The correlation between gut microbiota and both neurotransmitters and mental disorders: A narrative review

Abstract

The gastrointestinal tract is embedded with microorganisms of numerous genera, referred to as gut microbiota. Gut microbiota has multiple effects on many body organs, including the brain. There is a bidirectional connection between the gut and brain called the gut-brain-axis, and these connections are formed through immunological, neuronal, and neuroendocrine pathways. In addition, gut microbiota modulates the synthesis and functioning of neurotransmitters. Therefore, the disruption of the gut microbiota in the composition or function, which is known as dysbiosis, is associated with the pathogenesis of many mental disorders, such as schizophrenia, depression, and other psychiatric disorders. This review aims to summarize the modulation role of the gut microbiota in 4 prominent neurotransmitters (tryptophan and serotonergic system, dopamine, gamma-aminobutyric acid, and glutamate), as well as its association with 4 psychiatric disorders (schizophrenia, depression, anxiety disorders, and autism spectrum disorder). More future research is required to develop efficient gut-microbiota-based therapies for these illnesses.

Figure 1.

The role of gut microbiota in both neurotransmitters (including serotonin, dopamine, GABA, and glutamate), and psychiatric illnesses (including depression, anxiety, schizophrenia, and ASD) through the gut-brain axis, which comprises several pathways and mediators such as immunoregulation, the vagus nerve, the HPA axis, bacterial metabolites. Hence, therapeutic applications targeting the gut microbiota (such as FMT, diet, probiotics, and prebiotics) may give rise to more promising and efficient treatments for these disorders in the future. ASD = autism spectrum disorder, FMT = fecal microbiota transplantation, HPA axis = hypothalamic-pituitary-adrenal axis.