Enhanced novelty-seeking after early adolescent exposure to vicarious social defeat predicts the vulnerability of female mice to cocaine reward.

Stressful experiences can have a serious impact on adolescents, as the process of brain maturation, particularly of the prefrontal cortex, takes place during this developmental period. In animal models, male mice exposed to social defeat during early or late adolescence show increased vulnerability to cocaine reward, but this effect has only been studied in late adolescent female mice exposed to Vicarious Intermittent Social Defeat (VISD). The aim of the present study was to investigate the biochemical and behavioural effects of exposure to VISD during early adolescence in female mice. VISD only induced anxiety-like symptoms in the elevated plus maze (EPM) and increased novelty-seeking behaviour in the hole-board test. Furthermore, the behavioural profile of VISD-exposed mice in these tests was associated with their vulnerability or resilience to cocaine reward in adulthood. Female mice that exhibited a higher frequency of entries in the closed arms of the EPM and a lower latency of dips in the hole-board subsequently acquired cocaine-induced conditioned place preference. Thus, exposure of female mice to VISD during early adolescence also induced short-term changes that increased sensitivity to cocaine reward in susceptible individuals.