Antagonism by pimozide of olanzapine-induced hypothermia

The atypical antipsychotic olanzapine (2.5-20 mg/kg) produced hypothermia i n Fats. The decrease in rectal temperature caused by olanzapine (2.5-20 mg/ kg) was blocked by the selective dopamine D-2 receptor antagonist pimozide (0.5 and 1 mg/kg) but not by the dopamine D-1 receptor antagonist SCH 23390 (0.5 and 1 mg/kg). The dopamine D-1/D-2 receptor agonist apomorphine (3 mg /kg) and the selective dopamine D-2 receptor agonist talipexole (0.5 mg/kg) produced hypothermia in rats. Olanzapine (10 and 20 mg/kg) significantly b locked hypothermia produced by both apomorphine and talipexole while the lo wer doses (2.5 and 5 mg/kg) of olanzapine failed to block it. The present r esults demonstrate that olanzapine behaves as a partial agonist at brain DA D1 receptor populations involved in thermoregulation in the rat. (C) 1999 Editions scientifiques et medicales Elsevier SAS.