The Simplified Guide to the Gut Brain Axis – How the Gut and The Brain Talk to Each Other

The gut-brain axis (GBA) is a bidirectional link between the central nervous system (CNS) and the enteric nervous system (ENS) of the body. It involves direct and indirect pathways between cognitive and emotional centers in the brain with peripheral intestinal functions. The GBA involves complex crosstalk between the endocrine (hypothalamic-pituitary-adrenal axis), immune (cytokine and chemokines), and the autonomic nervous system (ANS).
Within the gut, there are approximately 1014 microorganisms, which is around 10 fold more cells than there are human cells in the human body. Collectively, the genetic material of the microbiome is approximately 150 times greater than the human genome, which has led some scientists to label the microbiome as a ‘superorganism’.
The Gut Microbiota interacts with the brain through several mechanisms. These include interaction with enteroendocrine cells resulting in the production of neuropeptides (5 HT, CCK, PPY), activation of immune cells to produce cytokines, production of microbial metabolites, and activation of vagus nerve all of which can influence brain physiology impacting neurotransmission, neurogenesis, and neuroinflammation. Stress, on the other hand, activates the limbic system which can influence gut physiology through descending nervous system projections which synapse on the gut mucosa. This, in turn, can alter microbiome composition. This intricate network thus exerts effects that alter both GI and brain function.