In their experiments, the researchers first coaxed embryonic stem cells from mice to begin their transformation into motor neurons. Once these "pre-motor neurons" were implanted into the spinal cords of paralyzed rats, a constant drip of molecules that block the nerve-repelling activity of the spinal cord's myelin sheath gave the cells a chance to break through.
About 80 of an initial 12,000 neurons-in-training implanted into each rat became full-fledged motor neurons and pushed their finger-like extensions, called axons, through the spinal cord, the researchers reported April 26 in the Advance Online section of the Proceedings of the National Academy of Sciences.
"We think that getting new motor neurons to travel properly through the cord is the major hurdle to try to restore muscle control," says Douglas Kerr, M.D., Ph.D., an assistant professor of neurology. "It's significant that axons from these motor neurons make it outside of the cord."
However, he cautions that much remains before stem cells or cells derived from them could be useful for restoring lost or "broken" neurons in people. For example, in their experiments, even though some of the new neurons reached through the myelin coating, they didn't get much farther down the road to the real target -- muscles.
Furthermore, to approach therapy, Kerr says, these and other experiments need to be done with human embryonic stem (ES) cells that may one day be clinically useful. However, the human ES cell lines approved for research under federal grants -- by far the largest source of funding for academic researchers -- have been grown in the presence of mouse cells, which many scientists bel
Contact: Joanna Downer
Johns Hopkins Medical Institutions