Effects of ethanol on social avoidance induced by chronic social defeat stress in mice

In rodents, chronic social defeat stress promotes deficits in social interest and social interaction. We further explored these antisocial effects by comparing the consequences of two different defeat stress protocols (episodic vs. continuous stress) in a social investigation test. We expected that continuous, but not episodic, stress would induce social deficits in this model. Furthermore, we tested whether a potentially anxiolytic dose of ethanol reverses social deficits induced by defeat stress. Male Swiss mice were exposed to a 10-day social defeat protocol, using daily confrontations with an aggressive resident mouse. Episodic stress consisted of brief defeat episodes, after which the defeated mouse was returned to its home cage, until the next defeat 24 h later (n = 7–11/group). For continuous stress, similar defeat episodes were followed by cohabitation with the aggressive resident for 24 h, separated by a perforated divider, until the following defeat (n = 8–14/group). Eight days after stress termination, defeated and control mice were assessed in a social investigation test, after treatment with ethanol (1.0 g/kg, i.p.) or 0.9% saline. Considering the time spent investigating a social target, mice exposed to episodic or continuous social stress showed less social investigation than controls (p < .05). Deficits in social interest were not reversed by acute ethanol treatment. However, ethanol reduced time spent in social interaction in one control group (p < .05). Locomotor activity was not affected by social stress or ethanol. Thus, a history of social defeat stress, whether episodic or continuous, promotes deficits in social investigation that were not reversed by acute treatment with ethanol.