OBJECTIVETo investigate the effects of preweaning enrichment on the expression of activity-regulated cytoskeletal protein (Arc), an immediate early gene, and on the long-term memory in rats.

METHODSForty neonatal Sprague-Dawley rats were randomly assigned to control group (standard environment, n=20) and experimental group (enriched environment, n=20). The experimental group received enriched environment exposure from postnatal day 10 until weaning (2 weeks, 20 minutes per day). The open field and novel object recognition tests were performed at postnatal day 28. Arc expression was detected by Western blotting and immunohistochemistry.

RESULTSThere was no significant difference in the open field test between the two groups. However, in the novel object recognition test, the experimental group rats performed significantly better than the control rats after 1 and 24-hr retention. The preference index in the experimental group after 1-hr (59.61%+/-9.61% vs 50.46%+/-9.34%; P<0.05) and 24-hr retention (62.72%+/-14.12% vs 52.39%+/-9.16%; P<0.05 ) was significantly higher than that in the control group. Arc expression in both areas CA1 and DG of hippocampus in the experimental group increased significantly compared with that in the control group (P<0.01).

CONCLUSIONSPreweaning enrichment can up-regulate the expression of immediate early gene, Arc, in the hippocampus of the rats, and promote their long-term memory.