A combination of drugs, electrical stimulation and regular exercise seems to help paralyzed rats walk, and even run, again, new research has found.
The findings suggest that the regeneration of severed nerve fibers is not required for paraplegic rats to learn to walk again and might help direct new treatment plans for people with spinal cord injuries.
Mmuch of the work on spinal cord injuries has been directed in recent years to using
stem cells to repair damaged spinal nerves and reconnect the spinal system with the brain. But this approach has so far met with limited success in people.
This new research focused on retraining the existing sensory system below the level of the injury in the spine.
A team led by Reggie Edgerton, a professor of neurobiology and physiological sciences at the David Geffen School of Medicine at UCLA tested rats with complete spinal injuries that had no voluntary movement in their hind legs.
After placing the paralyzed rats in a harness and setting them on a moving treadmill, the scientists administered a drug called quipazine that acts on the neurotransmitter serotonin. They then used an epidural to apply low levels of electrical currents to the spinal cord below the point of injury.
The researchers think that the sensation derived from the rats' legs moving on a treadmill, combined with the drugs and neurostimulation triggered the spine's rhythm-generating circuitry and prompted the rats' paralyzed hind legs to begin stepping.
Not only did the rats begin to walk with no input from the brain, but purely from the reflexive action of their sensory system, after daily treadmill training over several weeks, they were soon also able to support their body weight, an important achievement, say the researchers.
"The spinal cord contains nerve circuits that can generate rhythmic activity without input from the brain to drive the hind leg muscles in a way that resembles walking called 'stepping,'" explained Edgerton.
"Previous studies have tried to tap into this circuitry to help victims of spinal cord injury," he added. "While other researchers have elicited similar leg movements in people with complete spinal injuries, they have not achieved full weight-bearing and sustained stepping as we have in our study."
But once the drugs and electrical stimulation were stopped, the rats were unable to walk on their own.
Still, the researchers say there are "neuro-prosthetic devices" that may bridge human spinal cord injuries to some extent, so activating the spinal cord rhythmic circuitry as the UCLA team did may help in rehabilitation after spinal cord injuries.
The study was funded by the Christopher and Dana Reeve Foundation, among a number of other international spinal research groups. The results are published in the online edition of Nature Neuroscience.
