The gut, the belly, the gastrointestinal tract, the second brain?!

Contributed by Poyin Chen

Our gastrointestinal (GI) tract has the largest concentration of nerves, second only to the brain. Additionally, the vagus nerve runs through our GI tract. It wasn’t until recent years that researchers began to seriously consider the impact of GI homeostasis on altered brain functions such as Alzheimer’s disease and autism. Much of the gut microbiota impact on neural function is due to metabolic functions of the microbiota. Nutrients are made available by microbial metabolism that would otherwise not be available for absorption by our bodies. In addition to metabolism, our gut microbiota produces, and cause host cells to produce, molecules such as NOS that act as signaling molecules to local nerves, allowing for a conduit between the brain and the GI tract. Toxins produced by enteric bacteria can also induce signaling through host receptors such as gangliosides. Additionally, enteric pathogens can cause changes to hormone production, thereby altering signaling through the local nerve cells. This is currently a newly developing field and while specific bacterial/gut/nerve interactions have not been identified, microbiome studies have shown that there are definite differences between the gut microbiome profile of healthy people and patients experiencing neurological perturbations.


PMCID: PMC1773471

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