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Cognitive Science: An Introduction/Gut brain

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The Gut Brain

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The connection between the gastrointestinal system and the human brain is being increasingly researched to discover the extent how the organ systems influence each another. Scientific exploration of this connection is significantly changing medicine’s understanding of the link between digestion, mood, health, and thought processes. The signalling that occurs between the gastrointestinal tract and the brain is considered vital for maintaining the body’s homeostasis, regulating behaviour, and reducing the occurrence of illness [1] The link of communication between the gut and the brain are critical for maintaining healthy brain function and regulating general health.

The Gut-Brain Axis

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The biochemical signalling between the gastrointestinal tract and the central nervous system is referred to as the gut-brain axis. Several components of the body make up to the gut-brain axis including the central nervous system, neuroendocrine, neuroimmune system, the hypothalamic-pituitary-adrenal axis, the sympathetic and parasympathetic components of the autonomic nervous system, the enteric nervous system, the vagus nerve, and the gut microbiota.[2]

A significant demonstration of the interaction between the gut and brain was conducted by Ivan Pavlov. Pavlov’s salivating dog experiment showed the cephalic phase of digestion which subsequently released gastric and pancreatic secretions in response to sensory signals, particularly the smell and sight of food.[3]

The gut-brain axis is considered a complex bidirectional communication system, mediated by hormonal, immunological, and neural signals [4] Within the digestive tract lives microorganisms defined as gut microbiota, a complex community which contains the largest quantity of bacteria that provides a barrier to pathogenic organisms.[5]

A symbiotic relationship is sustained between the gut microbiota and humans. These microorganisms benefit humans by collecting energy, absorbing short-chain fatty acids (acetate, butyrate, and propionate), synthesizing vitamin B and K, and metabolizing bile acids, sterols, and xenobiotics.[6] Dysregulation of the gut microbiota has been correlated with various inflammatory and autoimmune conditions. Further, alterations in diet and overall health have been linked to changes in the composition of gut microbiota.[7]

The composition of an individual’s gut microbiota depends on several factors including the mode of delivery at birth, genetic predisposition, age, nutrition, physical activity, environmental factors, stress, infections, other diseases, and the use of antibiotics.[8] As well, psychological make-up and brain function are now considered to have a reciprocal relationship with the gut. The gut-brain axis provides the gut microbiota with a route that subsequently impacts neurodevelopmental processes and brain functions. Metabolic diseases, psychiatric and comorbid non-psychiatric disorders are associated with a dysregulation of the gut-brain axis communication.[9] Alterations of the gut microbiota threaten its composition and function. This contributes in turn to the disruption of existing molecular dialogue between the gut and brain, potentially resulting in various ailments.

The Gut-Brain and Health

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Numerous studies have sought to determine the precise correlation between gut and brain activity, and this affects human health. The interaction between the gastrointestinal system and the brain has been linked to several disorders including, anxiety, depression, Parkinson’s disease, and more.[10] Some preventative measures for these disorders have proven to be effective. Regulating the gut microbiota can restore health and decreases risk of future illness.

An increasing body of research has demonstrated the relationship between the gut microbiota and the influence it has on an individual’s health. Those with neurodevelopmental disorders, such as attention-deficit hypersensitivity disorders (ADHD) and autism spectrum disorders (ASD), typically have gastrointestinal issues and altered gut microbiota.[11] Due to ADHD and ASD being linked to gastrointestinal problems, targeting the gut-brain connection as a treatment method has been proposed as a promising possibility. Further, it has been suggested that gut microbiota may contribute to the development of autoimmune diseases like multiple sclerosis (MS).[12] Stress-induced gut alterations can impact the brain and behaviour, and diseases like MS are triggered or worsened by stress.[13] Moreover, obesity has been referred to as a psychiatric disease that is commonly associated with depression and other neuropsychiatric disorders that can be caused by the gut microbiota’s influence on energy balance and weight. Additionally, a risk factor for neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease is type 2 diabetes, which can be treated using targeted drugs that positively impact the gut-brain axis.[14]

Mood disorders, such as anxiety and depression, have been linked to both brain and gastrointestinal abnormalities.[15] Further, the hyperactivity or dysregulation of the hypothalamic-pituitary-adrenal axis is one of the most reliable biological indicators of major depression and anxiety. A correlation has been discovered between the hypothalamic-pituitary-adrenal reactivity and gut microbiota demonstrating the role of gut microbiota in managing stress and mitigating stressor-responses.[16] For psychiatric disorders such as anxiety and depression, the use of psychobiotics, probiotics, and prebiotics facilitate changes in emotion, cognition, behaviour, and neural networks. Probiotics can further decrease feelings of stress and help mitigate symptoms of depression and anxiety.[17] Further, a growing number of studies have demonstrated that probiotics regulate the immune system against infectious disorders, cancers, immuno-inflammatory diseases, and they increase the defence against the common cold and influenza.[18] Significant empirical evidence now supports that cognitive and emotional processes via the gut-brain axis can be altered through the use of prebiotics and probiotics.

