EFFECTS OF MATERNAL-DEPRIVATION ON THE ACTH STRESS RESPONSE IN THE INFANT RAT

Prolonged maternal deprivation during early ontogeny results in increa sed basal and stress-induced corticosterone levels. In the following e xperiments we examined whether these increases were due, at least in p art, to augmented ACTH secretion. Thus, ACTH levels were measured in 2 4-hour maternally deprived and nondeprived 6-, 9-, and 12-day-old pups exposed to a mild stressor (i.e. saline injection followed by placeme nt in a novel environment at room temperature). The results showed: (1 ) nondeprived pups showed a small response to saline - the response of deprived pups, however, was greater than that of nondeprived pups; (2 ) the magnitude of the response increased with age; (3) ACTH levels re mained elevated for at least 30 min. Subsequent experiments examined w hether the continuous exposure to novelty and/or loss of body heat cou ld explain the persistence of this response. Neither variable affected the ACTH response to saline. Our results indicate that factors of mat ernal origin are partly responsible for the regulation of the ACTH res ponse to stress. Furthermore, the persistence of the response suggests that the negative feedback system in the infant is immature.