Microbial communities in the body could influence brain and mental health states through signaling pathway. The production of the neurotransmitter serotonin in the cells in the gut which may affect the signaling in the brain via the systemic interaction between the gut and the brain. In the study of a biologics, Hsiao, the research examined how certain metabolites from gut microbes are related to body’s serotonin ( 5-hydroxytryptamine, 5-HT) production. The microbiota plays a significant role in regulating host 5-HT. The indigenous spore- forming bacteria from the mouse and human microbiota leads 5-HT biosynthesis which affects host physiology. The gut microbiota modulates the peripheral serotonin level of the host [1]. Besides, the intestinal microbiome can prompt immune cells to produce cytokine which influences the brain via signaling of other cell types. Another example is the production of butyrate of the microbes which is correlated with the activity of cells in the blood-brain permeability. The gut microbes break down the carbohydrates into short-chain fatty acids such as fatty acid butyrates which enhance the blood-brain barrier by tightening connections between cells [2].
Besides, the brain and mental states may also influence on the gut microbiota through changes in behaviors or release of neurotransmitter, hormones, and steroid. For example, the release of catecholamines and norepinephrine during stress into the GI may cause the dysregulation of the gut-brain axis via the changes in GI motility, the mucus secretion, and epithelial cells. These might lead to different gut diseases. Also, in the early maturity life in the animal, the stress increased the level of corticosterone production and inflammatory cytokines. The stress situation may cause the decrease of gut function related to changes in the microbial community and gut diversities. Moreover, the development of postinfectious irritable bowel syndrome is correlated to stress-related psychosocial factions which could be somatization, hypochondriasis, and neuroticism [3].
Overall, microbes and mental health states are linked together. From the people with ASD have IBD and other gastrointestinal problems. There are different abundances of microbial communities in ASD patients in the relationship with gastrointestinal diseases. In the case study of John Rodakis, his son showed improvement in the gut and behavioral autism after using antibiotic treatments. This suggested that the researchers would need to conduct more studies about different members of gut microbiota which are associated with autism and neurological states [4]. From the lecture this week, there are proposals about influences of microbes such as bipolar disorder, obsessive-compulsive disorder, post-traumatic stress disorder, schizophrenia. However, there are also many skepticisms about these proposals which make this topic become controversial. I think that whether microbial communities in the body could influence brain and mental health states or brain and mental health states could influence microbial communities in the body should depend on specific patient cases.
Yano, J. M., Yu, K., Donaldson, G. P., Shastri, G. G., Ann, P., Ma, L., … & Hsiao, E. Y. 2015. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell, 161(2), 264-276.
Smith, P. 2015. The tantalizing links between gut microbes and the brain. Nature.526: 312-314
Thakur AK, Shakya A, Husain GM, Emerald M, Kumar V. 2014. Gut-Microbiota and Mental Health: Current and Future Perspectives. J Pharmacol Clin Toxicol 2(1):1016.
Rodakis, J. 2015. An n= 1 case report of a child with autism improving on antibiotics and a father’s quest to understand what it may mean. Microbial ecology in health and disease, 26.
