Canadian scientists say they have fitted a plastic tube - made from the same sort of material used in soft contact lenses - around the spinal cords of paralyzed rats and have seen some movement restored.
The rats, whose spinal cords had been cut, walked somewhat better eight weeks after a plastic tube filled with chemicals that promote nerve growth was implanted in their spines.
"We know that the rats improved. What we have to do now is figure out how significant the improvement is," said Molly Shoichet, an associate professor of chemical engineering and applied chemistry at the University of Toronto. She presented her research Tuesday before the annual meeting of the American Chemical Society in Chicago.
Shoichet, who has so far studied 80 rats using the technique, stressed that much more work needs to be done with animals before the treatment can be tested on people.
The tubes, five millimeters in length, fit snugly around the injured area of the spine and act as a bridge to connect damaged nerves. Designed to mimic the flexibility of the spinal cord, the tube acts as a pathway for the nerves to grow.
While most damaged nerve cells regenerate quickly after an injury, spinal cord nerves behave differently, sustaining secondary injuries from the body's immune response and in some cases destroying themselves. So the nerve cells have to be coaxed into growing.
A number of researchers have had some success in getting bundles of nerve cells in paralyzed rats to regrow, using injections or genetically modified cells to deliver growth factors to the injury site. Shoichet's group is the first to try to create an artificial environment in a growth-factor-filled tube that attempts to replicate the properties of the spinal cord.
Shoichet and her colleagues use a common test of paralysis that is scored from 1 (complete paralysis) to21 (normal movement) to evaluate rats in the study. Rats that were injured and untreated were scored at 2; those treated with the chemical-filled tubes scored between 8 and 11, depending on the growth factors used.
"We saw some directed nerve tissue growth along the plastic tube, but we do not yet know if the severed nerves were connected to the newly grown tissue," Soichet said. "We hope that once axons (the key nerve cells) grow across the (injury) gap, they will make the appropriate connections."
Not only must axons grow to work again, they also must make connections to neighboring target cells.
Spinal cord injuries once were almost always fatal. Today about 90 percent of people who sustain spinal cord injuries survive and live near-normal life spans.
According to the Christopher Reeve Paralysis Foundation, 250,000 to 400,000 U.S. residents are living with spinal cord injury, and an average of 11,000 new injuries take place each year.
As recently as a decade ago, doctors could do little for spinal injury patients but realign and then immobilize the damaged spinal column. The steroid drug methylprednisolone, approved in 1990, has helped Reeve and thousands of others limit secondary damage to the nerves when given within a few hours of the initial injury.
Major advances have been made in managed rehabilitation after an injury, and the National Institute of Neurological Disease and Stroke reports that most patients who survive spinal injury naturally regain some function within six months.
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