Circling behavior in mice and rats: possible relationship to isolation-induced aggression.

The relationship between circling behavior (rotation), isolation, and aggression was investigated in normal male mice and rats. Initially the animals were tested for spontaneous nocturnal rotation, then conspecific aggression and muricidal behavior was observed for mice and rats respectively. Subsequently, animals were paired on the basis of net nocturnal rotations and either group-housed or individually housed. Four weeks later all animals were retested for the same behaviors. Spontaneous nocturnal rotation increased significantly for the isolated mice but not for the group-housed animals. Moreover, 9 of the 10 isolates became aggressive and their net rotations were significantly and positively correlated with the number of biting attacks. None of the group-housed mice became aggressive. Rats, on other hand, showed a decrease in rotation and a relationship between rotation and muricidal behavior was not evident. The possible relationship between circling behavior, aggression, and territoriality is discussed.