Persistence of attention to a novel conspecific: some developmental variables in laboratory rats

Persistence of social attention by male and female laboratory rats was examined following exposure to novel conspecifics. In experiment I we compared performance of castrate female controls. Testosterone significantly prolonged mean social investigation time. Castrate females treated with a 10-day regimen of testosterone propionate to that of intact males and castrate females treated with a relatively high dosage of testosterone failed to differ from intact males. In Experiment II we compared neonatally androgenized female castrates with castrate male and castrate female controls. Postnatal exposure to testosterone increased sensitivity of females to exogenous testosterone in maturity as measured by persistence of social investigation. In Experiment III we compared investigation time of intact and castrate males and females at 10-day intervals from 40 to 80 days of age. Intact males investigated novel conspecifics significantly longer than other groups, with longest investigation times at 60 and 70 days of age. In Experiment IV we compared investigation times of 30-day, 60-day, and 200-day-old males. Sixty-day-old males investigated significantly longer than 30-day-old or 200-day-old groups, which failed to differ from each other. The combined results demonstrate a gender and age-related effect of testosterone on persistence of social investigation.