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Itching for treatments that scratching can't always soothe

WASHINGTON, D.C. — Scientists for years have been scratching their heads over the cause of itching. There were theories that it shared a nerve pathway with pain to the brain – and now comes news that different forms of itching apparently have their own neural routes. The question is how to block their way. Sure there are some treatments like Benadryl and its ilk that  stop itching induced by histamines, biological compounds known to cause itching. But no treatments exist for other forms of itching that drive patients to the doctor’s office. 

Despite the fact that itching is the No. 1 complaint that dermatologists receive, there had been little research into the phenom until relatively recently. The reason: the puzzling ailment may be terribly uncomfortable but it's rarely cause for alarm. In certain cases it may be a sign of an underlying problem as serious as cancer – but it was often dismissed because it was not considered to be life threatening.

Researchers over the past decade, however, have begun to take itching seriously – and this week scientists reported at the Society for Neuroscience meeting here on recent research that shows itching uses separate neural pathways to send signals from the skin to the brain. Researchers made this discovery by studying a plant called cowhage, found in Africa and other tropical locales, that is known to induce a non-histamine itching. A compound in the plant, macunain, is the active ingredient in “itch powder” used in gags and was even ingested by the ancients to try to rid the body of parasites.

Ethan Lerner, an associate professor of dermatology at Harvard Medical School, said that he and his colleagues found that mucunain turns on two receptors in nerve cells to produce an itching sensation that could potentially be blocked by meds. “They are classic drug targets,” he says. A drug that shuts down receptors in response to mucunain could also work for at least some other forms of non-histamine itching. But he says pharma companies have yet to express an interest in pursuing such treatments.

Scientists at the University of Minnesota, meantime, have discovered how to scratch what's itching you. Literally. They reported at the meeting that scratching prevents neurons in the spinal cord from responding to an itching sensation, preventing the signal from ever reaching the brain. An understanding of what happens when you scratch may also inspire new forms of treatment that could block these neurons without having to lift a finger to quell that irritating sensation.

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