Scientists have found a chemical which can influences the direction of nerve cell growth - and say it could help repair damaged spinal cords.
Scientists used the chemical in laboratory tests
One of the reasons that severe spinal cord injury causes permanent damage is that the nerve cells involved do not regrow in the same way as normal cells.
Scientists are hopeful that there must be naturally-produced chemicals which encourage these "axons" to grow out and bridge the gaps caused by injury or disease.
However, these chemicals have remained elusive.
Now a team of scientists from Johns Hopkins University in Baltimore, US, has found, by chance, a chemical which appears to be able to influence nerve growth.
When they put cells next to a source of the substance, called semaphorin-7a, there was more cell growth in the direction of the source than in other directions.
Mice bred to lack semaphorin-7a had brains which did not develop properly.
The scientists believe that if they can harness this chemical, and others like it which have the opposite effect, it might one day be possible to encourage spinal injuries to heal more efficiently.
Professor Alex Kolodkin, one of the researchers, said the find was impressive but that much work remained to be done.
"I've been studying semaphorins for about a decade and didn't expect to find any that stimulated axon growth, certainly not to extent we saw in the lab and in mice.
"Now we need to figure out how semaphorins balance their repulsive and attractive effects."
He said that it might be problematic to encourage growth in one type of cells - nerve cells - without getting unwanted growth elsewhere.
His colleague Dr Jeroen Pasterkamp, who co-authored the research, published in the journal Nature, said: "Our next steps are to find otu exactly how semaphorin-7a's message is passed along inside the nerve, which will hopefully reveal a useful, specific target for promoting axon growth following nerve injury or degeneration."
Dr Patrick Mehlen, from the University of Lyon in France, said: "A deeper understanding of the intracellular signalling pathways that are activated by semaphorins will provide insight into a variety of physiological processes, from vascular and neural development to immunity."