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Paralyzed Mice and M&Ms

A pill or two might be able to prevent future devastating spinal cord injuries from turning into paralysis, suggests new research on mice.
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In a traumatic spinal cord injury, certain skins of molecules — chondroitin sulfate proteoglycans, or CSPGs, to be exact — bind to the surface of neurons and keep nerve fibers from passing the damaged tissue, a necessary step to recovery. This scarring can leave a victim permanently paralyzed and without significant hope for treatment, suggesting that if the scarring were blocked, nerve regeneration might be possible.

A new research team, headed up by Harvard Medical School Professor John Flanagan, discovered the nerve-cell receptor that these molecules bind to after a spinal cord injury. The molecules in question have a hard sugary coating — a press release from Harvard likened them to M&Ms — which usually means there won't be a receptor.

After experiments in test tubes and Petri dishes suggested such a receptor might exist, researchers poked a hole in the spinal cord of some adult mice missing the receptor (known as protein tyrosine phosphatase sigma, or PTP sigma) giving them a potentially paralyzing injury. Researchers found that within two weeks, neurons were able to send extensions into the fresh scar tissue surrounding the wound — something that wouldn't occur in normal mice. Their work was reported last week in the journal Science.

Adding to the promise, and independent of the Flanagan lab, researchers at McGill University working on spine-damaged mice have reported growth in neurons at the wound site when those mice are missing PTP sigma.

Jerry Silver, a collaborator on the Flanagan project and professor at Case Western Reserve University, said in the release that the discovery suggests that professionals might be able to treat central nervous system injuries in the future with a pill or drug cocktail. There's an estimated 12,000 new injuries in the U.S. each year.

"It's hard to overcome CSPGs in the human body, but receptors may offer an easier target," Flanagan said. "This discovery may lead to treatments that help repair spinal cord injury and may be beneficial to patients with brain injury and neurodegenerative diseases such as Alzheimer's, Parkinson's, Lou Gehrig's, multiple sclerosis and stroke."

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