Effects of drugs on behaviour of aggressive mice.

1 The occurrence of 11 aggressive and non-aggressive activities was observed in aggressive male mice treated with drugs in paired interactions with non-aggressive males given water. Effects of chlordiazepoxide, diazepam, barbitone, chlorpromazine, imipramine, (+)-amphetamine, lysergic acid diethylamide (LSD) all given orally and of intraperitoneal scopolamine were investigated.2 Scopolamine (0.25 and 0.75 mg/kg), (+)-amphetamine (0.25 and 1 mg/kg), chlorpromazine (2.5 mg/kg), diazepam (10 mg/kg) and chlordiazepoxide (50 mg/kg) reduced aggressive activities (attacks, aggressive unrest) without inhibiting walking across the cage or rearing in the aggressive mice. Thus, the inhibition of aggression induced by these drugs does not seem to be due to neuromuscular impairment and seems to this extent specific. On the other hand, imipramine lessened aggressive activities only at a dose (80 mg/kg) which also decreased walking across the cage and rearing. Barbitone or LSD did not change aggression at either dose tested (20 and 60 or 0.01 and 1 mg/kg, respectively). Aggressive activities were increased significantly only by chlordiazepoxide at a dose of 5 mg/kg.3 (+)-Amphetamine (0.25 mg/kg) and scopolamine (0.75 mg/kg) increased escapes and alert postures, respectively, in the aggressive mice.4 Diazepam and chlordiazepoxide decreased tail rattling at 1 and 5 mg/kg, respectively, doses 10 times lower than those inhibiting attacks. The other drugs tested inhibited tail rattling only at doses reducing attacks. Tail rattling appears to be a convenient measure for testing effects of drugs on behavioural conflict.5 Diazepam (5 and 10 mg/kg), chlordiazepoxide (20 and 50 mg/kg), barbitone (60 mg/kg) and scopolamine (0.25 and 0.75 mg/kg) increased sociable activities (sniffing, following partners and climbing over them) whereas (+)-amphetamine, chlorpromazine, imipramine and LSD did not. Effects of the drugs on sociable activities in aggressive mice seem to correlate with their action on punished responding and other types of suppressed behaviour.