Inter-group aggression in mice: a new method for testing the effects of centrally active drugs

A new method is described with which the effects of drugs on aggressive behaviour can be compared with their effects on general activity. Two groups of 3 male mice are housed in either half of a macrolon living cage which is divided down the middle by a non-transparent barrier. After 21 days the cage is placed on an activity meter and the dividing wall is removed. The ensuing fighting is scored by an observer and at the same time activity is measured using the activity meter. It was shown that aggression occurred mainly between groups with the dominant members doing most of the fighting. It appeared further that the two parameters measured--aggression and motor activity--respond differentially to the effects of standard psychotropic drugs. By this means it was possible to distinguish between the effects of chlorpromazine, pentobarbitone, chlordiazepoxide and d-amphetamine. In addition it was possible to confirm that an experimental compound, YG 19-256, which in other tests has been shown to inhibit aggressive behaviour without causing general sedation, also has selective anti-aggressive effects in this test. From these results it seems that the intergroup aggression test could well be useful in identifying different classes of psychotropic agents.