Enriched environment restores hippocampal cell proliferation and ameliorates cognitive deficits in chronically stressed rats

Abstract

Adult neurogenesis, particularly in the subgranular zone, is thought to be linked with learning and memory. Chronic stress inhibits adult hippocampal neurogenesis and also impairs learning and memory. On the other hand, exposure to enriched environment (EE) is reported to enhance the survival of new neurons and improve cognition. Accordingly, in the present study, we examined whether short-term EE after stress could ameliorate the stress-induced decrease in hippocampal cell proliferation and impairment in radial arm maze learning. After restraint stress (6 hr/day, 21 days) adult rats were exposed to EE (6 hr/day, 10 days). We observed that chronic restraint stress severely affected formation of new cells and learning. Stressed rats showed a significant decrease (70%) in the number of BrdU (5-bromo-2'-deoxyuridine)-immunoreactive cells and impairment in the performance of the partially baited radial arm maze task. Interestingly, EE after stress completely restored the hippocampal cell proliferation. On par with the restoration of hippocampal cytogenesis, short-term EE after stress resulted in a significant increase in percentage correct choices and a decrease in the number of reference memory errors compared with the stressed animals. Also, EE per se significantly increased the cell proliferation compared with controls. Furthermore, stress significantly reduced the hippocampal volume that was reversed after EE. Our observations demonstrate that short-term EE completely ameliorates the stress-induced decrease in cell proliferation and learning deficit, thus demonstrating the efficiency of rehabilitation in reversal of stress-induced deficits and suggesting a probable role of newly formed cells in the effects of EE.

Effect of environmental enrichment exposure on neuronal morphology of streptozotocin-induced diabetic and stressed rat hippocampus

“…[36,37] EE exposure assists in the survival of brain networks by accelerating synaptogenesis, axon sprouting, [38][39][40] and helps in the survival and differentiation of newborn cells of stressed rat hippocampus. [41] In a study by Beauquis et al (2010), 10 days of EE exposure to diabetic mice resulted in increased neurogenesis, vascular network, and dendritic complexity in the hippocampus. [42] Relief from uncontrolled diabetes and stressors is thought to be absolutely necessary in order to improve the overall condition of hippocampal neurons.…”

Adult Neurogenesis and Mental Illness

“…Another experimental manipulation used to bolster the proliferation and survival of new neurons in the adult dentate gyrus is enrichment of the animals' housing environment through the addition of toys, tunnels, greater space, social interactions, and other means to make home cages more complicated and stimulating (Kempermann et al, 1997;van Praag et al, 1999;Veena et al, 2009a). These environmental enrichments also reduce anxiety-, depressive-, and schizophrenic-related behaviors in animal models of illness (Jha et al, 2011;McOmish et al, 2008;Veena et al, 2009b).…”

Vascular Endothelial Growth Factor-dependent Spinogenesis Underlies Antidepressant-like Effects of Enriched Environment

“…There is evidence that adult hippocampal neurogenesis, dendritic complexity of hippocampal neurons, and some learning abilities can be improved by housing animals in EE (22)(23)(24). Moreover, long term exposure to EE has been shown to produce antidepressant-like effects in rodent models of depression (25,26). However, the molecular mechanisms underlying the effects of EE and the question of whether short term exposure to EE might also produce antidepressant-like effects remain unexplored.…”