Using a totally new approach, researchers at the Massachusetts General Hospital (MGH) have for the first time induced the growth of severed adult mammalian spinal cord fibers across the site of the injury. The animal study appearing in the May issue of Neuron is the first to report repairing such an injury without the use of implanted cells or tissues to bridge the severed fibers. In addition, the findings call into question current assumptions about barriers to spinal cord regeneration.
"We have actually tricked nerve cells into growing beyond the area of a spinal cord injury by switching them into an actively growing state," says Clifford Woolf, M.D., Ph.D., of the Neural Plasticity Research Group in the MGH Department of Anesthesia and Critical Care, who led the study. "While the particular approach we used cannot be applied in humans, it points us in a promising new direction. The question is no longer whether spinal cord regeneration is possible but how it will be achieved."
It has been known for years that severed nerve fibers in the adult spinal cord cannot regenerate. However, damaged peripheral nerves - those in the extremities - can heal themselves. What has intrigued and frustrated researchers is the fact that the fibers making up one sensory system in the spinal cord come from the same cells as do the fibers in peripheral nerves. These sensory nerve cells or neurons have two long processes, called axons, that extend from the main cell body located next to the spinal cord. One axon, the central branch, joins the spinal cord and travels to the brain; the other, the peripheral branch, travels out to the extremities. If the peripheral branch of these cells is injured, it regenerates; if the central branch is injured, it does not.
Because two branches of the same cell exhibit totally different healing
capacities, most researchers thought the difference must lie in the environments
surrounding the branches, which are very different. Pr
Contact: Susan McGreevey
Massachusetts General Hospital