Comparison of the effects of alcohol, chlordiazepoxide, and delta9-tetrahydrocannabinol on intraspecies aggression in rats.

The species-specific repertoire of attack, threat, defense, and submission was produced in pairs of male laboratory rats and measured after intraperitoneal injection of a drug or its vehicle to one of the rats. Attack behavior by dominant rats toward nondrugged opponents was increased by a low dose of alcohol (0.5 g/kg) or of chlordiazepoxide (5 mg/kg), but suppressed by delta9-tetrahydrocannabinol (THC). In experienced subordinate rats, the highest alcohol dose (1.5 g/kg) impaired the defensive upright posture whereas THC (2, 4 MG/KG) prolonged immobile crouch and submissivesupine reactions and resulted in more wounds. Naive rats administered alcohol assumed the submissivesupine posture more readily and for a longer duration, but sustained more biting attacks. Chlordiazepoxide and THC, when administered to naive rats, prolonged the immobile crouch reaction, and THC also impaired the defensive upright posture. We conclude that alcohol and chlordiazepoxide both enhance attack behavior in dominant rats, whereas THC has specific anti-aggressive effects and profoundly alters the submissive-defensive reactions.