Modern society exposes us to social and environmental stress. Acute stress activates the sympathetic nervous and neuroendocrine systems as a survival mechanism. However, chronic stress is a risk factor for mental illnesses and induces behavioral changes such as social avoidance and elevated anxiety. 
Since several groups reported that inflammatory cytokines are increased in the peripheral blood from depressive patients, we are studying the role of inflammation in chronic stress-induced behavioral changes. We previously reported that acute stress activates mesocortical dopaminergic pathway to inhibit the induction of social avoidance. On the other hand, chronic stress suppresses this pathway by the inflammatory molecule to induce social avoidance. This finding suggests that repeated exposure to stress causes inflammation. Consistently, chronic stress activates microglia, an immune cell in the central nervous system, faster than acute stress.
I will show that chronic stress induces neuroinflammation originating from microglia and this inflammation plays a crucial role in behavioral changes in this symposium. Furthermore, I'd like to introduce our latest finding.