Effect of metergoline,fenfluramine, and 8-OHDPAT on catalepsy induced by haloperidol or morphine

Summary The influences of the indirect serotonin agonist fenfluramine (5; 10 mg/kg s.c.), the serotonin antagonist metergoline (5; 10 mg/kg s.c.) and the 5-HT_1A agonist 8-OHDPAT (0.1; 0.2; 0.46 mg/kg s. c.) on haloperidol-induced catalepsy in rats or mice and on morphine-induced catalepsy in rats were studied. Morphine-induced catalepsy was enhanced by fenfluramine and attenuated by metergoline, whereas neither fenfluramine nor metergoline had any effect on haloperidol-induced catalepsy. 8-OHDPAT strongly antagonised catalepsy induced by morphine or haloperidol. We conclude that serotonergic transmission plays a major role in effectuating morphine catalepsy but not in effectuating haloperidol catalepsy. The antagonistic effect of 8-OHDPAT suggests a secondary, modulating role for 5-HT_1A receptor mediated events in both types of catalepsy.Send offprint requests to C. L. E. Broekkamp at the above address