of secretory vesicles, we employed semi-quantitative HT-PCR on rats given risperidone. The rats were given twice daily a subcutaneous injection of either 0.3% tartaric acid (vehicle) or risperidone (0.5 mg/kg) for 21 days and sacrificed one hour after the last injection. Risperidone enhanced the level of monoamine oxidase type B (MAO-B) mRNA in the brainstem (P<0.05) and that of vesicular monoamine transporter-2 (VMAT2) mRNA in the hypothalamus (P<0.05) when these levels were compared with the control ones, whereas there were no significant group differences in other mRNAs examined. The antagonism of 5HT(2A) and D-2 receptors may thus affect the monoamine levels by regulating mRNAs encoding MAO-B and VMAT2.