Running Head: ENRICHMENT EFFECTS ON OBJECT-IN-PLACE TASK 1 Enrichment Effects on Object-in-Place Task Performance in the Adolescent Rat are Due to Task Novelty and Subject Age

Adolescence is a period of rapid physical growth, correlated with increased exploration and novelty-seeking behaviors that can be potentially risky. These behaviors can be mediated by processes such as environmental enrichment (EE), which consists of repeated exposure to novelty and physical exercise beyond that available in standard lab housing. Prior research indicates EE has a significant mitigating effect on novelty-seeking behaviors in the adolescent rat during early adolescence (pnd 36), but not late adolescence (pnd 50), in an Object-in-Place (OiP) task. Prior research also indicates there are significant sex differences at pnd 36 but not pnd 50 in OiP testing. This study elucidates whether task novelty or subject age at time of testing produced these observed differences by testing OiP once in late adolescence. The current study analyzed the CA1, DG, and CA3 regions of the hippocampus to determine processing of novelty following the OiP task, and analyzed the BLA and LA regions of the amygdala to determine potential fearlearning during the task. Behavioral results found that the main effect of enrichment was agedependent, whereas observed sex differences were task-novelty dependent. Neural analysis indicated that the CA1 and LA were significantly less active in EE subjects, but no other region was statistically different between groups. EE was found to have a beneficial impact on subjects, but that this impact was stronger in early adolescence.