Testosterone removal in rats results in a decrease in social aggression and a loss of social dominance.
Alpha male rats from mixed sex colony groups were tested for aggressiveness toward nonaggressive male intruders. Afterward, they were castrated and implanted with testosterone filled Silastic tubes, castrated and implanted with empty tubes, or sham castrated and implanted with empty tubes. There were significant declines in the aggressiveness (lateral attacks, bites, and piloerection but not on-top) of castrated rats without testosterone replacement but not in castrated rats with testosterone replacement. At a second operation, castrated animals had their testosterone capsules removed or had their empty capsules replaced with testosterone filled capsules. When tested for aggression toward nonaggressive intruders, those alpha males which had testosterone removed declined in aggressiveness while those which had it implanted returned to a level of aggressiveness close to that emitted by sham castrated control animals. Subordinate males became dominant when alpha males were castrated and not given testosterone replacement. In a final series of observations, sham castrated males were found to be more aggressive than castrated males when pitted against one another. It is argued that testosterone plays a primary role in intermale social aggression and that the decline in aggressiveness following castration is typically accompanied by a loss of social dominance.