OBJECTIVE: To study the influence of micro ribonucleic acid (miR)-155 on depression-like behaviors of depression mice, and to explore the role of Wnt/b-catenin signaling pathway in behavioral regulation of depression mice. MATERIALS AND METHODS: The mouse model of depression was established via chronic unpredictable mild stress (CUMS). All mice were randomly divided into control group (n=12), model group (n=12), and fluoxetine group (n=12). The expression level of miR-155 in the hippocampus of mice in each group was detected via quantitative Polymerase Chain Reaction (qPCR). The changes in the behaviors of mice in each group were evaluated via behavioral experiments. The apoptosis level in the hippocampus of mice in each group was detected via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Moreover, the content of inflammatory factors in the hippocampus of mice in each group was detected using the enzyme-linked immunosorbent assay (ELISA) kits. The expression levels of Wnt/b-catenin signaling pathway-related proteins in each group were detected via Western blotting. RESULTS: The expression level of miR-155 in the hippocampus was significantly higher in model group than that in control group (p<0.01). Meanwhile, the expression level of miR-155 was significantly lower in fluoxetine group than that in model group (p<0.01). There were no statistically significant differences in the crossing score and rearing score in the open field test among groups (p>0.05). Compared with those in control group, the immobility time in tail suspension test and forced swimming test were significantly increased (p<0.01), while the sucrose preference degree significantly declined (p<0.01) in model group. Fluoxetine could significantly reduce the immobility time in tail suspension test and forced swimming test (p<0.01) and increase the sucrose preference degree (p<0.01) in model group. The number of TUNEL-positive cells in the hippocampus of mice in model group was significantly larger than that in control group (p<0.01). Fluoxetine could effectively reduce the number of TUNEL-positive cells in the hippocampus (p<0.01). Compared with those in control group, the content of tumor necrosis factor-α (TNF-a), interleukin-1b (IL-1b), and IL-6 in the hippocampus was significantly increased (p<0.01), while the content of IL-10 was significantly decreased (p<0.01) in model group. Fluoxetine could effectively reduce the content of TNF-a, IL-1b, and IL-6 (p<0.01) and increase the content of IL-10 (p<0.01). Besides, in model group, the expression levels of dishevelled-1 (DVL-1) and b-catenin in hippocampus remarkably declined (p<0.01), while the expression levels of glycogen synthase kinase-3b (GSK-3b) and adenomatous polyposis coli (APC) were remarkably increased (p<0.01) compared with those in control group. Fluoxetine could effectively lower the expressions of GSK-3b and APC in the hippocampus (p<0.01) and increase the expressions of DVL-1 and b-catenin (p<0.01) in model group. CONCLUSIONS: MiR-155 is involved in regulating the depression-like behaviors of depression mice through promoting the release of inflammatory factors and the apoptosis of hippocampal neurons. Its mechanism may be related to the inhibition of the Wnt/b-catenin signaling pathway.