EFFECTS OF TESTOSTERONE EXPOSURE AND FIGHTING EXPERIENCE ON THE AGGRESSIVE-BEHAVIOR OF FEMALE AND MALE-MICE SELECTIVELY BRED FOR INTERMALE AGGRESSION

Exposure of female mice to testosterone resulted in aggressive behavio r as a function of breeding line in two lines of mice selectively bred for high (Turku Aggressive, TA) and low (Turku Nonaggressive, TNA) le vels of aggressiveness. Female TA mice that received a single injectio n of testosterone propionate (TP) (1 mg in 0.05 ml peanut oil) on the second day of life, and starting at 120 days of age received dairy inj ections for seven consecutive days, displayed aggressive behavior on a level comparable to that of socially isolated males of the same line, whereas control TA females (injected with 0.05 ml peanut oil) and TP- exposed TNA females were totally nonaggressive. The level of aggressiv eness was assessed by means of dyadic tests against intact male oppone nts. Early and adult exposure to TP did not lead to increased aggressi veness in male TNA mice. Fighting experience in combination with prolo nged TP treatment changed the aggressiveness of the TP-exposed TA fema les, leading to decreased aggressiveness in defeated animals. The gene tically correlated low level of aggressiveness of TNA male and female mice was unaffected by any combination of TP exposure, learning and so cial isolation. It is concluded that differences in testosterone react ivity of target organs, other than those which are Y chromosome determ ined, i.e., the testes, are responsible for the aggressiveness in the strains studied. (C) 1994 Academic Press, Inc.