TSPO and major depressive disorder: In agreement with findings that severe affective and behavioral dysfunction were associated with hippocampal dysfunction, the results of the Pearson correlation test in this study showed that the depression-like behavior parameters, including the first-minute activity in OFT and the immobility time in FST and TST, were all closely related to changes in hippocampal TSPO expression in the micro-PET imaging, implying the importance of immuno-inflammatory mechanism in the induction of depression-like behavior in hypothyroid rodents.