Objective To investigate the effect and mechanism of emodin on focal cerebral ischemia in rats based on myeloid differentiation factor 88(MyD88)/extracellular signal-regulated kinase(ERK)pathway and nuclear factor-κB(NF-κB)nuclear translocation.Methods SD rats were randomly divided into sham operation group,model group and emodin group,with six rats in each group.The rat model of transient middle cerebral artery occlusion(tMCAO)was established by middle cerebral artery embolization.Rats in the emodin group were given 40 mg·kg-1 emodin by gavage for three times at 72,48 and 24 hours before modeling.At 24 hours after modeling,the neurological function of rats was scored.TTC staining was used to detect the area of cerebral infarction.HE staining was used to observe the morphological changes of brain tissue.The mRNA expression levels of MyD88 and tumor necrosis factor-α(TNF-α)in brain tissue were detected by RT-qPCR.The expression levels of MyD88,ERK,p-ERK and TNF-α in brain tissue were detected by Western Blot.The protein expression of NF-κB in brain tissue was detected by immunofluorescence.Results Compared with the sham operation group,the neurological function score of the model group was significantly increased(P＜0.01),and the cerebral infarction area was significantly increased(P＜0.01).In the cortical area of the ischemic penumbra,cell necrosis,abnormal cell morphology,nuclear fragmentation and atrophy,and the number of cells decreased significantly;the mRNA expression levels of MyD88 and TNF-α in brain tissue were significantly increased(P＜0.01,P＜0.001),the protein levels of MyD88,p-ERK/ERK and TNF-α were significantly increased(P＜0.05,P＜0.01,P＜0.001),and the proportion of NF-κB into nuclear cells was significantly increased(P＜0.001).Compared with the model group,the neurological function score of rats in the emodin group was significantly decreased(P＜0.05),and the area of cerebral infarction was significantly reduced(P＜0.05).The number and morphology of neurons in the ischemic penumbra cortex were restored to a certain extent.The mRNA expression levels of MyD88 and TNF-α in brain tissue were significantly decreased(P＜0.05,P＜0.01),the protein levels of MyD88,p-ERK/ERK and TNF-α were significantly decreased(P＜0.05),and the proportion of NF-κB into nuclear cells was significantly decreased(P＜0.001).Conclusion Emodin has a preventive and protective effect on rats with focal cerebral ischemia,which may be related to its inhibition of MyD88 activation,ERK phosphorylation and NF-κB nuclear translocation,and then down-regulation of inflammatory cascades and secretion of pro-inflammatory factors such as TNF-α,thereby exerting anti-inflammatory effects.