Effects of a short period of isolation in adulthood on the aggressive behavior of dominant and subordinate male mice

Male ddY mice were used to investigate the effect of a short period of isolation in adulthood on aggressive behavior. The relationship between the dominance status previous to isolation and the effect of isolation was investigated. The mice were kept in isolation for 3 weeks from 9 weeks of age, during which intruder tests were conducted once a week. They then went through an encounter test, in which the mice encountered dominant or subordinate mice in a neutral space. The number of the formerly-dominant isolated mice that attacked the intruder mice decreased at first and then increased. The latency to attack also lengthened at first and then shortened. Seven former-dominants continued to show aggression throughout the experiment. The number of the formerly-subordinate isolated mice that attacked the intruder mice increased linearly. But 3 former-subordinates did not show aggression through the entire experiment. After 3 weeks isolation, the number of mice that showed aggression and the amount of aggression did not differ between the former-dominants and subordinates. Isolation housing was concluded to differentially affect the dominant and subordinate mice during the 3 weeks of isolation. It was also concluded to differentially affect the mice of absolute dominance and relative dominance differentially. The aggressive behavior of the isolated mice appears to occur independently of site.