MPO and major depressive disorder: FR transplantation significanlty increased anxiety- and depression-like behaviors, IL-6 expression in the hippocampsus, IL-6 and corticosterone levels in the blood, TNF-α and IL-6 expression, myeloperoxidase activity, and NF-κB activation (p-p65 to p65 ratio) in the colon, while the FN transplantation did not significantly affect them (Fig. 4E–M).