Recent studies at the University of Pennsylvania reveal how specific bacteria found within our gut may be responsible for determining how much we want to exercise. The gut microbiome and dopamine neurotransmitters released in the brain are connected through the spine to create a reward system for physical activity, as evidenced in studies observing mouse exercise behavior and their gut microbiota.
To conduct these experiments, scientists observed how often randomly-selected mice subjects ran on a wheel, as well as how long they could run on a treadmill. These mice were tested for a variety of factors, though scientists found that the presence of two bacterial species in their gut—Coprococcus eutactus and Eubacterium rectale—were consistent among “fit” mice (those that were more willing to run and could run for longer periods of time) compared to “unfit” mice. The existence of these bacterial species was more likely to determine exercise motivation than genetic differences. To solidify this connection, they gave the mice antibiotics to eliminate all gut bacteria. This caused the antibiotic-treated mice to exhaust faster and run less frequently than mice who did not have an impaired microbiome, further reinforcing the significance of these bacterial species in exercise motivation.
Antibiotics caused decreased exercise motivation in mice
Image Source: James Brey
Specifically, scientists discovered that the bacterial species Coprococcus eutactus and Eubacterium rectale produce molecules called fatty acid amides (FAAs). After they are released, FAAs then engage with CB1 endocannabinoid receptors that reside on sensory nerves located in the gut itself. These sensory nerves are directly linked to the brain through the mouse’s spinal cord. When stimulated, the nerve initiates the release of dopamine, a neurotransmitter that boosts mood and creates a reward system when certain actions are repeated, in the brain. This network of neural pathways occurs in a region of the brain called the ventral striatum, which is specifically responsible for activating motivation and reward systems.
These findings may appear evolutionary counterintuitive at first, though it is hypothesized that the pathway could have originated because the presence of specific nutrients in the environment helps inform the makeup of one’s gut microbiota. In other words, the type of bacteria that lives in your gut is influenced by environmental factors. Gut microbes can therefore communicate with the brain through neural pathways along the spine to signal whether an individual has the capacity to exercise or needs to conserve energy based on the available nutrients that they ingest.
Though this study was conducted on mice and not humans, it still has relevant implications for how these neural pathways and gut microbiota can be influenced to maximize our exercise motivation and elevate our overall health. For example, diets can be supplemented with FAA-containing ingredients such as plant oils (particularly sesame, soybean, and peanut oils), or prebiotics and probiotics that improve overall gut health to enhance the production of FAAs. Now that the baseline connection has been confirmed in mice, further studies can be conducted to determine how the network between gut bacteria and dopamine release can be utilized for human medicine and health research.
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