Brain Neurotransmitter Modulation by Gut Microbiota in Anxiety and Depression

Abstract

Anxiety and depression are highly prevalent mental illnesses worldwide and have long been thought to be closely associated to neurotransmitter modulation. There is growing evidence indicating that changes in the composition of the gut microbiota are related to mental health including anxiety and depression. In this review, we focus on combining the intestinal microbiota with serotonergic, dopaminergic, and noradrenergic neurotransmission in brain, with special emphasis on the anxiety- and depression-like behaviors in stress-related rodent models. Therefore, we reviewed studies conducted on germ-free rodents, or in animals subjected to microbiota absence using antibiotics, as well as via the usage of probiotics. All the results strongly support that the brain neurotransmitter modulation by gut microbiota is indispensable to the physiopathology of anxiety and depression. However, a lot of work is needed to determine how gut microbiota mediated neurotransmission in human brain has any physiological significance and, if any, how it can be used in therapy. Overall, the gut microbiota provides a novel way to alter neurotransmitter modulation in the brain and treat gut–brain axis diseases, such as anxiety and depression.

Exploring the Role and Potential of Probiotics in the Field of Mental Health: Major Depressive Disorder

“…Depletion in either of these neurotransmitters contributes to the development of various neuropsychiatric disorders including depression. Most antidepressants work by restoring the levels of monoamine neurotransmitters (i.e., 5-HT, DA and NE) [115][116][117][118]. The gut microbiota is involved in the modulation of neurotransmitters via either neural, humoral or immune-mediated pathways.…”

“…The gut microbiota is involved in the modulation of neurotransmitters via either neural, humoral or immune-mediated pathways. Dysregulation and alteration in the gut microbiota have been found to impair the neurotransmitter circuitry [117,119]. The vagus nerve is one of the crucial mediators between the gut and the brain via the neural pathway, which is involved in the regulation of neurotransmitters by the gut microbiota [97,115].…”

Dietary Fat Effect on the Gut Microbiome, and Its Role in the Modulation of Gastrointestinal Disorders in Children with Autism Spectrum Disorder

“…Members of the genera Lactobacillus and Bifidobacterium synthesize gamma-aminobutyric acid (GABA); Lactobacillus synthesizes acetylcholine; Bacillus and Serratia synthesize dopamine; Candida, Streptococcus, Escherichia, and Enterococcus synthesize serotonin; and Escherichia, Bacillus and Saccharomyces synthesize norepinephrine [58]. Alterations in these molecules mediate the effect of GM on brain development [59,60]. Animal studies have proven that the modulation of the GM can affect the manifestations of oxytocin, vasopressin, and brain-derived neurotrophic factor (BDNF), and improve the function of microglial cells, thus it can enhance behavior, learning, and memory in humans [59,61].…”

The Gut-Microbiota-Brain Axis in Autism Spectrum Disorder

“…Gut microbial metabolites include short-chain fatty acids, as well as vitamins essential for human health (24,45,46). Other microbial products include compounds that act as neurotransmitters that may influence synapse function and communication with the brain (47,48). For example, gastrointestinal disorders and changes in the gut microbiota are known to affect serotonin signaling in the gut and the brain (49,50).…”