With the help of a robotic harness, some drugs and electrodes, rats with severed spinal cords are sprinting and climbing up stairs! Someday, a similar method of neurorehabilitation could help restore leg movement in paralyzed humans.
Nerve fibers that help move muscles in the body don’t regrow in adults. In spite of the nervous system’s amazing capacity to forge new connections around an injury, nerve damage to a severed spinal cord is generally considered too great for repair.
To challenge this view, a Swiss team led by Grégoire Courtine of Swiss Federal Institute of Technology (EPFL) studied rats with injuries similar to those causing lower-body paralysis in people.
"This is the world-cup of neurorehabilitation," Courtine says in a release. "Our rats have become athletes when just weeks before they were completely paralyzed. I am talking about 100% recuperation of voluntary movement."
- First, they excited dormant neurons in the rats by injecting neuro-activating chemicals. These chemicals bind to dopamine, adrenaline, and serotonin receptors – creating a cocktail that replaces neurotransmitters released by brainstem pathways in healthy subjects.
- Then they used electrical stimulation with electrodes implanted in the spinal cord. This sends continuous electrical signals through nerve fibers to the chemically excited neurons.
- Together, these steps reactivated the neurons controlling the rats’ hind limbs and primed them to make new connections.
- They outfitted the rats with little vests attached to a robotic system. The robot-assisted harnesses didn’t propel them, but just supported them up on their hind legs so they could walk forward without falling.
- Over a couple weeks, one group of rats learned to walk across solid ground, crossing a platform to reach their chocolate reward. With more rehab, they even managed to sprint up rat-sized stairs and step over low obstacles to get to their treat. These rats regained voluntary control, walking and bearing their full weight on their hind legs. Watch the video!
- Another group of rats didn’t underdo this rehab, and were trained using a treadmill. They automatically moved their legs as the treadmill moved below their feet – BUT, they lacked the active decision-making of the first group of rats. Walking essentially occurred without any input from the rat's actual brain, so they didn’t manage to walk voluntarily on solid ground.
The rehab remodeled the circuitry all the way from the spinal cord up through the brain. But the experiment with the treadmill-trained rats suggests that full recovery depends on making intentional movements, not just any movement, ScienceNOW explains.
The rats had to engaged, participating in their own rehabilitation. "In the beginning... the animal is struggling and it is really difficult," Courtine tells AFP. "Then the first time it happens, the animal is surprised. It looks at you like, 'Wow. I walked!'"
“Willpower-based training translated into a fourfold increase in nerve fibers throughout the brain and spine,” explains study researcher Janine Heutschi of EPFL. Courtine thinks this regrowth is like a duplication of an baby’s growth phase. The newly formed fibers bypassed the original spinal lesion and allowed signals from the brain to reach the electrochemically-awakened spine.
Human, phase II trials might begin in a couple years Switzerland. EPFL researchers are coordinating an $11.1 million project called NeuWalk, which aims to design a fully operative spinal neuroprosthetic system for implanting into humans.
The findings were published in Science yesterday.