In models of chronic unpredictable mild stress (CUMS) combined with corticosterone exposure, upregulation of TLR9 in the medial prefrontal cortex is associated with depressive and anxiety-like behaviors, whereas inhibition of TLR9 signaling by blocking cell-free mitochondrial DNA (cf-mtDNA) markedly attenuates stress-induced social behavioral deficits [138,139]. Here, TLR9 is linked to Anxiety.