An international team of researchers has enabled paralyzed rats to walk again, raising hopes that someday, human victims of paralysis might also have their mobility restored.
The ground-breaking experiment involved eight rats whose spines had been severed, leaving them completely paralyzed.
Using a combination of three treatment strategies - electrical stimulation, doses of the spinal-nerve-activating drug serotonin, and treadmill exercise - researchers say all the rats regained the capacity to walk, although not voluntarily.
Previous experiments have shown that there is a natural circuit of nerves in the mammalian spine that can, without any brain input, be activated to move legs in patients with spinal-cord injuries. But none of the remedial measures, drugs, electrical current or exercise, has worked by itself to enable paralyzed patients to walk again.
The results using all three treatments were stunning, according to lead researcher Gregoire Courtine of the University of Zurich in Switzerland.
"These animals [that were completely] paralyzed could regain the capacity to walk with full weight bearing, to walk at different speeds, even run, to walk backwards, walk even sideways," said Gregoire Courtine.
Courtine says the rats' legs began to move within a week of therapy, and maximum movement occurred within several weeks, although the animals were never able to move their limbs voluntarily without external electrical stimulation.
Susan Howley is executive vice president for research at the Christopher Reeve Foundation, an organization devoted to finding a cure for paralysis, and which helped fund Courtine's research.
"Many others in the field were very excited by this study which really does break new ground in that these animals, whose cords were completely transected, were fully weight-bearing on a treadmill," said Susan Howley.
Howley says all of the measures used on the rats - electrical stimulation, seratonin drugs and weight-bearing exercise - are readily available now.
"So I think the component parts are such that you can imagine [that] translating it to a human patient might not be a big hurdle [difficult] at all," she said.
But before the therapy could be used to help spinal cord injured patients walk again, researcher Gregoire Courtine says a device or prosthetic would have to be developed to deliver the stimulation to intact nerves below where the spine was injured.
"The next step is to develop prosthetic interfaces," said Courtine. "This means electrode arrays [multiple wires] that we can implant chronically [for a long time] over the extent of the spinal cord injury, to enable multi-site stimulation."
Courtine says researchers are working on an electronic prosthetic for paralyzed human patients, but such a device is likely several years away.
The paper describing the restoration of leg movements to paralyzed rats was published this week in the journal Nature Neuroscience.