Abstract

Chronic stress can cause emotional dysfunction, but exposure to an enriched environment (EE) can benefit emotional homeostasis. Recent studies have demonstrated that EE can ameliorate stress-induced depressive-like behaviors. Whether hypothalamic-pituitary-adrenal (HPA) axis activity and corticosteroid receptors are involved in these effects of EE is not known. In our current study, we examined HPA axis activity and hippocampal mineralocorticoid receptor/glucocorticoid receptor (MR/GR) mRNA levels following chronic stress in rats. Our study showed that stress reduced body weight, decreased sucrose intake and sucrose preference, and increased immobility in a forced swimming test. These effects were ameliorated by EE. Also we found that 21 days of restraint stress resulted in low HPA axis activity, and a reduction of MR mRNA and MR/GR ratio in the hippocampus of rats, which was restored by EE. Thus, our current results emphasizes the efficiency of EE in the amelioration of stress-induced decrease in the mRNA expression of MR and MR/GR ratio as well as behavioral depression, providing initial evidence for a possible mechanism by which an enriched environment can restore stress-induced deficits.

Keywords: Chronic restraint stress, enriched environment, depression, HPA axis, corticosteroid receptor, emotional dysfunction, hippocampal mineralocorticoid, ameliorated, restraint stress, desensitization, habituation, corticosterone levels, homeostasis, Neurohormone Assay, antidepressant therapeutic effects