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WASHINGTON, DC -- April 1, 1999 -- Scientists have found success in animals
with a promising new way to rejoin severed nerves quickly.
"The technique rejoins the cut or crushed ends of severed central and
peripheral nerve cells so that the repaired cells again conduct electrical
signals through the severed area within seconds to minutes after they are
rejoined," said George Bittner, Ph.D., of the University of Texas at Austin.
The central nervous system (CNS) includes the brain and spinal cord. The
peripheral nervous system (PNS) includes nerves found in the rest of the
body.
Several hundred thousand central and peripheral nervous system injuries
occur annually in the United States, primarily due to trauma and stroke.
There is currently no technique in humans or other mammals which can repair
severed nerves in the brain or spinal cord or speed up the repair of severed
peripheral nerves.
"The technique opens up a completely novel approach to restoring
physiological continuity in the injured nervous system," explained Michael
Selzer, M.D., Ph.D., a neurologist at the University of Pennsylvania.
Bittner's study is published in today's issue of The Journal of
Neuroscience.
Nerve cells possess axons, extensions that transmit electrical signals over
long distances in the body. When these biological transmission lines are
cut, their electrical signals can no longer be transmitted. Nerve cells in
mammals, including humans, usually cannot regenerate axons that are severed
in the CNS. At present, the functions once controlled by those axons cannot
be restored. Severed PNS axons regenerate very slowly, about one millimetre
per day.
In the new study, Bittner and his colleagues applied a calcium-free solution
of polyethylene glycol (PEG) for one to two minutes to the cut ends of
severed axons. PEG causes the cell membranes of closely approximated cells
to fuse. The researchers then washed off the PEG solution and bathed the
site where the axons had been joined in calcium solutions that mimic the
salt composition of mammalian body fluids. They found that within two to 30
minutes many of the once-severed axons regained their ability to transmit
electrical impulses through the lesion site. They then applied a biological
adhesive (a PEG-hydrogel) developed by one of the authors, Jeffery Hubbell,
Ph.D., who is now at the Swiss Federal Institute in Zurich, Switzerland.
This substance binds very tightly to the severed axons and prevents the
rejoined axons from pulling apart once the animal recovers from anesthesia.
The researchers have now successfully used this technique to rejoin the
severed halves of CNS and PNS axons from crayfish, earthworms, rats,
rabbits, and guinea pigs.
"This new approach can almost certainly be used to rapidly rejoin cut or
crushed axons in humans," Bittner said.
To aid this effort, Bittner and his colleagues have already published papers
showing how the severed ends of mammalian axons can be kept alive for at
least days after they are disconnected from their parent cells. An ability
to keep severed axons alive would give surgeons a longer time to rejoin
those axons with PEG solutions.
Selzer said that, until now, demonstrations that fused mammalian nerve
fibres can conduct electrical impulses have been performed in tissue
isolated from the body. Among crucial questions that remain are whether the
technique can fuse axons in a living mammal and whether this approach can
result in recovery of useful function.