Maternal separation, which can lead to hypothalamic pituitary adrenal axis dysfunction and behavioral abnormalities in rhesus monkeys, is frequently used as a model of early adversity. Whether this deleterious effect on monkeys is reversible by later social experience is unknown. In this study, Feng and colleagues measured basal hair cortisol in rhesus monkeys after 1.5 and 3 years of normal social life following an early separation. Monkeys with maternal separation had significantly lower basal hair cortisol levels than the mother-reared monkeys at both 1.5 and 3 year time points. In addition, after 3 years of normal social life, abnormal behavioral patterns were identified in the peer-reared monkeys. The authors suggest that the deleterious effects of maternal separation on rhesus monkeys cannot be compensated by a later normal social life, indicating that the effects are long-lasting. They also suggest that the maternal-separated rhesus monkeys are a good animal model to study early adversity and to investigate the development of psychiatric disorders induced by exposure to early adversity.

Feng X, et al. Maternal separation produces lasting changes in cortisol and behavior in rhesus monkeys.
Proc. Natl. Acad. Sci. USA [Epub ahead of print, August 15, 2011]; doi: 10.1073/pnas.1010943108 .
http://www.pnas.org/content/early/2011/08/12/1010943108.abstract