Pro-resilient effects of environmental enrichment on social isolation: Behavioural and cytochrome c oxidase brain analysis in Wistar adult rats.

The COVID-19 pandemic has underscored the impact of social isolation on mental well-being. This study aims to evaluate the emotional and cerebral consequences of social isolation and assess whether prior environmental enrichment can mitigate the adverse effects. For that purpose, four groups were established: Behaviour group (Beh), n=8, subjected to a 4 % sucrose consumption test and the elevated zero maze (EZM) to assess anhedonia and unconditioned anxiety; Social isolation (SI) + Behaviour group, n=8, subjected to 4 consecutive weeks of social isolation followed by the behavioural testing; Environmental enrichment: EE+SI + Behaviour group, n = 8, subjected to EE prior to SI followed by behavioural assessment; and Basal group (BG), n = 8, used to determine the baseline of cytochrome c-oxidase (CCO). After behavioural testing, brain tissue from the prefrontal cortex (PFC), dorsal and ventral hippocampus (vHIP), nucleus accumbens (NAc), and ventral tegmental area (VTA) were analysed for CCO activity. Results show that SI serves as a significant stressor, increasing anxiety and anhedonic responses in the SI group. However, pre-exposure to EE significantly reduced these responses. Regarding CCO activity, the SI group exhibited elevated levels across all brain regions compared to the EE+SI group. Moreover, the EE+SI group maintained CCO activity levels similar to those of the Basal group, suggesting that prior EE exposure mitigates the metabolic impact of social isolation across most brain regions, except for the vHIP. These results indicate that pre-exposure to an EE may buffer the adverse effects of SI, supporting enhanced resilience.