This study aimed to explore the potential mechanism by which baicalin reduces neuroinflammation in mice with depression by regulating the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB) signaling pathway.This study employed a systematic investigation combining behavioral testing,inflammatory cytokine assays,signaling pathway protein analysis,and microglial activation observation.Sixty mice were randomly divided into the following groups:control,model,fluoxetine (10 mg/kg),and low-dose,medium-dose,and high-dose baicalin groups (50,100,200 mg/kg).Except for the control group,all other groups were modeled for depression using chronic unpredictable mild stress (CUMS).Following successful modeling,each group was given the corresponding drug intervention for 28 days.Depression-like behavior was detected by forced swimming and tail suspension test,the activation of microglia in the amygdala was detected by immunohistochemistry,the levels of tumor necrosis factor-α (TNF-α),interleukin-1β (IL-1β),and IL-6 in serum and the amygdala were detected by ELISA,and the mRNA expressions of TLR4,MyD88 and NF-κB p65 in the amygdala were detected by RT-qPCR.The expression of TLR4,MyD88,NF-κB p65 and p-NF-κB p65 protein in the amygdala were detected by Western blot.Compared with control group,mice in the model group exhibited significantly prolonged immobility times (P<0.01),the number of microglia in the amygdala was significantly increased (P<0.01),and the levels of TNF-α,IL-1β and IL-6 in serum and the amygdala were significantly elevated (P<0.01).The mRNA and protein expressions of TLR4,MyD88 and NF-κB p65 in the amygdala were significantly increased (P<0.01).Compared with model group,the immobile time of baicalein medium and high dose groups was decreased (P<0.01),and the desperate behavior of depression model mice was improved.Different doses of baicalin reduced microglial hyperactivation to varying degrees (P<0.01),decreased proinflammatory factor levels in serum and the amygdala (P<0.01),and inhibited TLR4,MyD88,NF-κB p65 mRNA,and protein expression in the amygdala (P<0.01).These findings suggest that baicalin may inhibit TLR4/MyD88/NF-κB signaling pathway activation,reduce proinflammatory factor levels in the amygdala,and suppress excessive microglial activation to alleviate neuroinflammation,thereby improving depressive-like behaviors in CUMS model mice.