Paralyzed Rats
Walk Again
By Jennifer Thomas
HealthDay Reporter by Jennifer Thomas
healthday Reporter – Sun Sep 20,
7:02 pm ET
SUNDAY, Sept. 20 (HealthDay News) -- A three-pronged approach to treating spinal cord
injuries allowed paralyzed rats to walk without receiving signals
from the brain, scientists report.
Spinal cord
injuries result in paralysis when the nerve fibers that carry
information to and from the brain are damaged or severed. Much of the focus of
research into spinal cord injuries has been exploring ways of regenerating
those nerve fibers and connections, which has so far met with limited success
in people.
In the new study,
rats were treated with a combination of drugs, electrical stimulation of
the spinal cord and locomotor training, a rehabilitation technique. The
combined treatment enabled the rats to walk with a near-normal gait on a
treadmill, without the muscles receiving signals from the brain.
"The study
demonstrates that the lower spinal cord has circuitry that is sufficient to
support virtually normal, weight-bearing locomotion," said senior study
author V. Reggie Edgerton, a professor of physiological sciences and
neurobiology at the
The study appears
in the Sept. 20 online edition of Nature Neuroscience.
Previous research
has been able to coax a stepping motion using one or two of those techniques,
said Susan Howley, executive vice president of research for the Christopher
& Dana
Reeve Foundation, which provided some funding for the current
research. But this is the first study to achieve actual weight-bearing walking,
as opposed to the motions of walking.
"The thing
that's very exciting about this is that for the first time they actually showed
they can get these rats, with no input from the brain, to step near
normally," Howley said. "On the treadmill, they were able to bear
weight and step virtually as well as they had been prior to the injury. That's
a remarkable achievement."
In the study,
researchers put rats whose lower legs were paralyzed in a harness on a
slow-moving treadmill and gave them a drug called quipazine, a serotonin
agonist that enhances the function of the spinal nerve circuitry. The researchers then
used an epidural to apply electrical currents to the dura of the spinal cord,
the protective membrane that surrounds it, below the point of injury.
The combination
of drugs and electrical
stimulation caused the rats to begin walking. Several weeks of
daily locomotor training on the treadmill enabled near-normal weight-bearing
walking -- including backward, sideways and running.
Because the brain
was still unable to direct the walking, the rats could only walk when hooked up
to electrical stimulation on the treadmill.
Previous studies
have shown that the nerve circuitry of the spinal cord is able to generate
rhythmic activity that can direct leg muscles to step, the researchers said.
With the right input, the nerves can learn to interpret sensory information
from the stepping motion even without help from the brain.
"Previous
research has shown the spinal cord can learn whatever task it's being trained
to do," Edgerton said. "The spinal cord can interpret the sensory
information associated with the stepping, respond to that sensory information
and sustain the stepping based on the sensory information."
Locomotive
training is a rehabilitation technique that uses that concept to retrain the spinal cord circuitry
after injury. Widely used in some European countries, locomotor training
involves placing people with spinal
cord injuries in harnesses while physical therapists move their legs in a
walking motion.
People who
undergo locomotor training often see improvements in respiration, bladder
function, blood sugar levels
and circulation below the level of the lesion, which can help prevent the skin
breakdown that can occur as a result of paralysis, Howley said. Others even
recover trunk stability, which can enable them to move from a bed to a
wheelchair, or a wheelchair to a car, without assistance.
Though a treatment
using the three-pronged approach is at least several years away, the study
suggests the potential of using neuroprosthetic devices to activate spinal cord
rhythmic circuitry, said study author Gregoire Courtine, a professor in the
department of neurology at the
About 5.6 million
Americans, or one in 50, has some level of paralysis,
according to a survey released in April of 33,000