Implants of testosterone into the septal forebrain activate aggressive behavior in male mice

Thstosterone has a modulatory role in the control of aggressive behavior in male mice. To determine where within the forebrain testosterone might be exerting this modulation, we implanted testosterone into discrete brain regions in castrated male mice and then assessed their level of aggression. Male mice were castrated, and 3 weeks later a 23‐gauge guide cannula was implanted into the medial preoptic area (MPOA), septum, or caudate nucleus. Twice per week, they received approximately 3 μg of testosterone or cholesterol through 30‐gauge cannulae. The day after hormone or control treatment, the mice were tested for aggressive behavior by confronting them with an intruder. Septal implants of testosterone were effective in restoring male aggressive behavior. The frequency of attacks in the groups receiving testosterone in the MPOA or caudate did not differ from that of the cholesterol‐treated controls. Testosterone implanted into any of these three sites did not alter nonaggressive behaviors. The septum appears to be an important site for testosterone mediation of aggressive behavior in mice. This result is consistent with earlier work with male mice; however, unlike the present experiment, earlier research in rats has alsofound the MPOA to be a site sensitive to the aggression promoting actions of testosterone. This may represent a species difference in hormonal control or reflect differences in methodology.