Scientists Find Nerve-Muscle Signals Go Both Ways

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Scientists Find Nerve-Muscle Signals Go Both Ways

http://www.mdausa.org/

Researchers in the laboratory of MDA-supported Lin Mei at the Medical

College of Georgia in Augusta have found that muscle fibers do more

than passively receive signals from nerve fibers that tell them to

contract or relax.

Instead, say Mei and colleagues, who published their findings online

today in Nature Neuroscience, " backwards " (retrograde) signals coming

from muscle fibers to nerve fibers profoundly influence nerve-fiber

location and function.

When the investigators bred mice lacking a protein called beta-

catenin in their muscles, they saw that branches of the phrenic

nerves, which go to the respiratory diaphragm, were mislocated in the

diaphragm muscle and that signal transmission was reduced.

However, when beta-catenin was depleted only in nerve cells in the

mice, they didn't have this type of neurological problem.

" These observations demonstrate that muscle beta-catenin is a key

ingredient for neuromuscular junction formation, " Mei said, referring

to places where nerve and muscle fibers meet. The findings also

showed that beta-catenin may control other proteins necessary to

nerve-cell health, she added.

" Muscles are known to produce elusive nutritional factors for nerve-

cell survival and development, " Mei said. " And these findings could

provide leads to their identification. "

They could also have implications for a variety of neuromuscular

diseases, including amyotrophic lateral sclerosis (ALS), the

investigators note. In the vast majority of cases of this paralyzing

and fatal disease, nerve cells that control muscle fibers die from

unknown causes, some of which probably have their origins outside the

ill-fated nerve cells themselves.

In an accompanying editorial, researchers from Hong Kong University

of Science and Technology describe the findings' significance

as " several-fold. " They say these experiments will help scientists

understand more about how neuromuscular junctions develop and may add

to current understanding of neuromuscular disorders, including ALS

and muscular dystrophy.