Exposure to enriched environment restores the survival and differentiation of new born cells in the hippocampus and ameliorates depressive symptoms in chronically stressed rats

Chronic stress decreases neurogenesis in the adult brain, while exposure to enriched environment (EE) increases it. Recent studies demonstrate the ability of EE to ameliorate stress-induced behavioral deficits. Whether a restored neurogenesis contributes to these effects of EE is unknown. Recently, we demonstrated that EE following restraint stress restores cell proliferation in the dentate gyrus (DG), hippocampal volume and learning. In the current study, we examine the effects of EE following stress on survival and differentiation of the progenitor cells in the DG and behavioral depression using the forced swim test (FST) and sucrose consumption test (SCT). Adult male Wistar rats were subjected to 21 days of restraint stress followed by housing in either standard or enriched conditions (10 days, 6 h/day). Survival and differentiation of BrdU-labeled cells were evaluated 31 days post-BrdU administration. Stress decreased the survival and differentiation of progenitor cells, which was ameliorated by EE. Also the percentage of BrdU-ir cells that did not co-localize with NeuN or S100β was significantly greater in the stressed rats and was restored by EE. Stress increased immobility in FST and decreased sucrose preference in the SCT, and these behaviors were ameliorated by EE. Adult neurogenesis is thought to be linked to learning and memory and in mediating antidepressant effect. Taken together with our earlier report that EE restores stress-induced impairment in learning and cytogenesis, the current results indicate that the reversal of adult neurogenesis could be one of the mechanisms involved in the amelioration of stress-induced deficits.