NEW TEST FOR AGGRESSION IN RATS WITHOUT AVERSIVE-STIMULATION - DIFFERENTIAL EFFECTS OF D-AMPHETAMINE AND COCAINE

A procedure was developed which reliably engenders agonistic behavior between alpha males of small colonies of laboratory rats and intruder rats. Drugs were administered either to the alpha resident male rat, who showed the pattern of attack and threat behavior, or to the intruder rat, who engaged in defensive, submissive and flight reactions. The 5 min test also permitted assessment of drug effects on nonagonistic social and solitary behavior. d-Amphetamine administration at a very low dose (0.063 mg/kg) to resident alpha rats increased the frequency of their attacks, sideways threats and pursuits, while low doses of cocaine (0.5, 2.0 mg/kg) failed to alter any of these behaviors significantly. Attack and threat behavior was effectively decreased by 0.25-1.0 mg/kg d-amphetamine and by 8 and 32 mg/kg cocaine. The antiaggressive effects of amphetamine, but not cocaine, were accompanied by a marked increase in nonagonistic rearing and walking. Amphetamine administration to intruder rats increased nonagonistic locomotor activity and caused the intruders to be attacked more frequently, to escape more often and to emit fewer ultrasonic vocalizations. Cocaine did not alter significantly the intruders'' behavior. The resident-intruder situation appears to be a reliable, easy-to-use procedure detecting differential behavioral behavioral effects of psychomotor stimulants, such as d-amphetamine and cocaine, while avoiding the confounding influence of aversive stimulation, conditioning and screening of suitable subjects typically associated with agression tests in the laboratory.