Maternal regulation of the adrenocortical response in preweanling rats

In the following studies, we investigated the effects of 24-h maternal deprivation on the infant's hypothalamic-pituitary-adrenal system. Experiment 1 examined the effect of deprivation on the infant's corticosterone (CORT) response to adrenocorticotropin hormone (ACTH) injection. At all ages studied, deprivation resulted in a potentiation of the response. At some ages, deprived nontreated pups had higher CORT levels than nondeprived pups. Experiment 2 examined the ontogeny of the deprivation-induced stress response, and the capacity of the mother to inhibit it. From 8 days of age onwards, deprived animals showed a CORT response to saline injection that was either absent or far smaller in nondeprived pups. Saline-induced CORT secretion was diminished, or prevented, by returning the infant to its dam. Maternal reunion had no effect on ACTH-induced CORT elevations. Finally, Experiment 3 investigated the effects of deprivation over a more extended period of time. In maternally deprived pups, ACTH-induced CORT elevations persisted for at least 2 h following reunion, but by 6 h had returned to baseline. These data suggest that maternal factors are involved in the regulation of the responsiveness of the pup's hypothalamic-pituitary-adrenal system.