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Researchers are developing a new way to bypass spinal cord injuries to reconnect nerve communication to the brain. This ScienCentral report investigates whether the technique can restore movement in people with paralysis.
Bridging the Gap
Henry Stifel travels a lot. He also likes to scuba dive and ski. You may be surprised to hear that he does it all despite a spinal cord injury that left him paralyzed more than 20 years ago. “Like anyone else I want to lead as normal a life as possible,” says Stifel. “But I definitely have to think about how I’m going to get from point A to point B in a much more detailed way than anyone else.”
Stifel can move some of his arms and torso, but damage near the top of his spinal cord prevents nerve signals from traveling to the rest of his body. Researchers like neuroscientist John Martin at Columbia University are investigating how to get nerve impulses beyond that barrier. Martin is engineering a nerve fiber bridge to bypass a spinal cord injury so nerve impulses can continue to their intended destinations. Martin says this bypass is a new nerve circuit that he and his colleagues are trying to engineer and insert into the spinal cord as a detour around the damage. “This approach, at this point in our research, is geared toward promoting motor control functions, walking, bladder control, that sort of thing,” says Martin. “We think our bypass approach can offer targeted control of groups of spinal cord neurons that in turn control groups of muscles.”
Small Steps
We move thanks to a complex system of nerves that transmit chemical messages back and forth between the brain and the rest of the body. The spinal cord, roughly the width of a pinky finger, is the central hub for these signals controlling movement and sensation. “The spinal cord can be bruised very easily,” Martin explains. “ And this results in the death of nerve cells at the site of the bruising.” In an adult, nerve cells in the spinal cord will not regenerate on their own, which accounts for the 250,000 people who suffer from chronic spinal cord injuries in the U.S. Martin says most research today focuses on regenerating nerve cells to fix the damaged areas, but this method would most likely to work only within the first days after the injury occurs.
Studying rats, Martin’s research team of Lucal Campos, Zhuo Meng, Guoli Hu, David Chiu and Richard Ambron, took a segment of nerve fiber from an abdominal region, which has many redundant nerves. They grafted this fiber into the spinal cord, attaching it at points just above and just below the spinal injury. “There’s something special about axons outside of the central nervous system, where they can form new connections,” explains Martin. So they waited to see if the newly inserted cells would form connections with the cells in the spinal cord.
The nerve signals followed Martin's detour around the damage.
As little as four weeks later, Martin was able to stimulate impulses to pass through the insertion site to trigger contractions in muscles otherwise paralyzed. “We think that enough information can travel across this bridge to have a significant impact,” says Martin. “But if we’re going to do this in people, we need a more fundamental understanding of why the regenerating axons are forming connections, and with what kind of spinal cord neurons.” Martin hopes to start human testing in about five years.
Neurosurgeon James Guest of the University of Miami says that there is a big jump from rats to humans in terms of understanding how the nerve connections form. “They had a growth on the nerve that was on the order of two millimeters,” explains Guest. “But to get a similar result in a human, you would need to increase that distance of regeneration by about a factor of ten, so it’s hard to know whether in a human you would see similar results.”
But Henry Stifel is optimistic. He says, “Bridging type research is very exciting to me. It’s research that I want to see get to the next level.” In the meantime, Stifel says he will continue to exercise and stay as healthy as possible to be prepared for any sort of medical breakthrough that would give him a chance to get out of his wheelchair.
This research was published in The Journal of Neuroscience, March 3, 2004. It was funded by the New York State spinal cord injury board and the Christopher Reeve Paralysis Foundation.
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