Researchers have induced severed spinal nerves to regrow in rats, demonstrating for the first time, they say, that cells in mammals' central nervous systems contain the machinery to overcome barriers to regeneration.
Up to now, scientists have achieved minimal spinal cord regrowth in animals by tweaking the chemical environment of the damaged spine, or by transplanting fetal cells or peripheral nerves as a bridge for spinal nerves, which do not normally heal.The new research, published in the current journal Neuron, indicates that spinal nerves have the intrinsic capacity to regrow if a normally dormant genetic growth program is switched on.
"This finding represents a breakthrough in the sense that we can now say that regrowth occurs without putting either peripheral nerve grafts or embryonic tissue at site of injury," said Dr. Clifford J. Woolf of the Massachusetts General Hospital in Boston, who did the research with Simona Neumann. "We haven't changed the hostile environment. But we can get spinal nerve growth right through it."
Woolf said previous spinal regeneration experiments produced only "very limited" growth, but in the MGH study "a substantial number of nerve fibers regrew." However, the researchers have not yet shown that sensory function was restored -- a key issue.
Others in the field said the MGH research is an encouraging step toward a treatment that might help some of the 10,000 or more Americans who suffer devastating spinal cord injury each year. Its importance, they said, lies in directing attention on spinal neurons' machinery for regrowth.
"This raises some exciting questions," said Dr. Evan Snyder of Children's Hospital in Boston. "What are the factors that these cells are producing that makes them grow into the central nervous system, and grow further than you'd expect? It reinforces what many of us have always felt: that when you have spinal cord injury, it's not necessarily the end of the story."
"This work is significant in that it helps us focus on neurons' intrinsic capacity for regeneration," added Mary Ellen Cheung of the National Institute of Neurological Diseases and Stroke in Bethesda, Md. "If you turn on the appropriate molecular machinery, you get regeneration."
Injured nerve cells outside the brain and spinal cord do regenerate, but those in the central nervous system are programmed not to grow. Thus, cord injury can cause permanent paralysis and loss of sensation.
Most recent research in spinal cord regeneration has focused on overcoming the formidable obstacles to regrowth -- inflammation and scar tissue at the injury site, and growth-inhibiting chemicals that bathe central nervous system cells.