Regional [3H]testosterone uptake in the brain of isolated non-aggressive mice.

Male mice which are housed individually develop a characteristic aggressive, 'fighting' behavior. A small percentage of mice so isolated fail to become aggressive and in fact, behaviorally are strikingly different in that they develop a 'timid' behavior. Isolation-induced aggression is an androgen-dependent behavior and androgen-sensitive neurons have been identified in mouse brain, mainly in the limbic system. When intact isolated aggressive mice and isolated and aggregated non-aggressive mice were injected with radioactive testosterone and sacrificed after 30 min no remarkable differences in uptake of radioactive testosterone occurred in various brain areas. However, in castrated animals the uptake of testosterone was greatly enhanced in the isolated non-fighters whereas testosterone uptake in the isolated fighters and aggregated non-fighters was in the range of the intact animals. This study represents, for the first time, a documented hormonal difference between isolated aggressive and non-aggressive animals.