The study, conducted in rats, suggests that nerve cells can be inserted and stimulated to grow through damaged areas of the spinal cord, perhaps leading to better treatments for spinal cord injury. The research is part of a wave of studies challenging the conventional wisdom that severed nerves in the spinal cord are nearly impossible to regenerate. The study appears in the October issue of the Journal of Neurotrauma.
Dr. Vernon Lin, professor of physical medicine at UCI and director of the Spinal Cord Injury Group at the Long Beach V.A., and his colleagues found that grafting nerves from the rib cage and adding the growth stimulator, a molecule called aFGF, partially restored hind leg movement in rats that had their spinal cords severed.
"By using tiny nerves from the rib cage as cables connecting the severed spinal cord, we were able to get some improvement in leg function," Lin said. "Regeneration is considered very difficult because the damaged area apparently inhibits growth of new nerve-cell connections. This study gets us closer to arriving at the right combination of growth factors, nerve cells and physical stimulation that overcome these inhibitions and successfully treat spinal cord injury."
Lin and his team found that 12 rats with severed spinal cords were able to move their hind legs again after treatment with both the aFGF and the nerve grafts, while rats that had either the aFGF or nerve grafts alone showed nearly no improvement. Rats receiving both the growth factor and the nerve cell grafts could support some of their weight on their back legs.
The growth factor aFGF is normally produced in the spinal cord by nerve cells, but scientists suspect that it is stored and only used when nerve cells are damaged. Previous studies have shown that adding aFGF can stimulate growth in individual nerve cells in the laboratory.
The rats' movements were measured using a tool called a BBB score. Normal movement rates a BBB score of about 21. Six months after the rats were treated, the animals that received the aFGF and nerve grafts had scores between six and seven. The other animals did not score higher than one on the scale.
"While not a perfectly normal score of locomotion, the treatments did allow the rats to step forward and put weight on their hind legs," Lin said. "We also found that the nerves in the leg below the injury site were once again receiving nerve impulses from the brain. We believe that eventually, we may be able to find the right mix of factors and physical stimulation all working together to improve this restored movement to more normal levels."
The researchers also plan to study the use of robots to aid in the placement and maintenance of nerve cells that are grafted into an injured area, to help improve movement. They recently received a $600,000 research grant from the Veterans Administration to continue their work in designing and testing robots that could help in maintaining the gait necessary to walk. Currently, they are testing the ability of the robots to accurately maintain a walking gait in rats. Eventually, the researchers hope to test the robots in humans and determine if the machines are actually helping restore the ability to walk after spinal cord injury.
Lin's colleagues in the study include Yu-Shang Lee of UCI's College of Medicine and Ian Hsiao of UCI and the Long Beach V.A. Medical Center.
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Journal
Journal of Neurotrauma