RATS with severed spinal cords can sprint without re-growing the nerves between the injury and the brain, raising the prospect of a treatment for people with injured spines.
The key was to apply a combination of drugs and electrical impulses. 鈥淚t was incredible to look at,鈥� says neurobiologist Gr茅goire Courtine of the University of Zurich, Switzerland.
The spinal cord turns signals of intent from the brain into signals that propel muscles into motion. Damage to the spine can disrupt this signalling. But networks of neurons known as central pattern generators (CPGs), found in the spinal cords of rats and mice, can trigger movement without the help of the brain. They can be stimulated electrically or with chemicals that mimic various neurotransmitters. If humans also have CPGs, a similar combination of treatments might restore movement after spinal injuries.
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In past experiments, giving rats these treatments separately induced rhythmic hind-leg movements, but the animals couldn鈥檛 support their body weight. To see if combining the two treatments might do the trick, Courtine and his colleagues injected paralysed rats with drugs, including one that mimics the effect of the neurotransmitter serotonin and applied steady bursts of electricity to their spinal cords, via electrodes on the surface of the skin.
This enabled the animals to walk, sprint, step sideways and jog backwards, and crucially, after two months鈥� training, they could bear their own weight (Nature Neuroscience, ). It鈥檚 not clear why the treatments work so well in tandem, but Courtine suggests that the drugs somehow prime the CPGs for electrical activation. 鈥淐ombining the two created an exquisite synergy,鈥� he says. The trained rats could also respond swiftly to changes in pace and direction on the treadmill.
鈥淭he rats could walk, sprint, step sideways and jog backwards on the treadmill鈥�
His team are working on an wireless implant for people, which would be inserted into the spine below an injury, where it would deliver electrical pulses to target neurons. They would also need to find a way of regularly infusing serotonin mimics near these neurons, to avoid affecting the rest of the nervous system.
The rats didn鈥檛 recover their sense of balance, though, and needed the help of a robotic arm to run. People receiving the treatment in future might use a walking frame.
Mark Bacon, head of research at Spinal Research in Guildford, UK, says this is an important piece of research, but that it鈥檚 not clear whether it will work in humans.