In addition, the microbiota dominated by bifidobacterium mediates communication with the CNS using neurotransmitters such as gamma-aminobutyric acid (GABA), 5-hydroxytryptamine (5-HT), neuropeptides, corticotropin-releasing hormone secreted by the HPA axis, and short-chain fatty acids (such as ethylene hydrochloric acid) (52), For example, Bifidobacterium infantilum can affect central serotonin transmission by increasing plasma tryptophan (61), mediating MGBA bidirectional exchange to regulate metabolic and immune responses in patients since improving depression. This evidence concerns the gene CRH and major depressive disorder.