The anxiogenic drug FG7142 increases self-injurious behavior in male rhesus monkeys (Macaca mulatta).

AIMS

Self-injurious behavior (SIB), which is deliberate infliction of self-injury without suicidal intent, is a significant human health problem. SIB is not unique to humans but is also manifested in a small percentage of captive macaques, typically as self-directed biting. Although the onset and maintenance of SIB have been linked to increased anxiety in both humans and nonhuman primates, no previous studies have directly tested the anxiety-SIB hypothesis. Here, we determined whether rhesus monkeys increase their self-directed biting following a challenge with the anxiogenic compound N-methyl-beta-carboline-3-carboxamide (FG7142).

MAIN METHODS

Ten rhesus monkeys (Macaca mulatta) with a veterinary record of self-wounding (SIB) as well as six age- and weight-matched non-wounding control monkeys were given intramuscular injections of 0.1, 0.3, or 1.0mg/kg FG7142. Behavior was observed following drug administration with special attention to displacement behaviors (scratching, self-grooming, and yawning), locomotor stereotypy, and self-directed biting. Plasma cortisol and ACTH were also measured as physiological indices of stress.

KEY FINDINGS

Self-directed biting rates dose-dependently increased in a subset of SIB monkeys, but did not change in control animals. Furthermore, administration of FG7142 led to an increase in scratching, yawning, and locomotor stereotypy in all monkeys, but did not affect the frequency self-grooming. Additionally, there was a dose-dependent increase in plasma cortisol concentrations, but not ACTH, in all animals.

SIGNIFICANCE

The present findings indicate that self-biting is anxiety-related in some but not all SIB monkeys, suggesting that this behavioral pathology is heterogeneous as has previously been suggested for SIB in humans.