Monday, May 03, 2004

Stem Cell Spinal Nerves Break Through

Exiting of spinal cord a step to their use for treating paralysis
By Gabe Romain, Betterhumans Staff

Stem cell-derived nerves have been prompted to migrate through the spinal cord in mice, an important step to their use for treating spinal cord damage in humans.

In experiments with rodents, researchers at The Johns Hopkins School of Medicine in Baltimore, Maryland overcame a big hurdle to restoring function in severely damaged central nervous systems: Getting new motor neurons to migrate through the spinal cord.

"We think that getting new motor neurons to travel properly through the cord is the major hurdle to try to restore muscle control," says John Hopkins researcher Douglas Kerr. "It's significant that axons from these motor neurons make it outside of the cord."

Blocked signals

The spinal cord carries sensory and motor signals to most of the skeletal muscles in the body. Just about every voluntary muscle in the body below the head depends on the spinal cord for control.

Paralysis can occur when a traumatic event damages cells in the spinal cord or severs the nerve tracts that relay signals up and down the spinal cord.

While rehabilitative treatments help many people with spinal cord injury, methods for reducing the extent of injury and for restoring function are limited.

One strategy to repair damaged spinal cords involves directing stem cells into areas where neurons are damaged.

Much work remains, however, before researchers can use stem cells or cells derived from them to restore lost or damaged neurons in people.

A bit part of the problem is that stem-cell derived nerves are blocked from reaching muscles by myelin, which forms a sheath that insulates nerves and also inhibits the growth of axons, the nervous system's primary transmission lines.

Moving towards muscle

For their study, Kerr and colleagues first coaxed embryonic stem cells from mice to begin their transformation into motor neurons?also known as motoneurons.

They then implanted the motoneurons into paralyzed rats. "We transplanted roughly 12,000 cells per animal, and about 4,000 of them 'took,'" says Kerr. "They became true motor neurons and looked gorgeous."

Initially, the neurons didn't poke through the spinal cord and out into muscles because of the spinal cord's myelin sheath.

So the researchers used a constant drip of molecules that block the nerve-repelling activity of myelin to allow the cells to break through, and some did.

While the study is promising, however, the researchers say that much more work is needed because while the neurons were coaxed through the myelin sheath they didn't get much farther down the road to the real target: Muscles.

The research is reported in the Proceedings of the National Academy of Sciences.