Objective:Berberine,a cationic alkaloid first isolated in 1917,has been approved by the China Drug Administration for decades.Accumulating evidence demonstrated its antidepressant-like activities in vivo.Our previous study has shown that chronic stress leads to the upregulation of miR-34a in the hip-pocampus of mice.This study aims to evaluate the underlying miR-34a mediated mechanism of berber-ine in chronic stress-induced depression in mice.Methods:In the present study,mice were administered with berberine during chronic stress.Levels of miR-34a,dendritic density,mitochondrial morphology,and neurogenesis were assessed in the hip-pocampus.Subsequently,miR-34a agomir was used as a pharmacological intervention for the investiga-tion of berberine.Results:The results showed that berberine reversed the decrease in sucrose preference and the increase in latency to feed without altering total food consumption.Furthermore,chronic stress-induced overex-pression of miR-34a decreased synaptotagmin-1 and Bcl-2 levels,thereby impairing spinal morphology,mitochondria and neurogenesis.Berberine inhibited miR-34a expression,in turn restored synaptotagmin-1 and Bcl-2 levels,and thus improved spinal morphology,mitochondria and neurogenesis in the hippocampus.However,the improvements induced by berberine were totally blocked by the pre-treatment of miR-34a agomir,which caused the elevation of miR-34a levels in the hippocampus.Conclusion:This finding demonstrated that miR-34a downregulation was involved in the antidepressant-like effects of berberine in mice exposed to chronic stress.