By: Anna Nanas, Biological Sciences ‘2024
The relationship between the gut and the brain has garnered increasing attention in recent years. Referred to as the gut-brain axis, this relationship represents bidirectional communication between the central nervous system and the digestive system. To facilitate this communication, the gut-brain axis utilizes various pathways, including the vagus nerve (which manages communication between the brain, heart, and digestive system), and the humoral pathway (through the secretion of peptides or the production of antibodies). Current scientific research from microbiologists and psychiatrists still seeks to explore the extent to which the gut-brain axis is a factor in psychiatric conditions.
Many recent studies have shown that these intricate pathways connecting our brain and gut actually do play an integral role in the manifestation of psychiatric conditions [1]. One argument for the fact that these conditions are impacted by the gut-brain axis is that individuals with conditions such as generalized anxiety disorder and major depressive disorder often present with gastrointestinal issues such as stomach upset or bowel movement changes [2]. Through the release of microbial metabolites and neurotransmitters, the gut microbiome can influence central nervous system function, and conversely, neuropsychological stressors can change the composition of gut flora and epithelial permeability [3]. As a result, generalized anxiety disorder and major depressive disorder are often comorbid with irritable bowel syndrome or inflammatory bowel disease [4].
The development of gastrointestinal symptoms may not be the only aspect of psychiatric diseases in which the gut-brain axis is involved. The composition of the gut microbiome may make a person more susceptible to the development of psychiatric conditions such as depression or anxiety. The signaling pathways of different microorganisms interact with the brain and stress responses differently; some microbiota may have a positive effect on mood whereas others can activate stress responses and negatively impact mood [5]. As the composition of the gut microbiome can be controlled in various ways, such as through fecal microbiome transplant or supplementation with psychobiotics, the notion that gut microbiome composition can impact psychiatric conditions opens up new possibilities for treatment [5].
The aforementioned treatments involve different mechanisms. A fecal microbiome transplant involves transplanting stool from a healthy individual into the affected individual to transfer the microbiota from the healthy stool into the recipient’s microbiome. Psychobiotics refer to prebiotics and probiotics that can impact psychiatric well-being. Prebiotics contain growth factors for microbiota and can be given as a supplement to a patient in order to strengthen their microbiome. Probiotics can also be given as a supplement, but they differ from prebiotics in that they contain live microbiota. An alternative to taking these supplements is adjusting diet to increase consumption of fermented foods, which naturally contain prebiotics and probiotics [6]. Despite its proven effectiveness, the modulation of the microbiome as a treatment for psychiatric conditions is relatively uncommon. Nevertheless, it is undeniably a potential option in treating treatment-resistant psychiatric conditions [7]. Furthermore, incorporating microbiome profiling by tailoring microbiome modulation towards individual needs may allow for the formulation of more effective psychiatric treatments.
Thus, the gut microbiome serves as both a consequence of and a contributing factor to psychiatric conditions, influencing the pathophysiology and pathogenesis of such conditions. As such, microbiota-based interventions hold promise as novel therapeutic modalities for treating psychiatric conditions. Emerging evidence that microbiota-based interventions can impact psychiatric well-being warrants further research into both the molecular mechanisms underlying the neuroendocrine interactions between the gut and the brain and microbiota-based interventions for treating psychiatric conditions.
References
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North, C. S., Alpers, D. H., Thompson, S. J., & Spitznagel, E. L. (1996). Gastrointestinal symptoms and psychiatric disorders in the general population. Digestive Diseases and Sciences, 41(4), 633–640. https://doi.org/10.1007/bf02213117
Li, X.-J., You, X.-Y., Wang, C.-Y., Li, X.-L., Sheng, Y.-Y., Zhuang, P.-W., & Zhang, Y.-J. (2020, August). Bidirectional brain-gut-microbiota axis in increased intestinal permeability induced by central nervous system injury. CNS neuroscience & therapeutics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7366750/
Mayer, E. A., Ryu, H. J., & Bhatt, R. R. (2023). The neurobiology of Irritable bowel syndrome. Molecular Psychiatry, 28(4), 1451–1465. https://doi.org/10.1038/s41380-023-01972-w
Aizawa, E., Tsuji, H., Asahara, T., Takahashi, T., Teraishi, T., Yoshida, S., Ota, M., Koga, N., Hattori, K., & Kunugi, H. (2016). Possible association of bifidobacterium and lactobacillus in the gut microbiota of patients with major depressive disorder. Journal of Affective Disorders, 202, 254–257. https://doi.org/10.1016/j.jad.2016.05.038
Dahiya, D., & Nigam, P. S. (2022). Probiotics, prebiotics, synbiotics, and fermented foods as potential biotics in nutrition improving health via microbiome-gut-brain axis. Fermentation, 8(7), 303. https://doi.org/10.3390/fermentation8070303
Evrensel, A., & Ceylan, M. E. (2018). Fecal microbiota transplantation in the treatment-resistant psychiatric disorders. Treatment Resistance in Psychiatry, 369–376. https://doi.org/10.1007/978-981-10-4358-1_24
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