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© ALS Independence 2003-08
Nov 13th 2008
From The Economist print edition
A FEW years ago researchers found a way to create a remotely
controlled on-off switch in a neuron by inserting a light-sensitive gene into
the nerve cell. Now the same technique has been used experimentally in
laboratory rats in a study that could help with spinal-cord injuries.
When the spinal cord is severed instructions being sent from the brain are
interrupted. This means not just the loss of the ability to move limbs, but also
impairment of the up and down movement of the diaphragm too. This leaves
patients unable to breathe on their own and often causes death.
Jerry Silver, a neuroscientist at Case Western Reserve University in Cleveland,
Ohio, wanted to know if he could use light-sensitive genes to stimulate activity
in neurons that control the diaphragm. Dr Silver and his colleagues partly
severed the spinal cords of laboratory rats at the second vertebra. This is
where the neck swivels, and where many humans suffer spinal-cord injuries. It is
also where neurons that control breathing are located.
The partial injury (there are no ventilators for rats, so the researchers could
not completely sever the cord without killing them) allowed only one side of the
diaphragm to work and the rats had trouble breathing. A virus carrying genes for
a light-sensitive protein called Channelrhodopsin-2 was then injected into
neurons located just below the injury, at an area also involved with the
diaphragm.
Four days later, the animals’ spines were opened. The application of continuous
light on them had no effect. But as cells seem to respond most to patterns, the
researchers experimented with various pulses of light. Several hours after a
session which involved one-second pulses for five minutes followed by five
minutes of rest, the rats began breathing normally for a day and a half.
Tests confirmed that their blood was well oxygenated and, perhaps more
remarkably, that the two halves of their diaphragms were working in step with
each other. This, Dr Silver is convinced, is because the activity in the
light-sensitive neurons somehow activated a latent nerve pathway that spans both
sides of the spinal cord, allowing them to synchronise.
Dr Silver is hopeful that the work on rats, which is published in the Journal of
Neuroscience, will have relevance to humans—and not just those with spinal-cord
injuries. The technique could eventually help people suffering from amyotrophic
lateral sclerosis and multiple sclerosis. It might also lead to useful “off”
switches as well as “on” ones, which could allow certain conditions, such as
chronic pain, to be turned off.
How to get light to the neurons once they have been treated without cutting
people up is a problem that Dr Silver expects soon to be resolved. Methods are
already being developed to implant a light source inside the body which could be
activated by remote control. Another method would be to pipe the light in
through tiny cables. The fibre-optic age may be about to strike neurosurgery.
"Time is the coin of your life. It is the only coin you have, and only you can determine how it will be spent. Be careful lest you let other spend it for you." Carl Sandberg
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© ALS Independence 2003-08