A STEP BEYOND PARALYSIS

By Christine Gorman

The experiment was brutally simple. Scientists from the Karolinska Institute in Sweden took 23 rats and neatly severed their spinal cords, paralyzing their hind legs. Then they took some of the injured rats and set about trying to repair the damage, using microsurgery to build hair-thin "bridges" across the spinal gap. It was an approach other scientists had tried in various forms for nearly 30 years, with little success. But this time, according to a report published last week in Science, it worked. Not only did the severed nerve fibers grow across the bridge, but the rats also began to regain function in their lifeless limbs.

The study, which was immediately hailed by other scientists as "audacious" and a "tour de force," sent a shiver of hope through thousands of paralyzed people. Although doctors quickly pointed out that it may be years before last week's findings could be turned into an effective therapy, they too were clearly buoyed. In a companion commentary, New York University neuroscientist Dr. Wise Young wrote, "The possibility of effective regenerative therapies for human spinal cord injury is no longer a speculation but a realistic goal."

The Karolinska team members, led by Henrich Cheng, took special pains to avoid the pitfalls that had tripped up investigators in the past. They widened the gap (by removing a quarter inch of spine) to ensure that no nerve tissue remained to produce false-positive results. Then they built their cellular bridges according to a precise blueprint that carefully distinguished between the two kinds of nerve tissue in the spinal cord--white and gray matter. White matter contains the parts of nerves that are surrounded by a substance called myelin, which acts like insulation around an electric wire. Gray matter contains the parts that have no insulating myelin. It's almost impossible to get regeneration in white matter. Growth in gray matter, on the other hand, is relatively easy to stimulate.

Using nerves from the rat's chest muscles for the bridge, Cheng carefully connected the insulated white matter on one side of the spinal cord to uninsulated gray matter on the other. That way, the nerves in the gray matter would grow toward the white and, he hoped, re-establish contact. The investigators used a natural adhesive called fibrin to anchor the bridge in place.

Then they waited. Not much happened for the first three months, as the animals dragged their back legs. Then one day, a few of them started to flex their hind muscles. Awkwardly at first, and then with growing strength, they began to crawl around. A year later, they could support their weight and move their rear legs, although they were still not walking normally.

Much remains to be done before paraplegics can think about rising out of their wheelchair. Most spinal injuries in people occur when the cord is crushed, not severed, so it's not yet clear how this advance could be applied to them. What is important, however, is that Dr. Cheng and his colleagues have demonstrated that there are no fundamental biological barriers to repairing damaged spinal cords. And that's a big step forward.

--By Christine Gorman. Reported by Alice Park/New York

With reporting by Alice Park/New York