BDNF and major depressive disorder: These results suggest that gut dysbiosis can cause neuroinflammation and colitis by inducing the proinflammatory cytokine expression through NF-κB activation, resulting in the occurrence of depression and CSS can suppress NF-kB activation-induced gut and systemic inflammation through the alleviation of gut dysbiosis, particularly the reduction of inflammatory γ-Proteobacteria to antiinflammatory Lactobacillaceae population ratio, resulting in the alleviation of anxiety and depression by inducing BDNF expression through the suppression of IL-6 expression.