Roger Highfield The Daily Telegraph - Roger Highfield describes experiments that pin down why some paralysed people stage a spontaneous recovery
Hundreds of thousands of people with spinal cord injury have been given hope that one day it might be possible to reroute the nervous system to restore walking and movement.
Spinal cord damage at the neck blocks the routes that the brain uses to send messages to control the legs. The body does have some ability to regenerate crushed or severed nerves but, until now, doctors believed that it was impossible to re-grow the long nerve highways that link the brain and base of the spinal cord.
For the first time, a study shows that the central nervous system can reorganise itself and follow a network of new, shorter, pathways around the damage to restore the cellular communication required for movement, a find that the team at the University of California, Los Angeles, led by Prof Michael Sofroniew believes has "important implications."
Published in the journal Nature Medicine, the discovery could pave the way to new therapies for those who suffer from traumatic spinal cord injuries and also explains why some patients do manage to recover to varying degrees.
"We think that it does happen naturally in some patients, as it did in our mice, and that this is one of the sources of 'spontaneous recovery'", Prof Sofroniew tells The Daily Telegraph.
"Imagine the long nerve fibres that run between the cells in the brain and lower spinal cord as major freeways," explains Prof Sofroniew. "When there's a traffic accident on the motorway, what do drivers do? They take shorter surface streets. These detours aren't as fast or direct, but still allow drivers to reach their destination.
"We saw something similar in our research," he adds. "When spinal cord damage blocked direct signals from the brain, under certain conditions the messages were able to make detours around the injury. The message would follow a series of shorter connections to deliver the brain's command to move the legs."
"The degree to which this rerouting of information happens varies, and this variation will depend on many factors, such as the severity of the tissue injury that can also damage these alternate nerve pathways.
"We also think that in some cases the alternate pathways may be there, but are not getting used properly. The next goal is to figure out how to maximise the use of these alternate pathways through a combination of training and stimulation. But there is still a lot more work to be done in this regard."
In the studies of mice, Prof Sofroniew and his colleagues blocked half of the long nerve fibres in different places and at different times on each side of the spinal cord. They left untouched the spinal cord's centre, which contains a connected series of shorter nerve pathways. The latter convey information over short distances up and down the spinal cord.
"We were excited to see that most of the mice regained the ability to control their legs within eight weeks," says Prof Sofroniew. "They walked more slowly and less confidently than before their injury, but still recovered mobility."
When the researchers blocked the short nerve pathways in the centre of the spinal cord, paralysis returned. This step confirmed that the nervous system had rerouted messages from the brain to the spinal cord via the shorter pathways, and that these nerve cells were critical to recovery.
"Our findings add to a growing body of research showing that the nervous system can reorganise after injury," he adds. "What we demonstrate here is that the body can use alternate nerve pathways to deliver instructions that control walking."
The team's next step will be to learn how to entice nerve cells in the spinal cord to grow and form new pathways that connect across or around the injury site, enabling the brain to direct these cells. If the researchers succeed, the findings could lead to the development of new strategies for restoring mobility following spinal cord injury.
"Our study has identified cells that we can target to try to restore communication between the brain and spinal cord," explains Prof Sofroniew. "If we can use existing nerve connections instead of attempting to rebuild the nervous system the way it existed before injury, our job of repairing spinal cord damage will become much easier." However, he stresses that more work must be done before human trials can be contemplated.
Prof Geoff Raisman of University College London comments that he had observed this phenomenon in experiments he had conducted in 1969 and that it is well known that some patients show spontaneous improvements, partly as a result of new bridging connections.
"There has been a surge of interest in the possibility that such connections could be induced by therapeutic interventions."