The long-term psychobiological consequences of intermittent postnatal separation in the squirrel monkey

Long-term effects of early experiences have been well documented in rodents, non-human primates and humans. The influence of early experiences on the regulation of the hypothalamic-pituitary-adrenal has demonstrated that this biological system is highly plastic and is permanently modified by early experiences. The effects of brief periods of maternal separation in rodents tend to result in a reduction of the stress response, whereas longer periods of maternal separation produce an animal that is hyperresponsive. The effect of disruptions of mother-infant interactions on the HPA axis in non-human primates has not been clearly established. However, the primate research has primarily focused on more permanent separation paradigms and thus it is difficult to compare the rodent studies with those conducted in primates. The present study attempted to use a separation procedure in monkeys that more closely resembled the rodent model. Intermittent separation during infancy followed by reunion with the mother were shown to lead to a significant reduction in both the cortisol response and the response of the noradrenergic system following social isolation in juvenile squirrel monkeys at 2 and 3 years of age. The behavioral response (vocalizations) was also reduced.