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Nerve cells could block urge to scratch: neurons in spinal cord may curb itch caused by light tap on skin.

A fly tickling your arm hair can spark a maddening itch. Now, scientists have spotted nerve cells in mice that curb this light twiddling sensation. If humans possess similar itch-busters, the results, published in the Oct. 30 Science, could lead to treatments for the millions of people who suffer from intractable, chronic itch.

For many of these people, there are no good options. "This is a major problem," says Gil Yosipovitch, a clinician at the Temple University School of Medicine in Philadelphia and director of Temple Itch Center. The new study shows that mice handle an itch caused by a fluttery touch differently than other kinds of itch. This distinction "seems to have clinical applications that clearly open our field," Yosipovitch says.

Scientists have made progress teasing apart the pathways that carry itchy signals from skin to spinal cord to brain (SN: 11/22/08, p. 16). Those signals often originate from chemicals, such as those delivered by mosquitoes. All that's needed to spark a different sort of itch, called mechanical itch, is a light touch on the skin. Mechanical itch may help explain why clothes or dry skin can be itchy.

The new finding comes from mice engineered to lack a type of spinal cord nerve cell. These mice "have the urge to scratch all the time," says study coauthor Qiufu Ma, a neuroscientist at Harvard Medical School. A light touch from a filament caused the itchy mice to scratch themselves more than regular mice.

But the mice appeared normal in other ways: They responded to pain and itchy chemicals in the same way normal mice do, suggesting the body has a dedicated, specific way of detecting mechanical itch, Ma says.

If a light touch taps into the itch accelerator, then these nerve cells are the brakes, says coauthor Martyn Goulding, a neuroscientist at the Salk Institute for Biological Studies in La Jolla, Calif. Removing these nerve cells lets the itch signal proceed unchecked, he says.

By finding these nerve cells, scientists can start to piece together the rest of the pathway that detects and carries these itch signals to the brain, Goulding says.

It makes sense that human skin would develop the ability to detect an itchy tickle, he says. "If you have parasites or disease-bearing insects that are on your skin biting you, they might introduce pathogens," he says. A quick scratch, prompted by an itch, could prevent that.

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Title Annotation:BODY & BRAIN
Author:Sanders, Laura
Publication:Science News
Article Type:Report
Date:Nov 28, 2015
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