What is the gut-brain connection?
How the gut and brain are interconnected and why they impact each other's functions.
Key Takeaways
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The gut-brain connection, commonly referred to as the gut-brain axis, is the studied bidirectional communication between the central and the enteric nervous system. The central nervous system (CNS) being the brain and spinal cord and the enteric nervous system (ENS) is the intrinsic nervous system that controls the GI tract. The ENS that regulates our gut is often called the body's “second brain.” Although it can't compose poetry or solve chemical equations, this extensive network uses the same chemicals and cells as the brain to help us digest and to alert the brain when something is amiss.
This gut/brain connection links the emotional and cognitive centers of the brain with gastetointestinal tract. Recent studies have described the importance of the gut microbiota in influencing these interactions.
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Braak’s Hypothesis
Neurologists have dug deeper into the connection between the gut and the brain, conducting studies with compelling results.
Braak's hypothesis is a hypothesis generated by German neurologist Heiko Braak which was subsequently published in a study conducted by Braak and other colleagues in 2003. The hypothesis states that Parkinson's Disease begins in the gut, and then travels up to the brain through the vagus nerve. Environmental and genetic factors contribute to inflammation in the gut, reducing the number of beneficial microbes and short-chain fatty acids. This inflammation fosters an environment in which pathogens can thrive. Once it spreads through the GI tract and finds the vagus nerve, these harmful pathogens travel up to the brain, causing neurodegeneration and the cognitive symptoms seen in Parkinson's patients.
Figure 1. A schematic representation of the Braak’s hypothesis of Parkinson’s disease (PD). Microbial products come into contact with olfactory and/or enteric neurons, which trigger the aggregation of α-Synuclein (1 and 2). The aggregated α-Synuclein spreads toward the central nervous system via the olfactory bulb and the vagus nerve (3 and 4). Eventually, the aggregated α-Synuclein arrives at the substantia nigra (5). Genetic factors are likely to contribute to PD, but the exact mechanism remains to be elucidated (6).
Image Courtesty of Frontiers in Neurology
Study: Fiber-Rich Diet Affects Microglial Function in a-Synuclein Overexpessing Mice
Another noteworthy study explores this hypothesis by using mice to see how a fiber-rich diet impacts microglial function in a-synuclein overexpressing mice, a preclinical model with PD-like symptoms and pathology. The study, which was conducted by Dr. Reem Abdel-Haq, among others, concluded that a prebiotic diet reduced the motor symptoms and a-synuclein aggregation in the brain that are associated with neurological diseases.