In 2000, Johns Hopkins scientists reported that neural stem cells had helped restore movement in paralyzed rodents. The study involved 18 mice and rats whose motor neurons had been damaged by Sindbis virus, an infection that causes paralysis in these animal models. Researchers introduced neural stem cells into the animals’ cerebrospinal fluid and observed that the transplanted cells migrated toward damaged regions of the spinal cord. After several weeks, about half of the treated rodents demonstrated functional improvement, including the ability to place one or both hind feet on the ground. The findings provided an early indication that stem cells might someday contribute to repairing damaged parts of the nervous system.
What made the 2000 research particularly interesting was the way the stem cells responded to damage. Instead of remaining where they were introduced, some of the transplanted cells moved toward areas of injury within the spinal cord. The researchers found that approximately 5 per cent to 7 per cent of the stem cells that reached the spinal cord appeared to differentiate into nerve cells. Scientists were still investigating whether the new cells directly restored nerve-to-muscle connections or whether the transplanted cells protected or stimulated surviving neurons. That uncertainty was important because the study demonstrated a functional effect without fully explaining the biological mechanism behind it.
