PROMPT: Describe how microbial communities in the body could influence brain and mental health states. Then, describe how brain and mental health states could influence microbial communities in the body. In what ways might these promote health and/or disease?
One thing that has become increasingly studied and researched is the relation with the gut microbiome and mental health. Coincidentally, that is the exact topic of my final essay paper. Even though this is a topic which has interested me for a little while now, and I have done some independent reading on the subject, the process of gathering info for my paper has brought many new theories to my attention. Results from studies I have read have provided information about new ways of how the gut microbiota affects the brain and mental health.
The connection between the gut microbiome and the brain is referred to as the ‘Microbiome-gut-brain-axis’ and involves the bidirectional relation between the Central Nervous System, the Enteric Nervous System, and the gastrointestinal tract. (1) The Central Nervous System encompasses the brain and spinal cord and is well known. The Enteric Nervous system involves approximately 500 million nerve cells which can control all the normal functions of digestion even if separated from the brain. (2) These two nervous systems connect via the Vagus nerve, and thus a direct line is made connecting the brain and gut.
With respect to the gut affecting the brain/mental health, one of the most fascinating facts relates to the percentage of all endogenous neurotransmitters and neuroactive chemicals that are made in the gut. 5-hydroxytryptamine (5-HT), more commonly referred to as ‘serotonin; plays a large role in our mental health. Imbalances and low concentrations of serotonin are believed to cause a wide array of mental disorders, and thus serotonergic drugs are often the most widely used treatment. When one thinks about neurotransmitters, and chemical imbalances of the brain, its easy to assume that all or a significant majority of neurotransmitters are both made and stored solely in the brain. New studies show that this couldn’t be further from the truth. Approximately 90% of ALL endogenous serotonin is synthesized in the gut! (3) A study using mice found that the presents of some microbes regulate the hosts serotonin levels, and having these microbes led to significantly higher serotonin levels than in mice birthed and raised germ free. (3) Since the microbes are able to alter the levels of endogenous serotonin, and serotonin plays a large role in mental health, the microbes have a direct influence on the mental health of their host!
As mentioned when describing the Microbiome-gut-brain-axis as a ‘bidirectional’ relation, the connection and influences go both ways. Mental health can have an impact on the make up of gut microbiomes in a few ways. Chronic stress and Anxiety due to various mental disorders can lead to an increase in stomach acid production. This changes the acidity of the stomach and intestines and impacts which microbes can successfully colonize the area. Depression can lead to a lack of personal hygiene, and poor dietary habits, which both can have an impact on an individual’s microbiota. Bulimia Nervosa, an eating disorder characterized by binge eating followed by forced self-induced emesis to prevent the absorption of the caloric contents of the food, can introduce microbes to new areas of the digestive tract as they are physically relocated during episodes of vomiting.
The microbiome of our gut, the enteric nervous system, and the central nervous system are connected in ways never thought of or studied before. Its amazing learning how two incredibly different specialized regions of the body can have such a collaborative impact on each other. As technology advances and new studies are done, its almost certain that new connections between the organs never thought of before will be discovered, and new ways of indirectly treating diseases and illness affecting different organs will be designed and target the connected organs.
- Mayer E, Tillisch K, Gupta A. 2015. Gut/brain axis and the microbiota. Journal of Clinical Investigation 125:926-938.
- https://www.youtube.com/watch?v=_PLD5RLLvfQ
- Yano J, Yu K, Donaldson G, Shastri G, Ann P, Ma L, Nagler C, Ismagilov R, Mazmanian S, Hsiao E. 2015. Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis. Cell 161:264-276.
