Differential effects of repeated immobilization stress in early vs. late postnatal period on stress-induced corticosterone response in adult rats

Abstract This study was performed in order to determine how immobilization stress in the early postnatal period or in the late postnatal period affects growth in the developing rat, and the response of the hypothalamus–pituitary–adrenocortical (HPA) axis in adult rats subjected to subsequent novel stresses. In addition, the effects of maternal deprivation (MD) within the same period of exposure to immobilization stress were also examined. We used two different types of immobilization stress and two different types of MD: immobilization stress for 30 min per day from postnatal day 7 (P7) to P13 (IS-E group); immobilization stress for 30 min from P15 to P21 (IS-L group); MD for 30 min per day from P7 to P13 (MD-E group); and MD for 30 min per day from P15 to P21 (MD-L group). The IS-E group showed a significant reduction in body weight that was maintained until at least P40 when compared with the control group. On the other hand, the IS-L group showed a significant reduction in body weight at only postnatal day (P) 20 when compared with the control group. Furthermore, the IS-E group showed a larger HPA response to novel stress than the IS-L and control groups in adulthood. The MD-E group showed a significant reduction in body weight that was maintained until at least P20 when compared with the control group, but did not show a larger HPA response to novel stress, except at T30 (30 min after exposure to novel stress) than the control group in adulthood. The MD-L group did not show a significant reduction in body weight or increased HPA response when compared with control rats. These results suggest that repeated immobilization stress, but not MD, in the early postnatal period induces long-term effects on growth and HPA response to novel stress in adulthood.