Genetic differences in female house mice in aggressive response to sex steroid hormone treatment.

Male mice, genetically selected for aggression, characterized by short attack latency (SAL) or long attack latency (LAL), differ on several testosterone (T)-related parameters during ontogeny and adult age. The variation in aggressive behavior at adult age may be due to differences in degree of androgenization prenatally. When exposed to T at prenatal, neonatal, and/or adult age, nonlactating females also display intraspecific fighting behavior. In the present study, we investigated in females of the SAL and LAL selection lines, whether the differentiation of aggression involves processes similar to ones seen in males. Therefore, we injected females with testosterone propionate (TP) or vehicle on the day of birth, treated them after ovariectomy at adult age with T, estradiol (E), or vehicle, and tested their aggressive response. We found that neonatally vehicle-treated SAL females show a higher aggressive response to chronic T treatment at adult age than LAL females receiving the same treatment. Females of both selection lines treated with vehicle or E as adults were not aggressive. Neonatal TP treatment did not influence the adult T sensitivity and difference between selection lines in response to T at adult age. However, neonatally TP-treated SAL females showed aggressive behavior when treated with E at adult age, whereas LAL females failed to do so. These results suggest a genetic difference in susceptibility to T and E, which plays a major role prenatally, in organizing the development of sex steroid-dependent neural systems.