Contrasting effects of d-amphetamine on affiliation and aggression in monkeys

Amphetamine has been observed to alter conditioned or learned behavior in individually housed animals, as well as naturally-occurring behavior characteristic of animals living in groups. This study is concerned with the effects of d-amphetamine on affiliative and aggressive behavior in adult male stumptail macaques (Macaca arctoides) living in a large, heterogeneous social group. Using standardized observational techniques, the affiliative and aggressive behaviors initiated by five adult male monkeys were characterized and quantitated in the absence of and following drug administration. Acute administration of a range of doses of d-amphetamine (0.003-0.56 mg/kg) resulted in a monotonically depressive effect on the rate of affiliative behavior initiated by the experimental animals. In contrast, d-amphetamine increased the rate of aggressive behavior initiated by the highest- and lowest-ranking monkeys, and had little or no effect in the mid-ranking monkeys. These results show that d-amphetamine can have qualitatively different effects on affiliative and aggressive behavior in the same subjects. The results also provide evidence that the effects of d-amphetamine can be determined by the hierarchical or dominance position of the subject in the group.