Gut microbiota should be considered as a whole instead of focusing on some species to study the cause of AD; (iii) the rats receiving the microbiota transplantation from AD patients showed some behavioral alterations associated with alcohol dependence, including increased anxiety- and depression-like behaviors, reduced exploratory and recognition memory, and higher alcohol preference; and (iv) the gut microbiota dysbiosis induced by alcohol may involve the development of alcohol addiction through regulating the endogenous CCK and related receptors. Here, CCK is linked to major depressive disorder.