GCG and major depressive disorder: In a chronic unpredictable mild stress (CUMS) depression mouse model, Clostridium butyricum was found to attenuate depressive-like behavior by increasing 5-HT, Glucagon-like peptide-1 (GLP-1), and Glucagon-like peptide 1 receptor (GLP-1R) concentrations and upregulating BDNF expression [87].