Self‐injurious behavior in rhesus monkeys: New insights into its etiology, physiology, and treatment

Abstract

Self-injurious behavior (SIB) is a significant human health problem frequently associated with profound intellectual disabilities, genetic diseases, and psychiatric conditions. However, it also occurs in subclinical populations and appears to be on the rise in adolescents and young adults. SIB is also seen in a small percentage of nonhuman primates that injure themselves through biting. We have begun to characterize SIB in rhesus monkeys to identify some of the risk factors associated with this disorder, and to determine the parallels with the human condition. In our study population, 14% of individually housed monkeys (the vast majority of which are males) have a veterinary record for self-inflicted wounding. Wounding is rare, but self-directed biting is common. SIB can be elicited during aggressive altercations and may be associated with husbandry events. Some monkeys appear to be more vulnerable to acquiring SIB. This increased vulnerability is associated with certain social experiences in the first 2 years of life and with exposure to a larger number of moderately stressful events as compared to controls. Monkeys with SIB also have a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, indicated by a blunted cortisol response to mild stressors. Our findings suggest that SIB may be a coping strategy to reduce arousal. Biting appears to rapidly lower an escalating heart rate. The potentially reinforcing effects of SIB may account for the failure of some treatment regimens. These findings are compared to studies of SIB in humans, and concordances are identified.

Beta-endorphin levels in longtailed and pigtailed macaques vary by abnormal behavior rating and sex

“…In our study, male macaques were more likely to have higher abnormal behavior rank scores than females. In general, male macaques are significantly more likely than females to exhibit SIB and other serious abnormal behaviors [31,32]. Among developmentally delayed (DD) humans, SIB is slightly more prevalent in males [38].…”

“…Humans with "contagious" SIB, where bouts of SIB follow one another in rapid succession, have especially high levels of intact βE relative to ACTH [45]. Rhesus macaques with high rates of SIB have blunted cortisol responses to mild stress [31,52]. Autistic individuals, with and without SIB, have higher ACTH and lower cortisol basal levels compared to controls [12].…”

“…As a consequence, they may experience diminished psychological well-being, and the research projects in which they participate may be compromised [1,14,31,32]. Recent data [53] contribute to our understanding of the potential role of endogenous opioids in the development and maintenance of severe abnormal behavior in nonhuman primates but do not address the contribution of different βE fragments and are restricted to rhesus macaques (Macaca mulatta).…”

Refinement

“…Now, 25 years later, the body of evidence in favor of socially housing most laboratory animals has grown formidable. Building upon the work of Harlow and Harlow (1962), Novak (2003Novak ( ), lutz et al (2007, and others have further demonstrated the deleterious behavioral effects of singly housing non-human primates. Additionally, the literature has demonstrated that non-human primates are far from the only laboratory species for which social housing is important.…”

Refinements in husbandry, care and common procedures for non-human primates

“…from veterinary procedures) have been implicated in the development of self-injurious and stereotypical behaviour in rhesus macaques (Lutz et al 2003, Novak 2003. Rigid scheduling of certain animal care events, such as feeding, has also been shown to influence the expression of stereotyped behaviour in a variety of primate species (Krishnamurthy 1994, Bloomsmith & Lambert 1995.…”