Testosterone dependent effects of methylphenidate on social investigatory behavior of the rat

Previous work suggested a sex difference in social investigatory behavior of a novel conspecific during acute exposure to methylphenidate. In contrast to caffeine, which has been observed to increase social investigatory behavior only in males, methylphenidate decreased social investigatory behavior only in females. Testosterone-treated females were comparable to males and were unaffected by methylphenidate. Castrated males were comparable to females in their sensitivity to methylphenidate. Like caffeine, methylphenidate increased locomotor activity in both males and females, suggesting that drug effects on social investigation cannot be attributed to a nonspecific stimulant effect. The combined results reveal a sex-related interaction of circulating testosterone with acute methylphendiate exposure. Interpretations are discussed including the behavioral contrast following exposure to methylphenidate or to caffeine.