Maternal corticosterone during lactation permanently affects brain corticosteroid receptors, stress response and behaviour in rat progeny.

The long-term consequences of a physiological-range increase of maternal corticosterone during lactation were investigated on the 15-month-old progeny. The offspring of rats drinking water supplemented with corticosterone (200 microgram/ml of corticosterone hemisuccinate) from day 1 postpartum to weaning exhibited: (i) better performance in a conditioned learning test; (ii) reduction of fearfulness in two conflict situations; (iii) lower stress-induced corticosterone secretion and (iv) higher number of corticosteroid receptors in the hippocampus. The results of this study show that the effects of maternal physiological-range hypercorticosteronemia during lactation are lifelong. Moreover, these data suggest that corticosteroids, secreted during neonatal life, may constitute a factor directing the neurobiological development of the infant. In line with this hypothesis, glucocorticoid-induced early events have consequences on the behavioral and physiological status of adulthood. These consequences may be either "beneficial" or "detrimental" depending on the plasma levels of corticosterone induced by the early life occurrences, as well as on the kind of the stimulus and the developmental stage at which the neonate experiences the event. The present study demonstrates that, when the increase of corticosterone in infancy is moderate, the adult rats show reduced anxiety, improved learning and a better coping strategy to deal with stressful situations.