Social Defeat Stress Induces Depression-like Behaviors in Adolescent C57BL/6 Mice

Exposure to stress is highly correlated with the emergence of mood-related psychopathologies, such as general anxiety and major depressive disorder. Because the first episode of major depression often emerges in adolescence, we investigated the effects of chronic social defeat stress on responses to emotion-eliciting stimuli in juvenile mice. Specifically, postnatal day (PD) 35 male C57BL/6 mice were exposed to 10-minute episodes of social defeat stress for 10 consecutive days (PD35-44), while control mice were handled daily. Twenty-four hours after the last episode of stress (PD45), separate groups of mice were tested on a battery of emotion-eliciting tests, including the social interaction-, forced swim-, and sucrose preference-test. Defeated adolescent mice exhibited a depression-like phenotype as inferred from increased avoidance behavior in the social interaction test, increased time spent immobile in the forced swim test, and a lower preference for a sucrose solution ( a measure of anhedonia), when compared to non-defeated controls. In general, we show that exposure too social defeat stress during adolescence induces a depression-like behavioral phenotype in C57BL/6 mice. Thus, our findings suggest that the social defeat paradigm may be used as a model to examine the emergence of stress-induced mood-related disorders during the adolescent stage of development