Effects of Enriched Environment (EE) on Depressive-Like Behavior and Hippocampal Structure in Rat Model of Chronic Stress


Chronic stress is associated with the development of depression. It can trigger structural and neurobehavioral changes in the brain and has been shown to induce depressivelike behavior in animals. An enriched environment can modulate the structure and function of the brain by altering the expression of various genes and proteins as well as affecting neurotransmitters’ activity. The hippocampus plays an important role in
controlling the networks for mood regulation and has been implicated in the course of depression. This study aimed to investigate the effect of an enriched environment on the depressive-like behavior and hippocampal structure in rats after unpredictable chronic mild stress (UCMS) exposure. Male Wistar rats (Rattus novergicus) were divided into three groups, each consisting of 6 rats including the control, UCMS and UCMS+EE
group. Unpredictable chronic mild stress and EE were given for 21 days. Body weight gain, depressive-like behavior, and hippocampal structure were evaluated at the end of the experiment. Depressive-like behavior was assessed with Forced Swim Test (FST) and Sucrose Preference Test (SPT). Thickness of the pyramidal layer of CA1 and CA3 area were measured with histologic examination to see changes in the hippocampal
structure. Data were analyzed using One-Way ANOVA or Kruskal-Wallis followed by multiple comparison post hoc test. The enriched environment could significantly maintain body weight gain (p = 0.036) and rat’s preference to sucrose solution (p =0.001) in a stressful condition. Enriched environment reduced immobility time in FST but it was not statistically significant (p = 0.177). There was a significant difference in the thickness of CA1 and CA3 pyramidal layer of the hippocampus among groups (p=0.015 and p=0.019 respectively). Stress markedly decreased the thickness of CA1 and CA3 pyramidal layer (p=0.014 and 0.011 respectively). The enriched environment can ameliorate stress-induced depressive-like behavior and alteration in hippocampal
structure in rats.

Keywords: Environmental enrichment, depression, stress, hippocampus

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