Scientists have been able to show that by treating spinal cord injuries in rats with a specific protein already found in the body, they can encourage sensory neurons to regrow and function over large distances. The new study is published in the Proceedings of the National Academy of Sciences.

By simulating crushed spines in lab rats, scientists at Tufts University School of Medicine have been able to show that by treating the breakage with a specific protein already produced by the body, called artemin, they can encourage the damaged nerve fibers to grow an incredible 4 centimeters (1.5 inches). Not only that, after four weeks of treatment, the regenerated neurons were fully capable of passing signals along the whole length.

This news blows out of the water any previous records of nerve fiber regrowth by a factor of ten. “This is a significantly longer length of Central Nervous System regeneration than has been reported earlier,” Eric Frank, one of the authors of the study, told Science Alert. “But [there’s] still a long way to go!”

Encouraging neurons to grow is notoriously difficult. As we get older, the body's ability to heal nerve cells decreases, and it also produces chemicals that for some reason prevent regeneration. The researchers at Tufts have been experimenting with the protein artemin—already known to be involved in the survival and development of neurons.

But if you thought that the length of growth was incredible, the news doesn't stop there. Not only have they managed to achieve unprecedented growth from the nerve fibers, but they’ve also gotten them to ‘plug’ themselves back into their original places. So whilst older studies found that when the sensory nerves were regenerated they would often get muddled up and cross each other, when the researchers used artemin, the new nerves were able to find their way back to the right spot and connect up correctly.

This suggests that there is some form of chemical guidance telling the neuron where to go that remains in the nerve fibers even into adulthood. If this is the case with sensory neurons, then it’s also probably true with other types of neurons. “If it becomes possible to get these other types of nerve fibres to regenerate for long distances as well, there is a reasonable chance that they can also grow back to their original target areas,” Frank explained.

If they can now get other types of nerve cells—such as motor neurons—to regenerate and reconnect in the same way they’ve managed with these sensory neurons, then we’d be moving a huge step forward in reversing paralysis.