Maternal contact inhibits pituitary-adrenal stress responses in preweanling rats

Three experiments examined psychological factors which inhibit pituitary-adrenal activity in 12-, 16-, and 20-day-old rats. Infant rats were placed in heated novel test arenas for 30 min--a treatment which increases corticosterone secretion--and were presented with different appetitive stimuli in order to determine whether these stimuli inhibit this increased hormone secretion. The first experiment was a factorial combination of two conditions: suckling an anesthetized dam and milk ingestion through an intraoral cannula. At all ages, suckling inhibited corticosterone secretion but milk ingestion did not, nor was there an interaction of these factors. In the second experiment, the importance of suckling was assessed by allowing pups' contact with an anesthetized dam either with or without the opportunity to suckle. At all ages, contact with suckling and contact alone were equally effective in inhibiting corticosterone secretion. The third experiment asked whether contact with a lactating female is necessary for pituitary-adrenal inhibition or whether more distal cues associated with lactation are sufficient. Pups were tested under one of four treatments formed by a 2(Lactating vs. Virgin Female) X 2(Contact vs. No Contact) factorial design. At all ages inhibition of corticosterone secretion occurred only in animals which were allowed contact with an anesthetized female. Lactating and virgin females were equally effective for the 12- and 16-day-old pups, but contact with a virgin female was less effective for the 20-day-old pups. These findings indicate that neuroendocrine mechanisms subserving inhibition of the pituitary-adrenal system exist during the preweanling period in the rat, and suggest the possibility of maternal regulation of this physiological system during development.