Stress-induced escalation of alcohol self-administration, anxiety-like behavior, and elevated amygdala Avp expression in a susceptible subpopulation of rats.

Comorbidity between alcohol use and anxiety disorders is associated with more severe symptoms and poorer treatment outcomes than either of the conditions alone. There is a well-known link between stress and the development of these disorders, with post-traumatic stress disorder as a prototypic example. Post-traumatic stress disorder can arise as a consequence of experiencing traumatic events firsthand and also after witnessing them. Here, we used a model of social defeat and witness stress in rats, to study shared mechanisms of stress-induced anxiety-like behavior and escalated alcohol self-administration. Similar to what is observed clinically, we found considerable individual differences in susceptibility and resilience to the stress. Both among defeated and witness rats, we found a subpopulation in which exposure was followed by emergence of increased anxiety-like behavior and escalation of alcohol self-administration. We then profiled gene expression in tissue from the amygdala, a key brain region in the regulation of stress, alcohol use, and anxiety disorders. When comparing "comorbid" and resilient socially defeated rats, we identified a strong upregulation of vasopressin and oxytocin, and this correlated positively with the magnitude of the alcohol self-administration and anxiety-like behavior. A similar trend was observed in comorbid witness rats. Together, our findings provide novel insights into molecular mechanisms underpinning the comorbidity of escalated alcohol self-administration and anxiety-like behavior.