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?
The human gastrointestinal tract harbors trillions of microorganisms, consisting of up to 1,000 or so different bacterial species. These bacteria, known collectively as the gut microbiota, perform a number of vital functions in our body. They defend against pathogens, aid in digestion and nutrient absorption, produce vitamins (K and B), and boost our immune system. Some of the products of metabolism by these bacteria have been found to be neurotransmitters and interact with the enteric nervous system. These neurotransmitters can start at the peripheral nervous system and then be transferred to the the central nervous system were they can effect brain chemistry. Research shows that people suffering from gastrointestinal disorders are more susceptible to anxiety related disorders. Although the underlying mechanism is not fully understood as yet, there is clear evidence of a connection between the microbiota, gut and brain.
These mechanisms can be related in reverse were the brain can effect the environment in the gut. This happens through stress related incidences. Early life stress has been implicated in many psychiatric disorders ranging from depression to anxiety. A research study “Maternal separation as a model of brain-gut axis dysfunction.” describes the components of the brain-gut axis individually and how they are altered by maternal separation. The separated phenotype is characterised by alterations of the intestinal barrier function, altered balance in enteric microflora, exaggerated stress response and visceral hypersensitivity, which are all evident in IBS (1). This is also the case in psychological, sexual and physical abuse which can lead to high amounts of stress or the release of the release of cortisol, which influences many bodily functions such as metabolic, psychological and immunological functions. So this may be because the establishment of stable gut microbiota is disrupted by altered metabolic functions.
This image depicts the Brain-Gut axis and how stress could interrupt the homeostasis between the two. Probiotics, antibiotics and fecal transplants are all ways to combat the dysbiosis that can take place from stress.
http://www.jpp.krakow.pl/journal/archive/08_15/articles/02_article.html
O’Mahony, S. M., Hyland, N. P., Dinan, T. G., & Cryan, J. F. (2011). Maternal separation as a model of brain–gut axis dysfunction. Psychopharmacology, 214(1), 71-88.
