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Why is finding a cure so difficult?
Repairing a damaged spinal cord is an extrememly complex challenge, but one where there have been huge advances in the past 15 years.
Not only are many spinal neurons killed by the initial injury, but in the days and weeks following the accident more neurons are killed by the body's own response to the injury.
This is a considerable challenge
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Then - the body lays down an impenetrable scar tissue at the site of the injury which acts as a formidable barrier to any neurons that might be trying to grow. Finally, any neurons which have escaped death may lose their insulating myelin sheath so can’t function and pass messages.
To repair spinal cord injuries, scientists would not only have to solve all the problems above, but would then need to find ways of making the neurons grow to exactly the right part of the spinal cord, and form synapses with exactly the right neurons. |
Keeping neurons alive
Any treatment for spinal cord injury will need to address many of these separate challenges, the first of which is keeping the surviving neurons alive.
Most spinal injuries do not sever the whole spinal cord, so some neurons remain alive. However, the body begins to kill neurons close to the injury site (secondary damage). Scientists are looking at ways of preventing this secondary damage by stopping the dying cells sending out signals, and by altering the immune response.
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During the development of the nervous system, some cells serve their purpose for a short time and are then programmed to commit suicide (apoptosis). Scientists think this programmed cell death might be re-activated after a spinal cord injury so are looking at ways to stop it.
Making neurons grow
One way of stimulating nerves to grow is to add growth factors. The tricky part is how to deliver these factors to the injury site without causing further damage to the sensitive spinal cord. One option has been to genetically engineer cells to produce large amounts of growth factors and to inject these cells.
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Getting through the impenetrable glial scar
At the site of injury, a scar tissue forms which pumps out molecules that stop neurons growing. After years of painstaking work, scientists have identified many of these molecules.
Proteoglycans seem to be particularly important and 5 years ago, scientists found ways of degrading some of these proteoglycans in tissue culture allowing neurons to grow further. |
Two years later scientists were able to use the same treatment in rats with spinal cord injury and show they could recover some of the lost function in their limbs.
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Amazing advances with cells for smell
Recently, scientists have made amazing advances in repairing spinal cord injuries in rats by injecting olfactory ensheathing cells.
These cells are remarkable, in that they normally surround olfactory neurons, one of the very few types of brain neuron that can regenerate.
Somehow, the olfactory ensheathing cells provide an environment that promotes axon growth.
Geoff Raisman and his group in London have found ways of injecting these olfactory ensheathing cells into the spinal cord.
The results have been astounding and human trials will begin soon in collaboration with The Royal National Orthopaedic Hospital, Stanmore. |
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The amazing thing about these olfactory ensheathing cells is what happens when they come in contact with the normally barrier-like astrocytes of the glial scar. ‘It’s almost like they knock on the door and the astrocytes open up’ said Geoff Raisman.
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Stem cells
A recent paper (2005) from Hans Kierstead in California has showed that human embryonic stem cells injected into the spinal cord also improves mobility in rats with recent spinal cord injuries. |
The way forward…
In 2005, a collaboration of scientists from around the world used a combination of several approaches. They were able to show significant recovery of limb function and regeneration of axons following spinal cord injury.
They used:
- An enzyme to break down the inhibitory proteoglycans in the glial scar
- Schwann cells (from the peripheral nervous system) to encourage nerves to grow.
- Olfactory ensheathing cells to ensure the axons could grow out of the graft and back into the spinal cord.
More about this study
Find out what each of your spinal nerves does, and the effects of damaging them.
For the very latest in research, visit the Spinal Research website
For information and advice, visit the Spinal injuries Association website
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