Ellen Phiddian
Cosmos science journalist
Scientists have isolated a chemical in mouse brains that mediates the decision to eat or exercise.
The chemical orexin, which also mediates sleep, prompted mice to choose exercise over a snack more frequently.
The Swiss researchers say that their findings could help to advance research in promoting exercise among humans.
The team has published its research in Nature Neuroscience.
According to the World Health Organization, 31% of adults and 80% of adolescents are not getting enough physical activity. The WHO recommends at least 150-300 minutes per week for adults, and 60 minutes per day for children and adolescents.
“Despite these statistics, many people manage to resist the constantly present temptations and get enough exercise,” says study co-author Professor Denis Burdakov, a neuroscientist at ETH Zurich, Switzerland.
“In neuroscience, dopamine is a popular explanation for why we choose to do some things but avoid others.
“However, our current knowledge about dopamine does not easily explain why we decide to exercise instead of eating.
“Our brain releases dopamine both when we eat and when we exercise, which does not explain why we choose one over the other.”
The researchers placed mice in 10-minute trials where they had 8 different activities to choose from. One of these activities was a running wheel, and another was a “milkshake bar” where they could drink a strawberry milkshake.
“Mice like a milkshake for the same reason people do: it contains lots of sugar and fat and tastes good,” says Burdakov.
Some of the mice tested had their orexin systems blocked through a drug or genetic modification.
Mice with ordinary orexin systems spent twice as much time on the running wheel, and half the time at the milkshake bar, compared to orexin-blocked mice.
But in a second experiment, where mice were presented with a choice between just 2 activities – wheel or milkshake – orexin didn’t make a difference.
“This means that the primary role of the orexin system is not to control how much the mice move or how much they eat,” says Burdakov.
“Rather, it seems central to making the decision between one and the other, when both options are available.”
The researchers are now interested in verifying their results in humans, which they think is likely since the brain functions here are very similar to mice.
About 1 in 2,000 people have genetic conditions that restrict their orexin systems, which causes the sleeping disorder narcolepsy. Conversely, some people with insomnia are prescribed drugs that block orexin. Both of these populations may be helpful for studying the effect in people.
