Mechanisms underlying the absence of the pubertal shift in the playful defense of female rats.

Due to the action of testicular hormones in the perinatal period, juvenile male rats engage in more play fighting than juvenile females. Also, following puberty, males, but not females, switch to using adultlike defensive tactics more frequently during play. This change in play is also due to the action of testicular hormones perinatally. In this study, two experiments were conducted to determine if the pubertal transition in defense could be induced in females. For Experiment 1, male and female cagemates were tested before and after puberty with familiar and unfamiliar partners. Even when playfully interacting with subadult males, females did not increase the use of the adultlike defensive tactics. For Experiment 2, neonatal females were either injected with testosterone propionate (TP) or ovariectomized (OVX), and again tested before and after puberty. While the TP-treated females had higher frequencies of play fighting, they did not change their pattern of defense following puberty. The OVX females exhibited the lower frequency of play fighting typical of females, but changed their pattern of defense with increased age. Thus, it appears that the pattern of pubertal change in playful defense typical of males is inhibited by ovarian hormones. The mechanisms by which ovarian hormones could exert this effect on developing females are discussed.