Mice walk again after spinal cord injuries

Published: January 7, 2008  |  Source: news.com.au
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SCIENTISTS have figured out how mice can regain some ability to walk after spinal cord injuries, and hope this insight can lead to a new approach to restoring function in people paralysed by similar damage.

The research, published today in the journal Nature Medicine, showed the brain and spinal cord were able to reorganise functions after a spinal cord injury to restore communication at the cellular level needed for walking.

Mice given partial spinal cord injuries in the laboratory were gradually able over a period of about eight to 10 weeks to regain the ability to walk, although not as well as before the injury, according to the scientists.

After this partial spinal cord injury, the brain and spinal cord underwent a sort of spontaneous rewiring to control walking even in the absence of the long, direct nerve highways that normally connect the brain to the walking centre in the lower spinal cord, the researchers said.

“This is not the end of a story. This is the beginning of a story,” said Dr Michael Sofroniew, a professor of neurobiology at the David Geffen School of Medicine at the University of California at Los Angeles who led the research.

“We have identified what appears to be a previously unrecognised mechanism for recovery of function after these kinds of injuries. And we need to understand it better and learn how to exploit it better, through doing the right kind of rehab training and through figuring out ways to stimulate this kind of recovery,” Dr Sofroniew said.

The spinal cord passes through the neck and back and contains nerves that transport messages between the brain and the rest of the body.

A spinal cord injury – from a car accident, for example – can cause paralysis below the site of the injury. There is no cure for such paralysis, and many scientists have been frustrated by their failure to find one.

Spinal cord damage obstructs the pathways the brain uses to transit messages to the nerve cells that control walking.

Experts had thought the only way someone with such an injury could walk again was to somehow regrow the long nerve highways linking the brain and base of the spinal cord.

But what they found in this study was that when spinal cord damage blocked direct signals from the brain, the messages were able to make detours around the injury.

Rather than using the long nerve highways, the message would be transmitted over a series of shorter connections to deliver the brain’s command to move the legs, the researchers said.

Dr Sofroniew used a traffic analogy. “If you have a big freeway going somewhere, then that’s the fastest route to take. If that gets blocked and you can’t get through, an alternative way might be simply to get off the freeway and use shorter interconnected side streets to get around.”

The researchers blocked half the long nerve fibres on each side of the spinal cord but did not disturb its centre, which has a connected series of shorter nerve pathways that convey information over short distances up and down the spinal cord.

The researchers then blocked the short nerve pathways in the centre of the spinal cord, which caused paralysis to return. This confirmed the nervous system had rerouted messages from the brain to the spinal cord using these shorter pathways.

The researchers said they now hoped to figure out how to encourage nerve cells in the spinal cord to grow and form new pathways that connect across or around an injury, permitting the brain to direct these cells and avert paralysis.

By Will Dunham in Washington