A team of scientists said they had “reawakened” a severed spine by stimulating spinal nerves using electrical currents from implanted electrodes, drug injections and exercise training.
It is the first study demonstrating that a severely damaged spinal cord can adapt and recover sufficiently to allow the brain to regain limb control.
The rats in the experiment were fitted with special robotic harnesses so only their hind legs reached the ground. They were then placed on a treadmill which produced only reflex stepping, and on ground where they had to choose to make their legs move if they wanted to reach a piece of chocolate as a reward.
They took their first voluntary steps after about two to three weeks of training, the researchers said but they still needed the harness to keep their balance.
Professor Grégoire Courtine, who led the five-year study at the University of Zurich and the technical university EPFL in Lausanne, Switzerland, said: “Our rats have become athletes when just weeks before they were completely paralysed.
“I am talking about 100 per cent recuperation of voluntary movement.”
Prof Courtine said plans were being made to begin clinical trials on humans in a bid to find a way to help people with spinal injuries that result in paralysis.
There are an estimated 40,000 people in the UK with spinal injuries. Among those in the 16-35 age group, most spinal injuries are caused by accidents. Describing the study, published in the June issue of the journal Science, Prof Courtine said: “After a couple of weeks of neuro-rehabilitation with a combination of a robotic harness and electrical-chemical stimulation, our rats are not only voluntarily initiating a walking gait, but they are soon sprinting, climbing up stairs and avoiding obstacles.”
It was known that the brain and spinal cord can adapt and recover from moderate injury, a quality known as neuroplasticity. But until now the spinal cord demonstrated so little “plasticity” after severe injury that recovery was considered impossible, the journal reported.
Prof Courtine found plasticity and recovery can take place in severe cases – but only if the dormant spinal column is first “woken up”. To do this, researchers injected a chemical solution of “monoamine agonists” into the rats – chemicals which bind to dopamine, adrenaline, and serotonin receptors on the spinal neurons.
These chemicals replace neuro-transmitters released by brainstem pathways in healthy subjects and excites neurons, making them ready to co-ordinate lower body movement when the time is right.
After the injection, scientists electrically stimulated the spinal cord with electrodes, readying the neurons and fibres for movement.
To provoke movement the team relied on a previous study by Prof Courtine, which had found a rat spinal column isolated from the brain could start to “walk” provided it was given the sensation of walking from a treadmill.
Dr Mark Bacon, director of research for the charity Spinal Research, said: “This is an elegant piece of work by a respected team. But in the real world the concepts might not be so amazing. However, the concepts are invasive but feasible so could be transferred to clinics pretty rapidly. But so much would depend on the severity of the injury and where it was on the spinal cord.”