Psychiatric disorders now comprise a significant health and financial burden in the US, costing billions in lost production and wages. Two of the more prevalent psychiatric disorders, depression and addiction, affect millions of adults, and current therapeutic options offer limited relief. Despite the prevalence of these disorders, little is known about their underlying mechanisms. Part of the difficulty in studying the etiology of psychiatric diseases is the dearth of animal models for human disorders such as depression. Recent work has utilized a chronic social defeat model in mice that induces symptoms relevant to depression and posttraumatic stress disorder. Using this model, the importance of the mesocorticolimbic dopamine (DA) system has been revealed. This pathway consists of DA neurons in ventral tegmental area (VTA) that project to the nucleus accumbens and prefrontal cortex
