Effects of environmental enrichment during adolescence on social defeat effects.

Social defeat (SD) is a well established model that increases addiction vulnerability accompanied by depressive- and anxiety-like behaviors. Environmental enrichment (EE) has been shown to enhance resilience and mitigate stress-induced behavioral alterations. Here, we investigated the protective effects of EE during adolescence, both before and during SD encounters, on stress-induced anxiety, depression and the increased conditioned rewarding effects of a subthreshold cocaine dose in adulthood. We employed the social interaction test (SIT) to categorize mice into resilient and susceptible phenotypes based on depressive-like behaviors. Anxiety was assessed using the elevated plus maze (EPM). EE did not alter the percentage of resilient and susceptible mice (33%-63% in standard housing vs. 46%-54% in EE), nor did it prevent stress-induced anxiety. Only defeated mice housed under standard conditions developed 1.5 mg/kg cocaine-induced conditioned place preference, whereas EE-exposed stressed mice did not acquire cocaine-induced conditioned place preference. Our findings highlight that EE during adolescence serves as a protective factor by promoting the development of a resilient phenotype in adulthood against increased drug reward. However, it was ineffective in counteracting depressive- and anxiety-like behaviors. (PsycInfo Database Record (c) 2026 APA, all rights reserved).