Feminine dimension in the play fighting of rats (Rattus norvegicus) and its defeminization neonatally by androgens.

In rats (Rattus norvegicus), juvenile males engage in more play fighting (a male-typical behavior) than do juvenile females, and this difference is based on perinatal influences of androgens. We show that there are qualitative and quantitative differences between the sexes in the type of defensive responses and their manner of execution. In defensive responses rats try to avoid having their napes contacted by the partner's snout. The sex differences arise from females' greater response distance; that is, females responded to an approach when the partner's snout was further from the nape. This permits females to use different defensive responses and to use them more successfully. This greater response distance is defeminized by the neonatal administration of testosterone propionate. Our findings suggest that play fighting in rats has both male- and female-typical features and that these are, at least in part, influenced perinatally by androgens.