Maternal exposure to low levels of corticosterone during lactation increases social play behavior in rat adolescent offspring.

Although costly in energy and time, social play is present and evolutionarily conserved in nearly all young mammals. Ontogenetic factors responsible for this particular form of supposed rewarding behavior are incompletely understood. Here, we have focused our attention on maternal glucocorticoid hormone. We used a model in which neonate rats are fed by mothers in which drinking water has been supplemented with 0.2 mg/ml corticosterone. The control groups were lactated by water-drinking mothers. Both male and female adolescent offspring of corticosterone (CORT) supplemented dams (CORT-nursed) showed an increase in social play behavior (i.e., pinning, pouncing, wrestling/boxing and social exploration) when compared to controls. No differences were observed between CORT-nursed progeny of both sexes and controls in the exploration of the arena during the social encounter. Finally, no differences were found in CORT plasma levels in basal conditions and following a social play session in both male and female CORT-nursed rats. These results indicate that variations in the maternal glucocorticoid status are able, directly or indirectly, to influence social play behavior in the offspring, although there is no direct relationship between the level of social play behavior and the intensity of adrenocortical activation.