Fenfluramine challenge, self-injurious behavior, and aggression in rhesus monkeys

Self-injurious behavior (SIB) and aggression have been linked to reduced serotonergic (5-HT) functioning in both humans and nonhuman primates. The present study examined serum prolactin and cortisol responses to the 5-HT releasing agent D,L-fenfluramine (FEN) in 24 individually housed rhesus monkeys (Macaca mulatta), 15 of which carried a veterinary record of self-wounding (SW). Subjects received two doses of FEN, 4 and 2 mg/kg, separated by an interval of at least 2 months. For control purposes, monkeys were given an intramuscular saline injection 1 week prior to each FEN challenge. The relationship between the hormonal responses to FEN, wounding history, the rates of self-directed biting and aggression were determined for each animal based on 100 five-minute observations conducted over a period of 12 months surrounding the challenge procedures. Prolactin and cortisol responses to FEN were unrelated either to wounding history or to rates of self-directed biting. However, there were significant inverse correlations between levels of aggression and the prolactin response to both doses of FEN. The present findings provide no evidence for reduced 5-HT system function in rhesus monkeys with SIB under the present challenge conditions. However, the results are consistent with a previously reported inverse relationship between serotonergic activity and aggression. Moreover, a dose-dependent response to FEN was observed only for prolactin, suggesting that this variable is more appropriate than cortisol as an endpoint for FEN challenge in monkeys.