Social status as determinant of alcohol effects on aggressive behavior in squirrel monkeys (Saimiri sciureus)

We investigated the behavioral effects of alcohol, especially those on aggression, on members of established groups of squirrel monkeys. A continuous measurement of monkey behavior in groups revealed consistent differences between dominant and subordinate animals. Dominant monkeys aggressed more frequently than subordinate monkeys, and spent less time in stationary postures. Alcohol produced dose-related biphasic changes in the number of threats, grasps, and displacements exhibited by dominant but not subordinate monkeys. Low doses of alcohol (0.1, 0.3, 0.6 g/kg) increased the frequency of aggressive behavior, and high doses (1.0 g/kg) decreased these behaviors. The largest change in behavior was evident in the first 20-40 min after injection, with a return to baseline 60-120 min later. The aggression-enhancing effect of alcohol in dominant monkeys required a stable baseline, which was obtained by daily administration of distilled water. Low levels of aggressive and associative behavior in subordinate monkeys were relatively unaffected at any dose of alcohol. They were associated with and aggressed against more often by untreated members of the group. The status-dependent effects of alcohol may be related to the neuroendocrine and neurotransmitter profiles characteristic of dominant and subordinate monkeys.