Health - Rapid nerve repair helps lame rats walk within days

A simple, cheap procedure for repairing damaged nerves in the leg can help paralysed rats walk normally within a few days – a dramatic reduction in recovery time.

Within minutes of the rats waking up after the operation, they began to move their damaged limb, and 98 per cent of them had recovered 60 to 70 per cent of leg function within two to four weeks. Conventional treatments would never give the rats such a level of recovery.

After a nerve is severed it is important to reconnect the two ends as quickly as possible, because the disconnected section withers away after a few days of isolation. The usual technique is to stitch the loose ends together – but the body's own repair system can stand in the way of a successful mend.

Earlier studies by George Bittner of the University of Texas at Austin and his team revealed where the fault lies: it's with the tiny spheres called vesicles that the body creates in the nerve stumps.

"Normally, the vesicles would repair each of the two cut ends," says Bittner. But if they do so before the two ends can be brought back into contact, the vesicles simply seal the two stumps off, making it difficult to create a connection between them later on.

Calcium-free zone

If calcium is excluded from the injury site, though, the vesicles don't form and the body's self-repair process is aborted. This leaves the damaged nerve ends unsealed and in a better state for surgical reattachment.

So in the first step of Bittner's new procedure, he injects the injury site with a calcium-free salty solution to prevent the self-repair mechanism from kicking in. "It becomes a calcium-free zone," he says.

In step two, he pulls the two jagged nerve ends to within a micrometre of each other and squirts a polymer called polyethylene glycol (PEG) between them. It removes water from the outer, fatty membrane of each nerve stump, allowing the fats in the membranes to merge together again and reconnect the two nerve ends – the starting point for proper healing.

In the final step, Bittner restarts the natural healing process by immersing the injury site in a calcium-rich salty solution. That triggers the body to begin producing vesicles. Because the two nerve ends are now reconnected, the vesicles create a strong seal around the join.

Messy reality

Bittner has successfully deployed the procedure in 200 trials in rats on peripheral nerves such as the sciatic nerve.

"As a beginning, it's very encouraging," says Giorgio Terenghi, head of nerve regeneration research at the University of Manchester. "The important thing is that the PEG keeps the contact between the severed ends," he says.

Terenghi says the real challenge will come in dealing with the extensive and messy injuries that turn up in emergency rooms, where the two severed ends might end up too far apart to be reunited.

Journal references: Journal of Neuroscience Research, DOI: 10.1002/jnr.23022 and 10.1002/jnr.23023

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