Literature Review: The Microbiota-Gut-Brain Axis in Mental Health and Neurodegeneration: Mechanisms, Evidence, and Therapeutic Implications

Tanvi Agrawal

Abstract: The microbiota-gut-brain axis represents a bidirectional communication system linking the gastrointestinal tract and central nervous system through neural, endocrine, immune, and metabolic pathways. This review examines its role in neuropsychiatric and neurodegenerative disorders, including depression, anxiety, Parkinson?s disease, and Alzheimer's disease. A structured synthesis of peer-reviewed literature from 2015 to 2025 was conducted to evaluate key communication mechanisms and associated clinical evidence. Findings indicate that immune signaling and neuroinflammation provide the most consistent mechanistic link between gut dysbiosis and brain dysfunction, while microbial metabolites and vagal pathways are strongly supported in preclinical models. However, human evidence remains largely associative, with limited causal validation. Emerging interventions, including psychobiotics and microbiota transfer therapies, demonstrate preliminary clinical benefits but are constrained by small sample sizes and methodological variability. Overall, the field requires standardized longitudinal and interventional studies to establish causality and enable clinically actionable applications.

Keywords: Microbiota-Gut-Brain-Axis (MGBA), gut microbiome, neuroinflammation, neuroimmune signalling, dysbiosis, psychobiotics, HPA axis, neurodegenerative disorders, vagus nerve, short-chain fatty acids (SCFAs), fecal microbiota transplantation

How to Cite?: Tanvi Agrawal, "Literature Review: The Microbiota-Gut-Brain Axis in Mental Health and Neurodegeneration: Mechanisms, Evidence, and Therapeutic Implications", Volume 15 Issue 3, March 2026, International Journal of Science and Research (IJSR), Pages: 1777-1786, https://www.ijsr.net/getabstract.php?paperid=SR26328065106, DOI: https://dx.dx.doi.org/10.21275/SR26328065106

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