A new study led by the University of Pennsylvania has found that certain species of gut-dwelling bacteria activate nerves in the gut that promote the desire for mice to engage in physical activity. Through a series of controlled experiments, the experts identified the gut-to-brain pathway which explains why some bacteria boost exercise performance.
By recording the genome sequences, gut bacterial species, bloodstream metabolites, and other data for a large number of genetically diverse lab mice, the scientists found that differences in running performances were largely caused by the presence of certain gut bacterial species – particularly Eubacterium rectale and Coprococcus eutactus – in the higher-performing animals. These effects appeared to be triggered by small molecules called metabolites that the bacteria produce, which stimulate sensory nerves in the gut to increase activity in a motivation-controlling brain region during exercise.
The researchers analyzed the collected data using machine learning algorithms to identify attributes of the mice which could best explain the animals’ significant inter-individual differences in running performance. The investigation revealed that genetics accounted for only a surprisingly small portion of these performance differences, whereas differences in gut bacterial populations seemed to play a much larger role. In fact, they noticed that giving mice broad-spectrum antibiotics to annihilate their gut bacteria reduced their running performance by half.
Among the vast population of gut bacteria, two species – Eubacterium rectale and Coprococcus eutactus – stood out, which both produce metabolites known as fatty acid amines (FAAs) that stimulate the CB1 endocannabinoid receptors on gut-embedded sensory nerves connecting the brain via the spine. The stimulation of these receptors causes an increase in dopamine levels during exercise, in a brain area called the ventral striatum – a critical node in the brain’s reward and motivation network.
“This gut-to-brain motivation pathway might have evolved to connect nutrient availability and the state of the gut bacterial population to the readiness to engage in prolonged physical activity,” explained study co-author J. Nicholas Betley, an associate professor of Biology at the University of Pennsylvania. “This line of research could develop into a whole new branch of exercise physiology.”
“If we can confirm the presence of a similar pathway in humans, it could offer an effective way to boost people’s levels of exercise to improve public health generally,” added study senior author Christoph Thaiss, an assistant professor of Microbiology at the same university.
Besides offering cheap, safe, diet-based methods of getting people to exercise and optimizing elite athletes’ performance, further explorations of this pathway may help boost motivation and mood in psychological disturbances such as addiction or depression.
The study is published in the journal Nature.
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