The differential effects of brief environmental enrichment following social isolation in rats

Environmental enrichment (EE) in rodents is associated with a wide range of physiological, affective, and cognitive benefits. A seemingly opposite housing condition, social isolation (SI), is used as a rodent model of stress, negatively affecting several neurobiological mechanisms and hampering cognitive performance. Experimental designs that involve switching between these housing conditions produced mixed results. We evaluated different behavioral and cognitive effects of brief EE following long-term, SI-induced stress. We revealed the influence of enrichment after 30 days of isolation on behavioral despair, anxiety-like behavior, and spatial working memory in adult male Wistar rats and found a substantial anxiolytic effect in the experimental (SI to EE) group. Interestingly, rats exposed to EE also showed increased behavioral despair compared with the control (continuous SI) group. There was no difference in spatial working memory performance at the end of a 5-day water Y-maze (WYM) test. However, the SI to EE animals displayed better memory performance in the first 2 days of the WYM, indicating faster learning. In line with this difference, we recorded significantly more c-Fos-immunopositive (c-Fos+) cells in the retrosplenial and perirhinal cortices of the SI to EE animals. The lateral and basolateral nuclei of the amygdala showed no such difference. These results suggest that brief enrichment following isolation stress leads to differential results in affective and cognitive systems.