Mice are human too. Some are couch potatoes, others are exercise addicts. Why is that? Apparently not in the genes. Researchers led by Lenka Dohnalová from the University of Pennsylvania found this out. They left 199 as genetically diverse as possible Laboratory mice run on treadmills as much (or as little) as they want. Some mice voluntarily traveled more than 20 kilometers a day. For each mouse, they recorded 10,500 data points, from mileage to metabolic parameters to genetic material.
Genetic variations could only explain a small part of the different training zeal. The research team only found a hot lead when they had the data evaluated by self-learning algorithms. The astonishing result: The factor that was statistically best able to predict the mice’s enthusiasm for sports was the composition of the intestinal flora. Above all, the distribution of the two bacterial strains Eubacterium rectale and Coprococcus eutactus correlated strongly with the desire to run. The researchers published their results in the journal “Nature”.
The lust of mice to run
However, since a correlation is not causality, the scientists determined the connection with numerous other experiments. For example, if they killed the intestinal flora of athletic mice with antibiotics, their urge to move was reduced. If, on the other hand, they transplanted the stool from athletic mice to sedentary mice, these too discovered their love of running. Remarkably, the overall physical fitness and normal movement behavior of the mice, such as walking around the cage, were unaffected.
The researchers got to the bottom of the underlying mechanism with detective flair. More than a dozen laboratories have been involved over several years. According to their findings, the signal path from the gut to the brain works as follows: the microbes in the gut produce certain metabolic products such as fatty acid amides during physical activity. Some of these are chemically closely related to cannabis compounds and dock to the same receptors. In doing so, they stimulate certain nerve cells in the gut that connect via the spinal cord to the striatum – a region in the cerebrum responsible for motivation and reward. There, the signals from the intestine slow down the release of an enzyme that breaks down dopamine. In other words, mice with the “right” microbiome experience a dopamine rush from running that appears to be comparable to the “runner’s high” reported by many endurance athletes. Mice without these gut microbes experience exercise as less rewarding and are correspondingly less motivated.
Effect of the “runner’s high”
The evolutionary purpose of this mechanism may be “to link food availability and gut microbiota status to the willingness and ability for sustained physical activity,” the paper states. The researchers were also able to observe the pain-reducing effect of the “runner’s high” in their test animals. “This could indicate that the signaling pathway we discovered also regulates other aspects of exercise physiology,” the researchers write. “Other behaviors that depend on striatal dopamine levels may also be modifiable with lifestyle changes, diet, or supplements.” The approach can also help with addictions or depression, says co-author J. Nicholas Betley, biology professor at the University of Pennsylvania.
“If these findings can be extrapolated to humans, they raise the question of whether gut bacteria can influence the mental processes surrounding the decision to exercise,” comment neuroscientists Gulistan Agirman and Elaine Y. Hsiao of the University of California in Los Angeles who were not involved in the research.
Research work in recent years has shown time and again that there is also a direct connection between the brain and the intestines in humans and that its inhabitants play a decisive role in this. The microbiome influences aging, the immune system, hormone balance and depression, among other things.
(grh)
