Effects of Social Isolation and an Enriched Environment on Anxious-Depressive Behavior in Rats in Normal Conditions and after Early Proinflammatory Stress

The effects of being housed in different conditions (standard, social isolation, short periods in an enriched environment) from age 1.5 months to age 3.5 months on anxious-depressive behavior in adult rats subjected to early proinflammatory stress were studied. On days 3 and 5 after birth, one group of rat pups received bacterial lipopolysaccharide (50 μg/kg, LPS group); the other received physiological saline (the PHYS group, controls). Testing at age 3–3.5 months in the open field and elevated plus maze tests showed that housing in conditions of social isolation, as compared with standard conditions, led to increased anxiety in rats and risk assessment behavior (stretch attend postures), with some reductions in movement and exploratory activity. The greatest changes after social isolation occurred in rats of the LPS group. Short-term housing in an enriched environment in rats of the PHYS group had no effect on anxiety levels, though females of the LPS group showed elevated anxiety in the open field. The sucrose preference test revealed signs of depression-like behavior in females of the LPS group after social isolation and environmental enrichment. Social isolation led to the largest increase in the blood corticosterone level after an additional stress (the forced swimming test). Thus, being subjected to early proinflammatory stress increased reactivity to adverse stress in adulthood, females being more vulnerable.