Physiological correlates of self-injurious behavior in captive, socially-reared rhesus monkeys

This study examined the relationship between self-injurious behavior (SIB) in rhesus monkeys and several biological variables, including monoamine met abolites in cerebrospinal fluid (CSF) and circulating levels of ACTH, corti sol, and testosterone. Cisternal CSF and blood plasma samples were obtained from 23 individually housed male rhesus macaques, 14 of which had a veteri nary record of self-inflicted wounding. CSF samples were analyzed for 5-hyd roxyindole-3-acetic acid (5-HIAA), homovanillic acid (HVA) and 3-methoxy-4- hydroxyphenylglycol (MHPG) using isocratic high-performance liquid chromato graphy with electrochemical detection (HPLC-EC). Plasma samples were analyz ed for ACTH, cortisol, and testosterone using commercially available radioi mmunoassays (RIAs), Rates of self-directed biting were determined by system atic observation of all monkeys. Monkeys with SIE did not differ from contr ols in their basal monoamine or gonadal activity. However, the SIE group sh owed consistently lower mean plasma cortisol levels than the control group. Plasma cortisol was negatively correlated with rates of self-directed biti ng. These results suggest a persistent dysregulation of the hypothalmic-pit uitary-adrenal (HPA) axis in monkeys with SIE. It is not yet clear whether this phenomenon of low cortisol represents chronically reduced adrenocortic al secretion under basal conditions or a difference in response to the mild stress of capture and chemical restraint. The implications of these findin gs will be discussed with respect to SIE in humans as well as post-traumati c stress disorder (PTSD), a condition characterized by pituitary-adrenocort ical hypoactivity. (C) 2000 Elsevier Science Ltd. All rights reserved.