Image: Courtesy of DAVID ANDERSON California Institute of Technology

Stem cells injected into the spinal fluid of newly paralyzed mice and rats can restore movement, according to a study described yesterday in New Orleans at the annual meeting of the Society for Neuroscience. Unlike most stem cell research, which has focused on repairing damage to small areas of the central nervous system (such as injuries caused by a stroke), this study is among the first to demonstrate the efficacy of stem cell treatment in restoring function over a large region of the central nervous system. Researchers say the new findings may lead to better treatments for human patients afflicted with motor neuron diseases such as amyotrophic lateral sclerosis (ALS) and spinal motor atrophy (SMA), which ultimately lead to paralysis and death.

Investigators led by neurologist Douglas Kerr of Johns Hopkins University injected neural stem cells (like those shown in the photograph) into the cerebrospinal fluid of 18 rodents infected with the Sindbis virus, which normally leads to permanent paralysis. Several weeks later the cells had migrated from the injection site at the based of the spinal cord up to the so-called ventral horn, a region that contains the bodies of motor nerve cells. "After eight weeks we saw definite functional improvement in half of the mice and rats," Kerr reports. "From 5 to 7 percent of the stem cells that migrated to the spinal cord appeared to differentiate into nerve cells."

Exactly how so few nerve cells can confer this considerable improvement in function is a question the team is working to explain. "It could be that fewer nerve cells are needed for function than we suspect," Kerr surmises. "The other explanation is that the stem cells themselves havent restored the nerve-cell-to-muscle units required for movement but that, instead, they protect or stimulate the few undamaged nerve cells that still remain." Whatever the answer, the results do offer hope. "Under the best research circumstances," says team member Jeffrey Rothstein, "stem cells could be used in early clinical trials within two years."