Motor neurons rely on astrocytes—like the one shown here in green—for nutrition, protection, insulation, and support. When astrocytes are defective, they can turn against the neurons they're meant to protect.

Scientists are looking for ways to control the course of this sometimes wayward support cell.

The motor neurons that control muscles can't survive on their own. They rely on a complicated relationship with another member of the nervous system, cells called astrocytes.

Astrocytes act as sheltering mothers to motor neurons, providing nutrition when needed, keeping their chemical world in balance, protecting them from outside invaders, even physically supporting them. “The motor neurons are very demanding cells,” explains Rafael Radi, an HHMI international research scholar. “They demand from the astrocytes the right growth factors at the right time. Otherwise, they die.”

Defective astrocytes can turn against the motor neurons, however, and are at the root of the muscle-wasting disease amyotrophic lateral sclerosis (ALS), according to recent findings by Radi and his team at the Universidad de la República in Uruguay. Their work, published April 16, 2008, in the Journal of Neuroscience, agrees with findings published in Nature Neuroscience last year by a competing research group from Columbia University.

Even more important, Radi's team has identified a drug that might guide astrocytes back to their nurturing role, a move that they hope can slow or stop the disease's progress. ALS—sometimes called Lou Gehrig's disease—has no treatment. “You cannot grow new motor neurons, but you can prevent new ones from dying,” Radi says. “If our hypothesis is right and we can rescue astrocytes, then they would not kill the motor neurons” and the muscles would be saved.

Photo: Riccardo Cassiani-Ingoni / Photo Researchers, Inc.

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