Background Although the link between gut microbiota and depression has been suggested,changes of gut microbiota vary largely among individuals with depression.Aims Explore the heterogeneity of microbiota-gut-brain axis and new pathogenic characteristics in murine models of depression.Methods Adolescent female mice were randomly divided into control(CON)group(n=10),chronic unexpected mild stress(CUMS)group(n=15)and dexamethasone(DEX)group(n=15).Mice in the DEX group were gavaged twice a day with 0.2 mg/kg of DEX for 5 weeks,whereas CON mice were given the same amount of solvent.Mice in the CUMS group were exposed to stressors.After behavioural evaluations,all mice were sacrificed for harvesting tissues and blood samples.Enzyme-linked immunosorbent assay(ELISA)was conducted for measuring levels of corticosterone(CORT)and interleukin-1 β(IL-1β)in sera,whereas levels of protein expression in colon and hippocampal tissues were examined by western blot.Faecal microbial communities were analysed by sequencing 16S rDNAs.Results Mice in CUMS and DEX groups exhibited severe depression-like behaviours.Compared with CON mice,CUMS-exposed mice showed a significant increase in both α and β diversity.Prevotellaceae and Desulfovibrio were enriched,whereas Bacilli were decreased in the faeces of mice in the CUMS group.DEX-treated mice had a decrease in the abundance of Clostridium ⅩⅧ.Levels of occludin in colon tissue of DEX-treated mice were reduced.Relative to mice in the CON and CUMS groups,DEX-treated mice contained higher serum levels of CORT and IL-1 β.Compared with CON mice,mice in the DEX and CUMS groups had higher levels of IL-1 β in sera and lower levels of glial fibrillary acidic protein(GFAP),Nestin,Synapsin-1 and P2Y12 receptor in the hippocampus.Conclusions Changes of gut microbiota diversity,intestinal integrity and neuroinflammation in the brain contribute to CUMS-induced depression,whereas pathobionts and excessive immunosuppression with damaged neuronal synapses is a basis of the DEX-induced depression.