Stress-induced social avoidance: a new model of stress-induced anxiety?

We have studied the long-term behavioral effects of a single stressor in male rats by using an approach/avoidance situation as the behavioral endpoint. A single exposure to social defeat or electric shocks was used as stressors. Behavioral testing was performed in a two-compartment cage divided by an opaque wall and connected by a short tunnel. The larger compartment contained an unfamiliar male rat that was separated from the rest of the compartment by a transparent, perforated Plexiglas wall. The subject was placed in the small compartment and allowed to explore the cage for 5 min. The test was performed on Days 1, 5, or 10 after stress application. Unstressed rats spent 90% of time in the large compartment that contained the unfamiliar male. Social defeat dramatically reduced the exploration of the large compartment, without time-related changes in this response. A mild electric shock had a similar effect that lasted more than 5 days but less than 10 days. The exploration of an empty cage was significantly less inhibited by stress than the exploration of a cage that contained the stimulus rat. The test could be applied repeatedly in the same rat, without major changes in the response. Chlordiazepoxide applied 1 h before behavioral testing abolished completely the stress-induced behavioral deficit. We suggest that the model can be used for studying the effects of various compounds on stress-induced anxiety.