Enriched environment combined with fluoxetine ameliorates depression-like behaviors and hippocampal SYP expression in a rat CUS model

Abstract Effects of enriched environment (EE) combined with fluoxetine in a chronic unpredictable stress (CUS) rat model were examined in our study. Thirty male Sprague-Dawley rats were randomly divided into control group, CUS group, CUS + EE group, CUS + fluoxetine group, and CUS + EE + fluoxetine group (n = six per group). Rats in the CUS group were bred under conditions of CUS and separation for 6 weeks; Control group animals were bred in group cages (three rats per cage) under standard laboratory conditions for 6 weeks; Rats in CUS + EE group, CUS + fluoxetine group, and CUS + EE + fluoxetine groups were bred under the conditions of CUS and separation for 6 weeks and had an intervention of EE, an oral gavage of fluoxetine, and an intervention of EE + oral gavage of fluoxetine, respectively, every day for the final 3 weeks. Every rat underwent a behavioral assessment at the beginning of the 1st week, at the end of the 3rd week and at the end of the 6th week. Behavioral assessments included sucrose water consumption, weight measurement, and an open field test (measuring horizontal moving distance, rearing behavior, and defecation). Finally, the level of synaptophysin expressed in the hippocampus was measured with immunohistochemistry. We found that EE, fluoxetine, and EE + fluoxetine all reversed the depression-like behaviors of CUS rats. The effect of EE + fluoxetine appeared to be superior to EE or fluoxetine alone; the expression level of synaptophysin in CA1, CA3, and DG of the hippocampus was decreased in CUS rats, however, exposure to EE, fluoxetine, and EE + fluoxetine all reversed this decrease.