Wearing a robotic harness, paralyzed rats have been made to walk again, according to a new study—albeit with an oddly upright, humanlike gait and while stimulated by judicious jolts of electricity and chemicals.

It's the first time severely injured spinal cords have been reawakened, say researchers, who add that the technique might hold some promise for disabled people.

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First, neuroscientist Grégoire Courtine and his team severed the spines of 27 rats, leaving some tissue intact but no direct nerve connections—and therefore no way for the animals to control their hind legs.

A week later the researchers put 17 of the rats on a sort of physical therapy regimen and began administering chemical injections and electric stimulation directly to the rodents' spinal cords. The remaining ten rats, used as a control group, received no treatment. (Also see "Stem Cells Repair Damaged Spinal Cords in Mice.")

The physical training began on a treadmill, with the 17 rats using a robotic harness—created especially for the study—that suspended the animals upright but did not propel them forward.

The treadmill exercise exploited reflexes that make walking in some ways passive, explained neuroscientist Naomi Kleitman of the U.S. National Institutes of Health (NIH).

"Imagine you can't get any signals from your brain to below the injury—you can still walk on a treadmill," said Kleitman, who wasn't part of the new study.

"The treadmill is dragging my right foot behind me," she added. "That will stimulate a reflex in my left leg that will make my left leg take a step."

Anything for Chocolate?

In addition to the treadmill therapy, the trained rats received mild electrical stimulation—designed to mimic the signals the brain sends to move the legs—and injections of chemicals known to help nerve cells, which carry those signals, to better communicate.

After three weeks of treadmill training, 10 of the 17 rats were encouraged to take steps on a sort of tiny runway—still in the harnesses, though, and still being electrochemically stimulated.

Within a few more weeks—and with the incentive of a bit of chocolate at the end of the course—the runway rats were "sprinting" up stairs in their harnesses, study co-author Courtine said in a statement.

Though the rats still couldn't walk unaided, they had undergone a "nearly complete" regrowth of spinal nerve fibers, reestablishing the severed connections between brain and haunches, the study says. The effect was seen only the rats that had undergone training on solid ground—the untrained and treadmill-only rodents failed to regain voluntary movement in their paralyzed legs.

Hope for People?

All these treatments are already being tested in people, NIH's Kleitman said. What makes the study exciting is that the methods have never before been tried in combination.

The electrochemical cocktail, she said, is what "to me, made this paper quite relevant, even though it's just in rats."

Mayo Clinic neurologist Tony Windebank agreed. "All the things they are doing in rats are things you can do in people."

He cautioned, however, that stimulating and enhancing the automatic walking reflex is "much easier to do in quadrupeds compared to upright animals."

But, he said, "I think it's an important step forward," even if "it's not the giant step for mankind—it's not going to translate to, Let's do this in people next month and have them walking."

Kleitman believes the severity of the rats' paralysis and subsequent recovery should give some people hope.

"Some people might say it's not worth doing anything with" severely paralyzed people, "because there's almost nothing left," she said. "Studies like this one show it's worth trying."