Analysis of amphetamine effects on agonistic and affiliative behavior in squirrel monkeys (Saimiri sciureus)

Two series of experiments were performed to differentiate the effects of d-amphetamine on social interactions from those on solitary motor behavior in adult and juvenile squirrel monkeys. In the first experiment, d-amphetamine (3x0.5 mg/kg, PO) induced pronounced stereotyped movements of the head, limbs and torso. When confronted in the colony room with an intruder monkey, the amphetamine-treated resident monkey showed reduced threat and attack behavior. In a separate test for affiliation, amphetamine nearly abolished the affiliative response toward a familiar group member. In a second series of experiments, d-amphetamine (0.3, 1.0 mg/kg, IM) decreased the affiliative behavior of juvenile monkeys towards their mothers; yet, in the presence of an unfamiliar adult male, the detrimental effect of amphetamine on affiliative behavior was prevented. Morphine (0.5, 2.0 mg/kg) increased the affiliative response toward the mother, and chlordiazepoxide (5, 10 mg/kg) was without effect in this situation. These observations suggest that amphetamine impairs a range of social behavior in adult and juvenile monkeys. The general disruption of agonistic and affiliative behaviors due to amphetamine appears to be based on mechanisms which differ from those mediating stereotyped movements. Stimulant-induced changes in social interactions in primates may be linked to disturbed affect.