Psychological stress and environmental adaptation in enriched vs. impoverished housed rats

In this study, we report differential behavioural and cognitive effects, as assessed in the open-field and the Morris water maze, following psychological stress in enriched vs. impoverished housed rats. Three stress conditions were evaluated: nonstress, mild stress and powerful stress. Mild stress consisted of exposure to an avoidance box but without shock, while in the powerful stress condition animals were exposed to an electric shock. The results revealed distinct effects in the differentially housed animals. Prior exposure to a mild stress enhanced escape performance in the water maze in enriched but not impoverished animals. However, preexposure to powerful stress negatively affected animals from both housing conditions in the water maze task, but with the enriched animals less affected than impoverished animals. In the open-field test, stress preexposure reduced locomotion counts in both the differentially housed animals. In addition, the results showed that the enrichment effect on emotional reactivity in the open-field is long-lasting and persists even after extensive training and housing in standard laboratory conditions. The results are discussed in relation to the nature of the behavioural and learning differences between the differentially housed animals.