[Effects of risperidone on catalepsy and cerebral dopamine, serotonin and GABA metabolism in the rat: comparison with haloperidol].

Effects of risperidone (RIS, 1 mg/kg) and haloperidol (HPD, 1 mg/kg) on catalepsy, and monoamine and GABA metabolism were examined in the rats. Catalepsy was evaluated by means of a horizontal bar method. The rats were sacrificed 3 h after orally administered HPD or RIS. Levels of monoamines and their metabolites determined by HPLC-ECD, and GABA levels were determined by a radioreceptor assay. The score of catalepsy was significantly low 120 min after administration of RIS as compared to HPD. In comparison to control, HPD treatment significantly increased DOPAC in the frontal cortex, thalamus + hypothalamus, and striatum, and HVA in the striatum. In RIS-treated rats, DOPAC and HVA were significantly increased in the striatum. Moreover, RIS increased 5-HIAA in the frontal cortex, hippocampus, thalamus + hypothalamus, mid brain, pons and striatum. The concentration of GABA was unchanged in all areas of the brain after treatment with HPD, but was significantly decreased in the pons in RIS-treated rats. The present results suggested that the effects of RIS on serotonin and GABA metabolism may be related to the cause of the low potency of RIS to induce catalepsy.