The brain’s ability to control and regulate the gut using nerves and various signals is well established. However, scientists have recently discovered that this is not the only way in which those two systems in our bodies communicate. It turns out that not only is this communication quite complex; but also bidirectional. Your gut influences your nervous system right back!
A Steady Introduction
The gut-brain axis is the key to this fascinating connection, and this axis is the connection between the microbiota and the nervous system. The microbiota consists primarily of bacteria, viruses and fungi, with up to 1014 microorganisms living in your gut! Those organisms have a profound impact on the immune system, digestion, nutrients absorption and more. If the balance in the microbiota is disrupted, this can lead to various health problems.
There are many ways the microbiota can “communicate” with the brain. The neurologic pathway is one of the most famous forms of communication, where the microbiota can produce and secrete different neurotransmitters responsible for, e.g. emotion and memory, regulating brain activity via the vagus nerve- the main nerves comprising the nervous system. The gut is also regulated by the limbic system in the brain which is especially active when we are stressed. Scientists think this is a reason behind why some people experience GI problems when anxious.
Another famous mode of communication is the metabolic pathway; through this, so-called bacterial metabolites influence the activity of the sympathetic nervous system. Bacterial metabolites are bacteria that are either necessary for the metabolism, or produced during the process. These metabolites can cross the blood-brain barrier to regulate the homeostasis within the brain. The term ‘homeostasis’ is a biological umbrella term used to describe any process used by a living thing to maintain the stable conditions necessary for its survival. Disruptions to the aforementioned processes has been linked to the development of autism in children.
The endocrine pathway involves the gut directly impacting synthesis of substances in control of the sleep cycle, feeding, blood pressure and a myriad of other functions through changing the availability of and access to nutrients to absorb and use in the body’s many energy dependent processes. This has a direct impact on cognitive function.
The Gut-Brain Axis and Psychiatric Diseases
Thanks to animal models, scientists have been able to investigate the impact of microbiota changes on different psychiatric disorders, particularly Major Depressive Disorder (MDD). Interestingly, it was found that both mice and patients with MDD have a reduced number of Faecalibacterium, and increased numbers of Enterobacteriaceae and Alistipes, which are three colonies of bacteria naturally present in our gut. However, dysbiosis (abnormalities in microbiota), especially in these colonies, can lead to inflammation, which has been previously linked to depression.
This evidence is still not conclusive, but scientists have made important strides in research regarding , restoring the balance in the gut and alleviated depressive symptoms. Scientists have tested this hypothesis by treating patients with MDD with pre- and probiotics. The evidence shows that this type of treatment might be effective; however, we have to be cautious about drawing conclusions from this research because the improvement was usually short-term and the samples were very small. Still, investigation of the gut-brain axis in relation to depression might shed light on possible treatments which are very much needed.
Appleton, J. (2018). The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integrative Medicine: A Clinician’s Journal, 17(4), 28–32. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6469458/
Getty Images. (2022). The gut-brain axis. Futurecdn.net. https://cdn.mos.cms.futurecdn.net/YXzSDgg6TmdxhyTNTJjJkc-320-80.jpg
Noonan, S., Zaveri, M., Macaninch, E., & Martyn, K. (2020). Food & mood: a review of supplementary prebiotic and probiotic interventions in the treatment of anxiety and depression in adults. BMJ Nutrition, Prevention & Health, 3(2), bmjnph-2019-000053. https://doi.org/10.1136/bmjnph-2019-000053
Rege, S. (2019, April 22). The Simplified Guide to the Gut Brain Axis – How the Gut Talks to the Brain. Psych Scene Hub. https://psychscenehub.com/psychinsights/the-simplified-guide-to-the-gut-brain-axis/
Rutsch, A., Kantsjö, J. B., & Ronchi, F. (2020). The Gut-Brain Axis: How Microbiota and Host Inflammasome Influence Brain Physiology and Pathology. Frontiers in Immunology, 11. https://doi.org/10.3389/fimmu.2020.604179