Despite the recognized roles of neuroinflammation in mental illnesses, PET imaging on currently available biomarkers has limitations due to the lack of evidence demonstrating their relationship to the molecular and cellular events of inflammation associated with the pathology of mental illness. Rodent stress models, such as chronic social defeat stress (SDS), have identified crucial roles for COX-1 and TLR4, which are innate immune molecules, in chronic SDS-induced neuroinflammation and its behavioral consequences. In this study, we performed COX-1 and TLR4 PET imaging at multiple time points during chronic SDS in mice. For COX-1 PET imaging, we used the COX-1 PET probe (S)-[