TNF and major depressive disorder: Chronic stress and the release of proinflammatory cytokines such as IL-1β, IL-6, and TNF-α lead to chronic neuroinflammation, which contributes to depression [27, 28]. IL-1β, IL-6, and TNF-α mRNA expression was significantly increased in the hippocampus of control mice, although this effect was ameliorated by treatment with GBH, FXT, and AMT (Figure 5).