A complex combination of drugs, electrical stimulation and regular exercise can enable paralyzed rats to walk and even run on a treadmill. The study published online this week in Nature Neuroscience suggests that regeneration of severed nerve fibers is not required for paraplegic rats to learn to walk again. This finding may have implications for rehabilitation after spinal cord injuries

The spinal cord contains nerve circuits that can by themselves, without input from the brain, generate rhythmic activity to drive leg muscles in a way that resembles walking. Numerous studies have attempted to tap into this circuitry to help victims of spinal cord injury, but while leg motion can indeed be elicited, no weight-bearing walking has yet been achieved.

Gregoire Courtine and colleagues subjected rats to a complete spinal injury, such that they had no voluntary movement in their hind limbs. They set these paralyzed rats on a slowly moving treadmill while administering certain drugs as well as applying specific electrical currents to the spinal cord below the point of injury. This triggered the spinal rhythm-generating circuitry and elicited walking motion in the paralyzed hind limbs. Daily treadmill training over several weeks enabled full weight bearing walking, even backwards, sideways, and running.

The rats' injury still left the connection between the brain and the spinal cord-based rhythmic walking circuitry interrupted. The rats were therefore unable to walk of their own accord. In human patients, since neuroprosthetic devices may in principle bridge spinal cord injuries to some extent, activating the spinal cord rhythmic circuitry as this study has may help in rehabilitation after spinal cord injuries.