The effects of stress and environmental enrichment on cognitive functions and stress-related gene expressions in the brain of aged rats

We aimed to investigate whether environmental enrichment (EE) would alter possible adverse effects of chronic unpredictable mild stress (CUMS) in elderly rats regarding corticosterone levels, stress-related gene expressions in some brain regions, and learning and memory. Wistar male rats (over 20 months) weighing 450-550 g were housed in enriched or standard cages for the duration of the study (10 weeks). After 8 weeks of CUMS application, body weight gain, adrenal weight, and corticosterone levels were measured. Morris water maze (MWM), and novel object recognition test were performed. Glucocorticoid receptor (GR), corticotropin-releasing hormone (CRH), and corticotropin-releasing hormone receptor 1 (CRHR1) expression levels were determined in the hypothalamus and hippocampus. In the stress group, body weights decreased over time. Regarding the distance swum by rats to find the platform in the MWM, while there was no significant difference between the 3rd and 4th days in the EE+CUMS group, the decrease continued until the 4th day in the standard control (SC)+CUMS group. Stress application reduced the GR and CRHR1 gene expressions in the hypothalamus. We conclude that chronic stress and EE caused brain region-specific changes, thus affecting the neurobiological and cognitive functions in the elderly. In this respect, our study will contribute to neurobiological and neurodegenerative studies on aging.