IDO1 and major depressive disorder: Anti-inflammatory Lipopolysaccharide (LPS)-induced depression models demonstrated that XYW restored 5-HT levels and reduced indoleamine 2,3-dioxygenase (IDO) expression by activating the NGF/BDNF-TrkA/TrkB-CREB signaling pathway, thereby alleviating neuroinflammation and promoting neuronal survival [71].