Microbiota-gut-brain Axis and its Role in Depression: A Narrative Review

The mutual peaceful coexistence of microbiota with their host ensures normal gut motility and secretory functions, mucosal immune function and absorption of nutrients. Emerging evidences suggest the role of gut microbiota in a bidirectional communication between Central Nervous System (CNS) and gastrointestinal system, referred to as gut-brain axis. The findings largely drawn from preclinical studies show that gut microbiome can modulate brain and behaviour via vagal nerve, inducing tryptophan metabolism pathways, affecting synthesis of neurotransmitters, production of bacterial metabolites, such as Short-Chain Fatty Acids (SCFAs), by Hypothalamus-Pituitary-Adrenal Axis (HPA) alterations and through neuroimmune pathways. Psychological stress could lead to abnormal changes in composition of gut microbiome and disruption of intestinal barrier functions and it also has an underlying role in neurobiology of depression which has multifactorial aetiology. The perturbations of gut microbiota have been associated with depression and might have a contributory role in development of depressive symptomatology. The current understanding of microbiota gut-brain axis is still in early stages and drawn from preclinical and clinical data and therefore it warrants further research to elucidate its role in stress and depression and future development of novel therapies targeting microbiota-gut-brain axis for stress related disorders such as depression