Tiny nerves crisscrossing the spine can bypass crippling
injuries recently written off as irreversible, scientists reported
in a study published Monday.
Experiments conducted on mice at the University of California in
Los Angeles showed for the first time that the central nervous
system can rewire itself to create small neural pathways between
the brain and the nerve cells that control movement.
This startling discovery could one day open the way to new
therapies for damaged spinal cords and perhaps address conditions
stemming from stroke and multiple sclerosis, according to the
study.
Normally, the brain relays messages that control walking or
running via neural fibers called axons.
When these long nerves are crushed or severed -- in a road crash
or sports accident, for example -- these lines of communication are
cut, resulting in reduced movement or paralysis.
"Not long ago, it was assumed that the brain was hard-wired at
birth and that there was no capacity to adapt to damage," explained
neurobiologist Michael Sofroniew, who led the research.
But the new findings add to a growing evidence of the brain's
remarkable capacity to reorganise in response to injury "in ways
that were not thought possible," he told AFP.
Sofroniew compared the axons to major freeways running from the
brain to the lower spinal cord.
"When there is a traffic accident on the freeway, what do
drivers do? They take shorter surface streets," he said.
In the same way, the short nerves found up and down the spinal
cord, called propriospinal connections, set up alternate
routes.
"These detours aren't as fast or direct, but still allow drivers
to reach their destinations," he said, completing the metaphor.
In the experiments, Sofroniew and his colleagues blocked half of
the long axon nerve fibers in mice in different places, and at
different times, on either side of the spinal cord, paralysing the
animals' hind legs.
They left untouched the spinal cord's core, which contains the
shorter nerves.
Astonishingly, most of the mice regained control of their legs
within eight weeks, albeit with less mobility than before.
When the researchers blocked then shorter propriospinal nerves,
the mice were once again paralysed, proving that they had been
responsible for the recovered mobility.
The challenge for medicine will be finding ways to enhance and
harness this spontaneous neural rewiring to help heal spinal cord
injuries.
Up to now, most experts believed that the only way for injured
patients to walk again was to regrow the long axon, but it has been
extremely difficult to get these damaged "highways" to regenerate
more than a short distance.
"The next goal is to determine how to maximise the process
through the right kind of rehabilitation and training, and to test
whether there are any forms of pharmacologic stimulation that might
help as well," said Sofroniew.
More than a quarter of million people in the United States
suffer from spinal cord injury, with some 10,000 new cases every
year, according to epidemiological studies. Worldwide, the rate of
new cases is between 15 and 40 cases per million every year.
(Agencies via China Daily January 8, 2008)