Improving stamina via exercise depends not only on hard-working muscle cells but on brain-cell activity, too, new research in mice that challenges conventional wisdom reveals.
Without the activity of certain brain cells called neurons, mice fail to show endurance gains no matter how hard they sprint on a treadmill, researchers found.
But when researchers artificially activated the neurons after exercise, the animals gained even more endurance than usual, according to a report in Neuron.
"The idea that muscle remodeling requires the output of these brain neurons is a pretty big surprise," study leader Erik Bloss of The Jackson Laboratory in Bar Harbor, Maine said in a statement.
"It really challenges conventional thinking" that exercise benefits come solely from muscles, he said.
Tracking brain activity in mice during and after running, the researchers found that a particular cluster of neurons in the hypothalamus that express a protein called steroidogenic factor-1 became active for about an hour after mice finished running.
As the mice trained over weeks, more and more SF1 neurons became activated after each exercise session, and connections between the SF1 neurons became stronger and more numerous, the researchers reported.
Animals that exercised had about twice as many connections between these neurons as animals that did not, the researchers also found.
When SF1 neurons were "turned off" for 15 minutes after each training session, the mice stopped improving their endurance and began to fare worse on voluntary run tests.
"If you give a normal mouse access to a running wheel, they will run kilometers at a time," said Bloss. "When we silence these neurons, they effectively don't run at all. They hop on briefly but can't sustain it."
When researchers stimulated SF1 neurons for an hour after treadmill sessions, mice showed enhanced endurance gains and reached higher maximum speeds.
"There's the very real possibility that we can eventually take advantage of this circuit to boost the effects of moderate exercise," said Bloss.
"If we can mimic or enhance exercise-like patterns in the brain, that could be particularly valuable for older adults or people with mobility limitations who can't engage in intensive physical activity but could still benefit from exercise's protective effects on the brain and body."
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