Gonadectomy and sex differences in the behavioral responses to amphetamine and apomorphine of rats

Following treatment with 5 mg/kg d-amphetamine sulfate or 2 mg/kg apomorphine hydrochloride female rats displayed more intense and longer lasting stereotyped behavior than males. Gonadectomy did not affect the display of stereotyped behavior induced by either drug in either sex. A lower dose of amphetamine (1 mg/kg) caused greater stimulation of locomotor activity in females than in males. Castration of males had no effect, but ovariectomy blocked the stimulating effect of amphetamine on activity. By contrast, low doses of apomorphine depressed activity in a dose-dependent manner that was somewhat greater in ovariectomized females than in the other groups. These data add to the growing body of literature demonstrating that gonadal hormones modulate the activity of brain dopamine systems.