Chronic Unpredictable Stress Impairs Social Behaviour in Adult Male Rats: Correlations with Dopamine and Serotonin Levels.

Exposure to unpredictable chronic stress has a significant impact on physical and mental health. We have previously reported that a chronic unpredictable movement restraint (CUMR) paradigm increased immobility in the forced swim test and hippocampal pro-inflammatory cytokines. In the present study, we assessed CUMR impact on social motivation and neurobiological underpinnings. Adult male rats were grouped as either control or CUMR and subjected to 2, 4, or 6 h of restraint/day for 3 weeks. Thereafter, social behaviours (social investigation and social interaction) and synaptophysin, serotonin, and dopamine levels were assessed in several brain areas. We found that CUMR-exposed animals displayed reduced body weight gain, less investigation of an unknown rat, and increased dominant behaviour. In addition, CUMR exposure reduced serotonin levels in the hippocampus and augmented dopamine levels in the amygdala and hypothalamus and serotonin turnover in the amygdala than non-stressed rats. Hippocampal serotonin was positively correlated, whereas serotonin levels in the amygdala were negatively correlated with social behaviour. Dominant behaviour was positively correlated with dopamine levels in the hypothalamus. These results indicate that CUMR impairs social behaviour, which may be explained by changes in serotonin and dopamine levels in specific brain areas.