Intermale Aggression in Mice: Modification by Postneonatal Castration 1

Abstract

Summary

Male mice were castrated between 21 and 55 days of age and received testosterone propionate replacement for 14 days through either 35-40 days or 85 days of age. At the above ages, animals were paired and aggressiveness was evaluated using incidence of fighting. Fighting was prevented in 35-40-day-old males by castration and androgen therapy at a level known to sustain aggressiveness among animals castrated post-pubertally or late during puberty. Incidence of aggression also was considerably reduced among males castrated when 21 or 35 days old and receiving androgen replacement as adults. On the other hand, castration at 45 or 55 days of age failed to reduce androgen-induced aggressiveness among adults. It is postulated that normally rising plasma levels of testicular hormones in the prepubertal male house mouse influence development of neural systems associated with intermale aggression.