Finding challenges accepted view of MS: Unexpectedly, damaged nerve fibers survive

February 6, 2013 by David Tenenbaum
Finding challenges accepted view of MS: Unexpectedly, damaged nerve fibers survive
Spinal-cord tissue from normal (left) and mutant (right) rats. The normal tissue show a thick, effective layer of myelin insulation needed for normal nerve signaling. The mutant rats have no myelin, but surprisingly, the axons (long nerve fibers) remain intact. Credit: Chelsey Smith and Ian Duncan, UW-Madison

(Medical Xpress)—Multiple sclerosis, a brain disease that affects over 400,000 Americans, causes movement difficulties and many neurologic symptoms. MS has two key elements: The nerves that direct muscular movement lose their electrical insulation (the myelin sheath) and cannot transmit signals as effectively. And many of the long nerve fibers, called axons, degenerate.

Many scientists believe that axons are doomed once they lose the insulation, but a new study by graduate student Chelsey Smith and former undergraduate Elizabeth Cooksey in the Journal of Neuroscience shows axons can survive for long periods in rats even after losing myelin.

"This was the first study to demonstrate long-term axon survival after myelin ," says senior author Ian Duncan, a professor in the School of Veterinary Medicine at the University of Wisconsin-Madison.

The mutant rats in the experiment have substantial myelin at first, but by eight weeks the essential myelin insulation is lost. "It was surprising," says Duncan, an expert in MS pathology. "Nine months is a relatively long period in a rat's lifetime, and there wasn't a loss of axons, so the assumption that axons must automatically die without myelin seems incorrect."

Normally, insulating myelin is made by supportive cells called oligodendrocytes that live alongside the axons. Duncan observes that oligodendrocytes and related cells also assist by secreting that neurons may need to survive. "That is just speculation, but in our study, the oligodendrocytes were found in much greater numbers, probably in an attempt to produce more myelin, and we saw an overall increase in growth factor production."

Although oligodendrocytes definitely produce growth factors during early development in the rat, this study identified three neural growth factors that are produced by these in the older animals. "This paper was the first to show that continue to express growth factors in mature animals, and that could be important," Duncan says.

Growth factors are proteins that stimulate a wide range of growth and development, and their absence has been implicated in several neurological diseases. Duncan says more study of growth factors could suggest a route to preventing nerve fiber loss in MS and other myelin diseases.

Although other researchers have found that axons survive in mutant mice that fail to make myelin, Duncan notes that those animals lived only four months. "This survival was more than double that; it's a significant increase."

Scientists have known for decades that axons degenerate and disappear in MS, and that idea is now a major focus of scientific interest. "Much in vogue is the idea that you have to protect axons above and beyond everything else, that MS is not primarily a demyelinating disease, it's primarily an axonal disease," Duncan says. "Our finding shows that it is not absolutely certain that axons will degenerate when they are demyelinated. If we are correct in our speculation, we could potentially protect the axon if we can increase the amount of growth factor being produced by the helper cells."

Explore further: Glial cells assist in the repair of injured nerves

Related Stories

Glial cells assist in the repair of injured nerves

January 28, 2013
When a nerve is damaged, glial cells produce the protein neuregulin1 and thereby promote the regeneration of nerve tissue.

Brain electrical activity spurs insulation of brain's wiring

August 11, 2011
(Medical Xpress) -- Researchers at the National Institutes of Health have discovered in mice a molecular trigger that initiates myelination, the process by which brain cell networks are reinforced with an insulating material ...

Scientists identify inhibitor of myelin formation in the central nervous system

November 20, 2012
Scientists at the Mainz University Medical Center have discovered another molecule that plays an important role in regulating myelin formation in the central nervous system. Myelin promotes the conduction of nerve cell impulses ...

Recommended for you

The neural codes for body movements

July 21, 2017
A small patch of neurons in the brain can encode the movements of many body parts, according to researchers in the laboratory of Caltech's Richard Andersen, James G. Boswell Professor of Neuroscience, Tianqiao and Chrissy ...

Faulty support cells disrupt communication in brains of people with schizophrenia

July 20, 2017
New research has identified the culprit behind the wiring problems in the brains of people with schizophrenia. When researchers transplanted human brain cells generated from individuals diagnosed with childhood-onset schizophrenia ...

Scientists discover combined sensory map for heat, humidity in fly brain

July 20, 2017
Northwestern University neuroscientists now can visualize how fruit flies sense and process humidity and temperature together through a "sensory map" within their brains, according to new research.

Scientists reveal how patterns of brain activity direct specific body movements

July 20, 2017
New research by Columbia scientists offers fresh insight into how the brain tells the body to move, from simple behaviors like walking, to trained movements that may take years to master. The discovery in mice advances knowledge ...

Team traces masculinization in mice to estrogen receptor in inhibitory neurons

July 20, 2017
Researchers at Cold Spring Harbor Laboratory (CSHL) have opened a black box in the brain whose contents explain one of the remarkable yet mysterious facts of life.

Speech language therapy delivered through the Internet leads to similar improvements as in-person treatment

July 20, 2017
Telerehabilitation helps healthcare professionals reach more patients in need, but some worry it doesn't offer the same quality of care as in-person treatment. This isn't the case, according to recent research by Baycrest.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.