Anti-aggressive effect of high doses of testosterone propionate is modulated by the type of opponent

We set out to determine whether behavioural effects of chronic exposure to high doses of testosterone propionate (TP) could be modulated by the type of opponent used in social encounters in OF-1 male mice. After three weeks of isolation, animals were pre-screened for aggression in a social encounter. From the fifth to the 14th week, subjects were injected once a week with TP (60 or 120 mg/kg) or vehicle (sesame oil). 24 h after the last injection another social encounter was initiated, where 40 mice confronted anosmic opponents whereas another 44 confronted non-anosmic opponents. When anosmic opponents were used, animals showed a significantly lower frequency of attack and threat; a significantly lower frequency and total duration as well as shorter latency of avoidance/flee; and significantly shorter latency of social exploration and digging than when confronting non-anosmic opponents. Moreover, TP-treated groups showed significantly lower frequency and duration of attack than controls. Med Sci Res 27:765-767 (C) 1999 Lippincott Williams & Wilkins.