Maternal factors regulate stress responsiveness in the neonatal rat

Experiment 1 compared (basal and stress-induced) adrenocortical secretion in infants individually isolated for a 24-h period with infants deprived of their mothers but in contact with their littermates. Maternal deprivation resulted in the activation of the pups’ hypothalamic-pituitaryadrenal (HPA) system, independent of the social contact with the littermates. Results from Experiment 2 showed that nonnutritional contact with a thelectomized (nipple-removed) dam was only partially effective in suppressing the HPA system activity, and this effect was age dependent. Experiment 3 explored the possibility that glucocorticoids transported through the milk might be involved in the inhibition of the HPA system. Infants that remained with an adrenalectomized dam for 24 h prior to testing did not differ from their nondeprived counterparts on Day 8 but did differ on Day 12, suggesting that, at the older ages, the nutritional demands were greater and that the effects observed were probably due to undernutrition.