Association between intestinal microbiota and major depressive disorder:: a literature review

OBJECTIVE: To present a literature review on the relationship between intestinal microbiota (IM) and Major Depressive Disorder (MDD). METHODS: We consulted the PubMed database, using the following MeSH terms, that associate depression with IM and probiotics: “gut microbiota and major depressive disorder", "microbiome and major depressive disorder", "microbiome and mental diseases", "microbiome and mental disorders", "microbiome and mood disorders", "probiotics and mood". In addition to these, the MeSH terms "probiotics" or "Bifidobacterium" or "Lactobacillus", associated with "depression" or "major depressive disorder" were included. RESULTS: It was demonstrated that dysbiosis induced a depression like behavior in animals. These animals also presented molecular characteristics observed in other models of induction of depression in animals, such as reduction of Brain-Derived Neurotrophic Factor (BDNF) levels, increase of inflammatory mediators, exaggerated response to Hypothalamic-Hypophysis-Adrenal axis (HHA) and modifications serotonin and tryptophan metabolism. In humans, changes in the amount and microbial diversity of the intestine have been shown to be linked to depression. Furthermore, the administration of probiotic bacteria reduced depressive symptoms. CONCLUSION: In fact, studies indicate that dysbiosis is closely related to the development of depressive symptoms. However, a deeper assessment of the microbiota-gut-brain axis becomes necessary to unravel all microbiota-depression connections.