Effects of early rearing conditions on cognitive performance in prepubescent male and female rats

The interactions between a mother and her offspring during early postnatal life impact cognitive development in altricial species. The current study examined the influence of postnatal rearing conditions on subsequent cognitive functioning in male and female Long-Evans rats prior to puberty. Maternal conditions were manipulated by repeated separations of rat pups from their dams on postnatal days 2 though 14. In the early handling condition, pups were removed from mothers briefly for 15 min daily, while in the maternal separation condition pups were separated from their mothers for 180 min daily. Offspring from handled or separated litters were evaluated prior to puberty between days 25–36 of life on a battery of cognitive tasks that assessed several types of memory. Male rats separated from mothers for 180 min were impaired in their non-spatial and spatial memory compared to early-handled males as indicated by their performance on an object recognition task, a Y-maze task, and reference and working memory versions of the water maze task. In contrast, maternally-separated females were not impaired, and in some cases performed better on memory tasks, compared to early-handled females. Results indicate that the biological sex of offspring moderated the effects of maternal conditions on diverse cognitive tasks. Because sex differences were evident prior to puberty, gonadal hormones likely had a limited influence on cognition. Although the bases for sex differences in the cognitive response to rearing conditions are unknown, disparities in maternal attentiveness directed toward male and female offspring may play a role.