References

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  1. ↑ Cryan, J. F. & O’Mahony, S. M. (2011). The microbiome-gut-brain axis: From bowel to behavior. Neurogastroenterology & Motility, 23, p. 187-192. doi: 10.1111/j.1365-2982.2010.01664.x
  2. ↑ Wang, Y. & Kasper L. H. (2014). The role of microbiome in central nervous system disorders. Brain Behavior & Immunity, 38, p. 1-12. doi: 10.1016/j.bbi.2013.12.015
  3. ↑ Filaretova, L. & Bagaeva, T. (2016). The realization of the brain-gut interactions with corticotropin-releasing factor and glucocorticoids. Current Neuropharmacology, 14(8), p. 876-881. doi: 10.2174/1570159X14666160614094234
  4. ↑ Agusti, A., Garcia-Pardo, M. P., Lopez-Almela, I., Campillo, I., Maes, M., Romani-Perez, M. & Sanz, Y. (2018). Interplay between the gut-brain axis, obesity and cognitive function. Frontiers in Neuroscience, 12(155), p. 1-17. doi: 10.3389/fnins.2018.00155
  5. ↑ Saxena, R. & Sharma V. K. (2016). A metagenomic insight into the human microbiome: Its implications in health and disease. Medical and Health Genomics, p. 107-119. doi: 10.1016/B978-0-12-420196-5.00009-5
  6. ↑ Clarke, G., Stilling, R. M., Kennedy, P. J., Stanton, C., Cryan, J. F. & Dinan, T. G. (2014). Minireview: Gut microbiota: The neglected endocrine organ. Molecular Endocrinology, 28(8), p. 1221-1238. doi: 10.1210/me.2014-1108
  7. ↑ Shen, S. & Wong, C. H. Y. (2016). Bugging inflammation: Role of the gut microbiota. Clinical & Translational Immunology, 5(4), p. 1-10. doi: 10.1038/cti.2016.12
  8. ↑ Petra, A. I., Panagiotidou, S., Hatziagelaki, E., Stewart, J. M., Conti, P. & Theoharides, T. C. (2015). Gut-microbiota-brain axis and effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical Therapeutics, 37(5), p. 984-995. doi: 10.1016/j.clinthera.2015.04.002
  9. ↑ Agusti, A., Garcia-Pardo, M. P., Lopez-Almela, I., Campillo, I., Maes, M., Romani-Perez, M. & Sanz, Y. (2018). Interplay between the gut-brain axis, obesity and cognitive function. Frontiers in Neuroscience, 12(155), p. 1-17. doi: 10.3389/fnins.2018.00155
  10. ↑ Petra, A. I., Panagiotidou, S., Hatziagelaki, E., Stewart, J. M., Conti, P. & Theoharides, T. C. (2015). Gut-microbiota-brain axis and effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical Therapeutics, 37(5), p. 984-995. doi: 10.1016/j.clinthera.2015.04.002
  11. ↑ Petra, A. I., Panagiotidou, S., Hatziagelaki, E., Stewart, J. M., Conti, P. & Theoharides, T. C. (2015). Gut-microbiota-brain axis and effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical Therapeutics, 37(5), p. 984-995. doi: 10.1016/j.clinthera.2015.04.002
  12. ↑ Dinan, T. G., & Cryan, J. F. (2012). Regulation of the stress response by the gut microbiota: Implications for psychoneuroendocrinology. Psychoneuroendocrinology, 37(9), 1369–1378. https://doi.org/https://doi.org/10.1016/j.psyneuen.2012.03.007
  13. ↑ Petra, A. I., Panagiotidou, S., Hatziagelaki, E., Stewart, J. M., Conti, P. & Theoharides, T. C. (2015). Gut-microbiota-brain axis and effect on neuropsychiatric disorders with suspected immune dysregulation. Clinical Therapeutics, 37(5), p. 984-995. doi: 10.1016/j.clinthera.2015.04.002
  14. ↑ Kim, D. S., Choi, H., Wang, Y., Luo, Y., Hoffer, B. J. & Greig, N. H. (2017). A new treatment strategy for Parkinson’s disease through the gut-brain axis: The glucagon-like peptide-I receptor pathway. Cell Transplantation, 26(9), p. 1560-1571. doi: 10.1177/0963689717721234
  15. ↑ Dinan, T. G., & Cryan, J. F. (2012). Regulation of the stress response by the gut microbiota: Implications for psychoneuroendocrinology. Psychoneuroendocrinology, 37(9), 1369–1378. https://doi.org/https://doi.org/10.1016/j.psyneuen.2012.03.007
  16. ↑ Tran, N., Zhebrak, M., Yacoub, C., Pelletier, J. & Hawley, D. (2019). The gut-brain relationship: Investigating the effect of multispecies probiotics on anxiety in a randomized placebo-controlled trial of healthy young adults. Journal of Affective Disorders, 252, p. 271-277. doi: 10.1016/j.jad.2019.04.043
  17. ↑ Pusceddu, M. M., Murray, K., & Gareau, M. G. (2018). Targeting the Microbiota, From Irritable Bowel Syndrome to Mood Disorders: Focus on Probiotics and Prebiotics. Current Pathobiology Reports, 6(1), 1–13. https://doi.org/10.1007/s40139-018-0160-3
  18. ↑ Cerdó T, Ruíz A, Suárez A, Campoy C. Probiotic, Prebiotic, and Brain Development. Nutrients. 2017; 9(11):1247
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