AIF1 and major depressive disorder: In this research, our aim is to evaluate microglial activation and hippocampal neuro-inflammation in a chronic mild stress (CMS)-induced depression model, by using a combinatory approach of in vivo [18F] DPA-714 PET imaging, ionized calcium-binding adapter molecule 1 (Iba-1) and TSPO immunohistochemistry, and detection of NLRP3 inflammasome and some inflammatory mediators.