The brain benefits from physical activity in many ways, including boosts to memory, mood, and learning. According to a paper published Thursday (July 9) in Science, it appears possible to transfer those benefits of exercise through blood transplants, at least in mice. The authors point to an enzyme known as glycosylphosphatidylinositol specific phospholipase D1 (Gpld1), produced during exercise, as a likely agent responsible for mice’s improved memory and learning skills after receiving a transfusion from mice that had worked out.

Previous studies have shown that transfusing blood from young mice into older mice conferred a benefit. According to Science, conversations between lead author Saul Villeda of the University of California, San Francisco, and others led them to question whether a similar effect could occur with blood transfusions from active mice into more sedentary ones of the same age.

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“Can your brain think that you exercised, from just something in your blood?” Villeda tells Science.

To test this, older mice were given a wheel on which they ran multiple miles every night. After six weeks of training, the researchers began taking blood from the exercised mice and transfusing it into old mice with no wheel available. After receiving eight infusions per week for three weeks, the inactive mice that received the transfusions developed twice as many neurons in the hippocampus as a control group and performed at nearly the same level on learning and memory tasks as the mice that exercised.

One of the biggest differences in the blood of mice that exercised was a higher abundance of Gpld1, which is made in the liver during physical activity. To see if the same phenomenon exists in humans, the team used FitBits to track the physical activity of elderly people and found that the most active ones had the highest levels of GPLD1, though the study did not include any data on learning and memory with this group.

Down the road, a transfusion model might be able to help people who are unable to exercise due to age or disability, Villeda tells NPR. “One of the best-known interventions that has a benefit on the brain is exercise,” he says. “The problem is many of the elderly are frail. They can’t physically do the exercise.”

Despite the success of being able to pass on exercise benefits to inactive mice, Villeda cautions against thinking that “exercise in a bottle” becoming available anytime soon. There are currently too many unknowns about GPLD1’s effects, he tells NPR. Others have also stressed the importance of managing expectations.

“It’s a long step between identifying this enzyme and, say, making a pill out of that,” Bradley Wise, a neuroscientist and program officer at the National Institute on Aging, which provided funding for the study, tells Science. “This is one piece of the puzzle.”

Clarification (July 13): The story has been edited to note that Bradley Wise's employer funded the study.  

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