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A Gut Feeling

Written by Manal Usmani and Edited by Sorina Long

Image by StockSnap on Pixabay.

The microscopic organisms living in our intestines are an essential part of human biology and are commonly known for their assistance in bowel function. Over the past decade, scientific interest has grown, with significant evidence suggesting that gut microorganisms can influence brain function. While most people do not commonly associate the two, it has been established that gut organisms are crucial for appropriate social behavior development​ [1]​.Why and how does the gastrointestinal tract have an effect on our brain? The microbiota communicates with the nervous system through chemical signalling in a typical, healthy physiological system. Specifically, the composition, species diversity, and transport of these microorganisms are the primary qualities allowing them to influence changes outside of the gastrointestinal system ​[2]​. Microbiota characteristics can increase the susceptibility to psychiatric disorders and evidence for this finding is accumulating and strengthening in the scientific literature space ​[3]​.

Gamma-aminobutyric acid (​GABA) is a major neurotransm​itter responsible for overall regulation of processes in the brain and has notable effects on depression and mood. Neurotransmitters are chemical substances that transfer signals between neurons and their target cells. A past study has established a link between an increased amount of a certain bacteria that is thought to be interacting with GABA signalling and reducing anxiety-like behaviors ​[4]​. Mice with increased amounts of ​Lactobacillus rhamnosus gut bacteria displayed more non-depressive actions than control mice, who had the normal amount of the bacteria ​[4]​. The experimenters concluded that there was decreased GABA signaling in the brains of mice treated with the bacteria. Overall, there was a significant difference between the groups, showing that ​L. rhamnosus ​interacts with the brain and impacts overall mood and psychological health [4]​. Another study has shown that carefully chosen microorganisms can relieve stress and depressive symptoms in mice when they consume prebiotics, foods with special fibers that promote bacterial and fungal growth ​[5]​. The results of these studies imply that gut health is related to mental health and suggest the possible potential of introducing bacterial supplements and treatments in patients with chronic depression and mental illness.

The role of our intestinal microbes in the progression of multiple sclerosis (MS) has also been studied. Multiple sclerosis is a disease in which nerve damage disrupts communication between the brain and the body and can lead to symptoms such as vision loss, fatigue, and difficulty coordinating muscles. Multiple studies have come to the conclusion that the abundances of bacteria in MS patients are different from that in non-MS patients ​[6]​. One study in particular noted that there was an increase in Desulfovibrionaceae ​(​Bilophila​,​ Desulfovibrio ​and Christensenellaceae​) and a decrease in Lachnospiraceae ​and Ruminococcaceae ​in MS patients when compared to that in normal healthy individuals [6]​. This study was designed to look at pediatric cases, which allowed researchers to observe how these compositions start in early MS disease diagnosis. Scientists were also taken aback by the fact that there are multiple neurological disorders, such as autism, that might be a result of the actions of microorganisms in our gut ​[7]​.

The purpose of studying the relationship between the gut and the brain is to decipher disease-causing mechanisms. This is a prerequisite to being able to develop drugs that can redirect atypical neurological physiology to normal functioning. As millions of Americans are impacted by depression, anxiety, and neurological dysfunction, the implications are great; the spectrum of psychological disorders can be tackled by more investigation into this exciting new field of research.

References:

  1. Desbonnet, L., Clarke, G., Shanahan, F., Dinan, T.G., Cryan, J.F. (2013). Microbiota is essential for social development in the mouse. ​Mol Psychiatry​,19:146–148.
  2. Ho, J.T., Chan, G.C., Li, J.C. (2015). Systemic effects of gut microbiota and its relationship with disease and modulation. ​BMC Immunology​,16:21–34.
  3. Diaz H.R., Wang, S., Anuar, F., Qian, Y., Björkholm, B., Samuelsson, A., Hibberd, M. L., Forssberg, H., Pettersson, S. (2011). Normal gut microbiota modulates brain development and behavior. ​Proceedings of the National Academy of Sciences of the United States of America​, 108:3047–3052.
  4. Bravo, J. A., Forsythe, P., Chew, M. V., Escaravage, E., Savignac, H. M., Dinan, T. G., Bienenstock, J., Cryan, J. F. (2011). Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. ​Proceedings of the National Academy of Sciences of the United States of America​, 108:16050–16055.
  5. Burokas, A., Arboleya, S., Moloney, R.D., Peterson, V.L., Murphy, K., Clarke, G., Stanton, C., Cryan, J.F. (2017). Targeting the Microbiota-Gut-Brain Axis: Prebiotics Have Anxiolytic and Antidepressant-like Effects and Reverse the Impact of Chronic Stress in Mice. ​Biological Psychiatry​, 82:472-487.
  6. Tremlett, H., Fadrosh, D. W., Faruqi, A. A., Zhu, F., Hart, J., Roalstad, S., Graves, J., Lynch, S., Waubant, E. (2016). Gut microbiota in early pediatric multiple sclerosis: a case-control study. ​European journal of neurology​, 23:1308–1321.
  7. Theije, C.G.M., Wopereis, H., Ramadan, M., van Eijndthoven, T., Lambert, J., Knol, J., Garssen, J., Kraneveld, A.D., Oozeer, R. (2014). Altered gut microbiota and activity in a murine model of autism spectrum disorders. ​Brain Behavior Immunity​, 237:197–206.

Published in Medicine

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