In what one scientist called a tour de force, a group of researchers in Sweden has succeeded for the first time in growing nerve cells across gaps in severed spinal cords in rats.
The work is startling and demands to be repeated by others, said experts in the field, who noted that some previous reports of similar achievements had failed to pan out. It is merely the first step toward the distant goal of curing patients with injured spinal cords, they said, but the work shows that such a goal may not be an impossible dream.
The study, by Dr. Lars Olson, a professor of neurobiology; Dr. Henrich Cheng, a neurosurgeon; and Dr. Yihai Cao, a molecular biologist, at the Karolinska Institute in Sweden, is being published today in the journal Science. It involved adult rats whose spinal cords were completely severed, leaving a gap of about one-fifth of an inch.
Using delicate microsurgery, Cheng sewed a bridge of slender nerve cells across the gap, to guide the severed nerves in their attempt to regenerate. He obtained the nerves for the bridge from the animals’ chests.
The investigators glued the bridge down at either end with fibrin, the sticky substance in blood that shows up on a wound just before a scab forms. They had first mixed the fibrin with fibroblast growth factor, a substance that encourages cells to grow.
Then they watched for three months while the injured animals dragged their hind legs behind them, like dead weights. Finally, Olson said, he noticed a change in the animals that had gotten the complete repair treatment, but not in control animals that had had no surgery or only parts of it. The treated animals, he said, started to flex their legs.
Olson, who had been working on spinal cord repair for almost three decades, said, “That was one of the best moments in my scientific life.”
As time went by, he said, the rats continued to improve. “They started to move their hind limbs, as if they were attempting to use them for walking,” Olson said.
A year after the surgery, the treated animals could partly support their weight and could move their legs, although they were not walking normally. When the researchers did anatomical studies, injecting dyes into the nerve tracts after the rats had been killed, they found that nerves had regrown from either end of the injury, growing down to the tail and up to the brain.
Dr. Jerry Silver, a professor of neuroscience at Case Western Reserve University in Cleveland, said he was taken aback by the results.
In cutting away a large section of the rats’ spinal cords, he said, “they’ve done about the worst thing to a spinal cord that you can do,” Silver said. “The model is rather dramatic. They’ve duplicated the worst thing possible and then some.”
And then, Silver said, the investigators did what many thought was impossible - they got the nerves to regenerate across the gap and to function again. “I think it’s pretty incredible,” Silver said.
Dr. Wise Young, a professor of neurosurgery, physiology and neuroscience at New York University, who wrote an accompanying editorial in Science, also was impressed.
“I think this paper shows not only that regeneration is possible but it also shows that the task will be easier than we ever anticipated,” he said. “Probably very few axons crossed the gap, probably no more than 10 percent,” he said. And that means, Young said, that “we don’t have to regrow the whole spinal cord.” It means, he said, that repairing spinal cord injury “is in the realm of possibility.”