Environmental Enrichment Affects the Behavior of Adolescent Rats in a Social Preference Task

While the behavioral development of male and female rats differs, adolescents of both sexes have an interest in novelty. Environmental enrichment (EE) can add to that interest by providing opportunity for interaction with objects and other rats, and a history of EE does affect the behavior of adolescent rats in object and environment novelty preference tasks. Of interest in this study was determining if interest in social novelty might be enhanced by EE and influence adolescent rats’ interaction with a known and novel conspecific in a social preference task. On postnatal day (PND) 21, a group of rats began EE sessions with novel social partners and objects 5 days a week for 1.5 h, which continued until PND 49. On PND 35 and 49, the rats were introduced to two conspecifics, j1 and j2, for a 3-min trial, then were placed back in their home cage. After a 30-min delay, the test animals were replaced in the apparatus for a choice trial, where they were expected to show higher investigation behaviors toward a third animal, j3, rather than one of the original animals, j1. There were no significant differences between EE and no-EE animals in time spent near or nose pokes directed toward the novel animal (j3) during the test phase nor between behavior of males and females, independent of EE status. On PND 35, no-EE females investigated the third rat, j3, significantly less than the other animals. There were no differences in behavior due to main effects of EE or sex for the general investigation variables rearing or self-grooming; however, EE animals groomed more in response to novelty on PND 49 than no-EE animals, and males reared more on PND 35 and females more on PND 49. While many hypotheses were not supported, EE was an important factor and interacted with other variables to alter experimental rats’ behavior in the social preference task.