Long-term effects of differential early rearing in rhesus macaques: behavioral reactivity in adulthood.

Adverse early experiences are associated with a range of deleterious health outcomes in humans, including higher risk for affective disorders. Studies using a long-standing model of nonhuman primate model of early adversity have demonstrated that nursery-reared (NR) monkeys exhibit alterations in multiple aspects of biobehavioral development; however, few studies have evaluated the persistence of socioaffective behavioral changes through adulthood. We evaluated the effects of early rearing experience on adult animals' response to a well-validated assessment of anxiety-like behavior, the human intruder paradigm (HIP). We tested 22 rhesus monkeys who were either nursery-reared (NR) or reared with their mothers (mother-reared; MR). NR monkeys were inhibited in their behavior compared to MR monkeys, with reduced locomotion and exploratory behaviors. NR animals showed a marginal increase in freezing. Together these findings demonstrate that the consequences of differential infant rearing experience on socioaffective behavior persist into adulthood, with evidence of greater inhibition in NR monkeys.