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Potential new treatment for paralysis?

It seems like something out of science fiction: People paralyzed from a motorcycle or other accident are suddenly able to walk again when doctors jolt their spinal cord with electricity. Now, scientists have pinpointed the nerve cell population that’s responsible—at least in injured mice—potentially opening the door to new treatments for paralysis.

A bad fall or car accident can sever nerve connections in the spinal cord, cutting off the circuitry that allows people to control various parts of their body. But some connections remain. Zapping these with electricity—by surgically implanting a bundle of electrodes into the lower spinal cord—in combination with physical therapy and rehab can restore limb movement, bowel and bladder function, and even sexual activity.

But neither doctors nor scientists are clear on why or how the approach works. So in the new study, neuroscientist Grégoire Courtine at the Swiss Federal Institute of Technology, Lausanne, and his colleagues tracked nine spinal paralysis patients through a 5-month program of electrical stimulation, exercise, and rehab. With electrical stimulation, all nine regained their ability to walk unassisted.

The team obtained images depicting nerve cell activity in the spinal cord of these people while walking, both before and after undergoing treatment. Surprisingly, after treatment, the spinal cords of these individuals showed less activity than before. This suggested that perhaps only a subset of neurons was being activated during stimulation to help patients recover.

To get a better sense of what was going on, the team repeated the study—but this time on mice whose spinal cords had been injured. At different points throughout the therapy, which included mice walking on a treadmill with support and electrical stimulation, the researchers determined which genes are activated in specific populations of nerve cells across the spinal cord, creating a diagram based on the cells’ locations. They then used a computer program to determine which nerve cell populations were most important during the recovery process. A specific subpopulation of neurons in the mouse spinal cord, which express two markers called Vsx2 and Hoxa10, was activated after electrical stimulation, the team reports in Nature.

To verify that these neurons are essential to recovery, the researchers selectively manipulated their activity in mice. When the scientists activated this population of neurons, the mice recovered their ability to walk. When they blocked these cells during stimulation, the mice did not. Blocking the activity of the cells in healthy mice did not affect their ability to walk, the team found, suggesting these cells become crucial for recovery after spinal cord injury.

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