Wednesday, December 16, 2009

Why Exercise Makes You Less Anxious


NYTimes:
Scientists have known for some time that exercise stimulates the creation of new brain cells (neurons) but not how, precisely, these neurons might be functionally different from other brain cells.

Researchers at Princeton University recently made a remarkable discovery about the brains of rats that exercise. In the experiment, preliminary results of which were presented last month at the annual meeting of the Society for Neuroscience in Chicago, scientists allowed one group of rats to run. Another set of rodents was not allowed to exercise. Then all of the rats swam in cold water, which they don’t like to do.They found that the stress of the swimming activated neurons in all of the brains. The researchers could tell which neurons were activated because the cells expressed specific genes in response to the stress. But the youngest brain cells in the running rats, the cells that the scientists assumed were created by running, were less likely to express the genes. They generally remained quiet. The “cells born from running,” the researchers concluded, appeared to have been “specifically buffered from exposure to a stressful experience.” The rats had created, through running, a brain that seemed biochemically, molecularly, calm.


“It looks more and more like the positive stress of exercise prepares cells and structures and pathways within the brain so that they’re more equipped to handle stress in other forms,” says Michael Hopkins, a graduate student affiliated with the Neurobiology of Learning and Memory Laboratory at Dartmouth


Other researchers have looked at how exercise alters the activity of dopamine, another neurotransmitter in the brain, while still others have concentrated on the antioxidant powers of moderate exercise. Anxiety in rodents and people has been linked with excessive oxidative stress, which can lead to cell death, including in the brain. Moderate exercise, though, appears to dampen the effects of oxidative stress. In an experiment led by researchers at the University of Houston and reported at the Society for Neuroscience meeting, rats whose oxidative-stress levels had been artificially increased with injections of certain chemicals were extremely anxious when faced with unfamiliar terrain during laboratory testing. But rats that had exercised, even if they had received the oxidizing chemical, were relatively nonchalant under stress. When placed in the unfamiliar space, they didn’t run for dark corners and hide, like the unexercised rats. They insouciantly explored.


Dr. Greenwood of the University of Colorado added that it was “not clear how that translates” into an exercise prescription for humans. You may not feel a magical reduction of stress after your first jog, if you haven’t been exercising. But the molecular biochemical changes will begin, Dr. Greenwood says. And eventually, he says, they become “profound.”

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