Testosterone and persistance of social investigation in laboratory rats.

In a series of experiments, mature male and female rats were individually exposed in their home cages to sexually immature conspecifics. A prominent sex difference was observed in duration of social investigation prior to a criterion of neglect. When pups were 5 days of age, no sex difference was observed, but when pups were 8 days of age and older, mature males consistently investigated them for significantly longer intervals than did mature females. Furthermore, intact males investigated prepuberal conspecifics for significantly longer intervals than did castrated males, castrated females, or intact females; none of the latter three groups differed significantly from each other. Following testosterone treatment, castrated males investigated unfamiliar, prepuberal conspecifics for a significantly longer duration than did untreated castrated control animals. The combined results support the conclusion that gonadal testosterone effects a greater perseveration of social investigation in males.