Physical exercise improve social interaction induced by social‐defeated stress

Psycho‐social stress is one of the important risk factor for depression. Recent studies reported that physical exercise eases depressive behavior. But, effect of exercise on psycho‐social stress is unclear. In this study, we investigated the effect of exercise on social interaction behavior using social‐defeat stress (SDS). Male C57BL/6J mice were attacked by retired ICR mice (aggressor) for 2.5 min. After the physical interaction, aggressor and experimental mice were maintained in sensory contact for 1 hour using acryl central plate dividing the aggressor home cage in 2 halves. After sensory contact, experimental mice were transferred to another cage with (Ex) or without (St) freely accessible activity wheel for 2 hours. After then, experimental mice were housed with the same aggressor mouse resident maintained in sensory contact during stress period. We also made control (Con) or exercise (N‐Ex) group without SDS. The SDS was performed for 5 days followed by 2 days of no SDS. Two weeks later, we examined some behavioral test in mice and monoamine level in brain. St group showed negative social interaction with aggressor mice compared to Con group while Ex group did not show the negative social interaction. In contrast, N‐Ex group showed positive social interaction. There were no significant differences in other behavioral tests among these groups. We observed that exercise decreased the elevated monoamine turnover by SDS in amygdala, which is critical site for fear memory. These results suggest that physical exercise reduces the SDS‐induced social avoidance behavior with decrease of monoamine turnover in amygdala.