Stereotyped behavior elicited by amphetamine in the rat: influences of the testes.

Castrating male rats in adulthood increased the duration of stereotyped behavior in responses of 5 mg/kg injections of d-amphetamine sulfate; exogenous treatment with testosterone propionate (TP) reversed this effect. Ovariectomy in adulthood had no effect on stereotypy, but TP injections reduced stereotyped responding by ovariectomized females. Thus testosterone exerts comparable effects on stereotypy elicited by amphetamine in both sexes. Males castrated at 1, 6 or 10 days of age but not males castrated in adulthood displayed levels of stereotyped behavior comparable to those of ovariectomized females when all animals were given TP in adulthood. Control experiments indicated that age of castration rather than time since castration was the critical factor, implying that secretions of the testes early in life exert effects on systems that regulate the responses of adults to amphetamine.