When treated with the right proteins, severed nerves will sink new roots into the spinal cord. In experiments described in today's Nature, rats regained their senses of heat and pressure in their injured paws, suggesting that the therapeutic proteins helped neurons recover the right connections.
A fingertip sewn back onto a hand will often regain feeling as nerves heal. But reconnecting sensory nerves to the spinal cord has proved difficult because the spinal cord beats back neurons that try to patch into it. Neuroscientist Matt Ramer and his co-workers at King's College and Queen Mary and Westfield College, both of the University of London, wondered whether doses of neurotrophic factors--proteins that help developing neurons grow, and mature ones stay healthy--might overcome the spinal cord's antipathy to healing neurons. "What we're trying to do," says Ramer, "is give the neurons a regenerative boost."
To give this a try, Ramer's team first crushed the threadlike nerves that connect the forelimbs to the spinal cord in rats. In some animals, the researchers injected neurotrophic factors near the damaged nerves. After 7 days, the researchers examined the healed nerves under a microscope and found regenerated neurons reaching into the cord. In the rats that did not receive the factors, neurons stopped at the cord's outer layer. Only in the treated rats did the reconnected nerves work: Electrical pulses applied to nerves in the paw zipped through to the spinal cord. And only the treated rats withdrew their paws when squeezed or heated.
The findings show that healing neurons can make the right connections to deliver meaningful signals to the brain, says John Steeves, a neuroscientist at the University of British Columbia, in Vancouver. "What's nice about this," he says, "is that it shows not only regeneration, but also functional recovery."