GCG and major depressive disorder: Clostridioides butyricum demonstrated significant effects by increasing 5-HT and glucagon-like peptide-1 (GLP-1), upregulating BDNF expression, and promoting GLP-1 secretion and GLP-1 receptor expression (Sun et al., 2018) and GLP-1 has been reported to possess the potential to alleviate depression by regulating neuroinflammation, neurotransmitters, neurogenesis, and synaptic function (Kim et al., 2020).