TNF and major depressive disorder: However, there is only a very limited number of animal studies investigating the microglial and cytokine effects of antidepressants at the same time, e.g., the antidepressant fluoxetine did not affect the microglial activation marker IBA-1, but significantly reversed the increase in IL-1β levels induced by lipopolysaccharide and decreased the TNF-α levels, associated with behavioral changes in an animal model of major depression [62,65].