Injuries to the central nervous system in humans are particularly devastating because damaged nerve fibers in adults do not regenerate on their own.
The growth in the rats enabled them to recover their ability to function to "an amazing degree," said Martin Schwab of the Institute for Brain Research at the University of Zurich in Switzerland.
"If you test these animals for hand function, precision movements, you find a recovery of the behavior which is almost 100 percent," he said.
The study by Schwab and his colleagues at the university appears in the June issue of the journal Nature Neuroscience. Details were released Monday.
Story Landis, scientific director of the National Institute of Neurological Disorders and Stroke, part of the National Institutes of Health, was impressed by the findings.
"This should definitely be tested in primates," she said. "What makes it promising is they've shown a remarkable regrowth of axons [nerve fibers], sprouting of axons, and functional recovery."
The researchers cut through nerve fibers in the rats' brainstems, where the upper part of the spinal cord joins the front of the brain. That knocked out fine motor control of the animals' front limbs. In humans, the corresponding area controls such movements as typing on a keyboard.
Regeneration of brain and spinal cord nerves is naturally inhibited by proteins in the protective sheaths of the nerve fibers. So Schwab and his colleagues devised an approach to neutralize the proteins with a specially engineered antibody, IN-1.
Rats injected with IN-1 sprouted healthy, new nerve fibers in undamaged regions of their brains and spinal cords that took over for the damaged ones.
The nerves sprouted and built new connections "which automatically seem to be the right connections," Schwab said.
Damaged fibers also showed some regeneration.
The ability of the antibody to promote new compensatory growth rather than just repair damaged nerve fibers could help in treating stroke, researchers said. Strokes tend to damage one side of the brain.
The human central nervous system contains growth inhibitors similar to those found in rats. Schwab already is collaborating with a large biotechnology company to neutralize them with antibodies.
Others were more cautious.
In an editorial, journal editor Charles Jennings said it is difficult to know if animal results with IN-1 will speed up progress in spinal cord repair: "The new findings suggest that the picture is not likely to be simple."
Written By Jane E. Allen