Spinal-nerve stimulation helped rats in a Swiss lab overcome paralysis to walk and climb stairs.

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Rats with a spinal-cord injury that left their hind legs paralyzed learned to walk again on their own after an intensive training course that included electrical stimulation of the brain and the spine, scientists reported Thursday.

Researchers have known that stimulation and training can improve muscle control somewhat after such injuries in animals. Last year, an international team of scientists reported the case of a 23-year-old paraplegic who regained the ability to stand for a few minutes at a time after a similar program.

But the new study is the most comprehensive and rigorous presentation of what is possible in recovering from such injuries, and the Swiss research team is working on technology to test the techniques in humans.

The report, published online Thursday in the journal Science, demonstrates what, until recently, few scientists thought possible: complete rehabilitation after a disabling blow to the spinal cord. After weeks of training, many rats could walk as well as before the injury, and some could run.

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The findings do not apply to all spinal injuries. The animals’ spinal columns were cut without being completely severed; there were some nerve connections that extended through the injured area. But this is also the case for a substantial proportion — perhaps one-quarter to one-third — of people whose injuries are severe enough to confine them to a wheelchair.

“This is a very exciting study, and my first thought is that it is a proof of principle for treating spinal-cord injuries from a wide variety of conditions, including cancer and even multiple sclerosis,” said Dr. Vineeta Singh, a neurologist at San Francisco General Hospital and the University of California, San Francisco, who was not involved in the study.

A research team led by Gregoire Courtine of the University of Zurich and the Swiss Federal Institute of Technology gave 10 rats the same surgical injury, cutting all direct nerve connections to the hind legs but stopping short of severing the spinal cord. The rats lost the use of their back legs, but not their front legs.

The rats then began a daily regimen. Outfitted with tiny vests, held upright on their back legs but left to bear their full weight, the rats tried to move toward a piece of cheese. They lurched forward like pint-size furry paratroopers, unsteady on their feet after a hard landing.

The scientists provided stimulation in three places: electrically, in the motor area of the brain and in the spinal cord below the injury, and chemically, infusing the wound area with drugs thought to promote growth.

And growth is what they got. After two to three weeks of 30-minute daily sessions, the rats began to take their first voluntary steps. After six weeks, all of the rats could walk on their own, and some could run and climb stairs.

A comparison group of rats that trained more passively on a treadmill did not recover nearly as well. Voluntary motion — hard work combined with sustained stimulation — was necessary for the brain to re-establish command over the limbs.

In effect, Courtine said in a telephone interview, the training forces the brain to recruit what is left of the neural system to get the job done. Neurons sprout like seedlings when they are seeking new connections, and the scientists found increases of 300 percent and more in projections in the brain stem and around the injury, evidence that the nervous system was remapping its connections.

Courtine’s group has demonstrated such recoveries in some 100 rats and is developing technology for a human trial.

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