Maternal touch and feed as critical regulators of behavioral and stress responses in the offspring.

For half a century, Seymour Levine's pioneering work on the interactions between mother and infant have helped us understand the critical early factors that shape physiology and behavior in the adult offspring. The work from my laboratory described in this review was based on many experiments by Levine and coworkers demonstrating that the quantity and quality of maternal milk and of maternal-infant contact influence different aspects of the hypothalamus-pituitary-adrenal (HPA) activity in the neonate. We have extended this work by showing that maternal high-fat feeding during the prenatal and lactational period blunts stress responsiveness in neonatal pups, in part mediated by increased circulating leptin levels in the offspring. The blunting of stress responses during this specific neonatal period might be beneficial to prevent the negative effects of exaggerated glucocorticoid secretion on the developing brain. In line with Levine's previous work, we found that maternal licking of the pups reduced stress responsiveness and inflammation in pups subjected to modest repeated pain during the first weeks of life and that it also blunted adult sensitivity to thermal pain. These studies have important implications for human infants as mechanisms aimed at reducing stress responsiveness can be considered protective to the developing brain from exaggerated and untimely neuroendocrine and sympathetic stimulation. Non-invasive interventions targeted at maternal nutrition and maternal care are relatively easy to implement and might have a significant effect on the health outcome of the offspring, particularly in a vulnerable population of term and pre-term babies.