Within-litter variation in maternal care received by individual pups correlates with adolescent social play behavior in male rats.

Maternal care represents an essential environmental factor during the first post-natal week(s) of rodents and is known to have lasting consequences for neuronal structure, brain function as well as behavioral outcome later in life, including social functions and reward-related processes. Previous experiments have shown that the amount of maternal care received by individual pups varies substantially, even within one litter. During adolescence, mammals display high levels of social play behavior, a rewarding form of social interaction that is of great importance for social and cognitive development. In order to investigate how maternal care influences adaptive social behavior later in life, we here examined whether individual differences in maternal licking and grooming (%LG) received during the first postnatal week affect social play behavior during adolescence. We observed that %LG received by male rats early in life correlates positively with the frequency and duration of pouncing and pinning, the two most characteristic behavioral expressions of social play behavior in rats. The latency to engage in social exploration also correlated with %LG. In female rats we observed no correlation between %LG and any social parameter. The data indicate that subtle variations in maternal care received early in life influence social interactions in male adolescent rats. These changes in social play likely have repercussions for the social development of male rats, suggesting that maternal care can have both direct and indirect effects on the behavioral development of the offspring.

Maternal care received by individual pups correlates with adult CA1 dendritic morphology and synaptic plasticity in a sex-dependent manner.

Maternal care is an important environmental factor for rats early in life. Adult offspring from dams exhibiting extremely high versus low maternal care differ remarkably in dendritic complexity and long-term synaptic potentiation in the CA1 area. However, >70% of the pups do not belong to these extreme categories of maternal care, questioning the general relevance of these observations. Therefore, the present study investigated whether the influence of maternal care is discernable over its entire range and can serve as an index predicting later CA1 structure and function. The amount of licking and grooming (%LG) received was determined for each pup during the first postnatal week. In males, both total apical branch length and dendritic complexity correlated significantly and positively with %LG. In females, we observed a nonsignificant negative correlation, also when controlled for variations in oestradiol and progesterone levels. The correlation in females was significantly different from that in males. No significant correlation was observed between the %LG and the amount of synaptic potentiation, either in male or in female offspring, regardless of whether slices had been treated with corticosterone or vehicle. However, in male rats, the degree of potentiation seen after corticosterone compared to vehicle treatment was almost significantly related to the %LG received early in life; this differed significantly from that observed in females. The data from the present study suggest that %LG received early in life results in mild, yet sex-dependent effects on adult CA1 structure and function.