Behavioral, hormonal and neurochemical characteristics of aggressive α-mice

The present study examined the behavioral, neurochemical and endocrinological characteristics of aggressive, male α-mice. These mice inflict severe bite marks on other male mice in their cage, but are not attacked themselves. The characteristics of the α-mice were compared with those of submissive mice, and of control mice taken from cages in which no severe fighting was observed. The behavioral tests used were Porsolt's swim test of behavioral 'despair', a plusmaze test of anxiety, a holeboard test of exploration and locomotor activity, and a test of seizure threshold to bicuculline. The α-mice were found to be immobile in the swim test for a shorter time than the submissive and control mice, and the submissive mice for a longer time than the controls. In the holeboard, the α-mice spent less time making exploratory head-dips than the other mice. Submissive mice had elevated 5-HIAA levels in the hypothalamus, hippocampus and brainstem, and the alpha mice had reduced concentrations of dopamine in the brainstem. There were no significant differences in plasma corticosterone or testosterone concentrations between the groups. These findings indicate that in α-mice, a number of behavioral and neurochemical characteristics appear together with the unusually high aggressiveness towards cage-mates.