Environmental enrichment modulates hormonal and behavioral responses induced by chronic stress in rats

Abstract

The aim of this study was to evaluate the effect of 2h daily exposition to environmental enrichment (EE) during 5 weeks on hormonal and behavioral responses induced by chronic mild and unpredictable stress (CMS) applied during 3 consecutive weeks in rats. Male adult rats were divided into 4 groups: control (C), EE, CMS and CMS + EE. Depression‐like behavior was evaluated in the forced swimming test (FST) and memory was evaluated by Y‐maze test at the end of protocol. One day after behavioral tests, the animals were killed and trunk blood was collected for corticosterone assay. All procedures were approved by Institutional Ethics Committee. Two‐way ANOVA + Tukey test was used, p<0.05. CMS (50.8 ± 6.1) and CMS + EE (18.0 ± 5.1) groups presented higher corticosterone plasma levels (ng/ml) compared to C (2.0 ± 0.7) and EE (2.8 ± 0.9) respectively, and CMS+EE group showed lower plasma corticosterone in comparison with group CMS. In the FST, CMS (187 ± 14) presented higher immobility (s) compared with C (123 ± 9), EE (129 ± 14) and CMS + EE (138 ± 6) groups. In the Y‐maze test the difference scores of entries (%) were lower in the CMS (1 ± 3) and CMS + EE (16 ± 5) compared to C (15 ± 3) and EE (28 ± 5) respectively. EE and CMS + EE showed increased entries difference score compared with C and CMS respectively. EE reduced corticosterone release, canceled the depression‐like behavior and the impairment of memory induced by CMS showing its protective effect.