Androgen-dependency of aggressive target-biting and paired fighting in male mice

The effect of gonadal hormone manipulations by means of castration and/or exogenous injections on aggressive biting of an inanimate bite-target and wheel running by mice was studied. Castration lowered the bite-attack levels of mice but daily injections of testosterone restored these bite attack levels to that of intact mice. Cessation of the testosterone replacement was again followed by lower bite attack levels. Running activity was monitored to assure specificity of independent variable manipulations and standard paired fighting tests were conducted for comparison with traditional methods. There was a high correlation between the number of paired fight responses and the total number of inanimate target attacks. Running activity did not vary across treatments. Results indicate that androgen is critical for the maintenance of biting attack in males, that androgen affects aggression without altering running, that there is a maximal effect beyond which additional androgen produced little change, and that the single subject paradigm utilized in this study is an effective model for the study of pharmacological and physiological effects on aggressive behavior.