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Itching for treatments that scratching can't always soothe

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American



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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.

Gary Stix, Scientific American's neuroscience and psychology editor, commissions, edits and reports on emerging advances and technologies that have propelled brain science to the forefront of the biological sciences. Developments chronicled in dozens of cover stories, feature articles and news stories, document groundbreaking neuroimaging techniques that reveal what happens in the brain while you are immersed in thought; the arrival of brain implants that alleviate mood disorders like depression; lab-made brains; psychological resilience; meditation; the intricacies of sleep; the new era for psychedelic drugs and artificial intelligence and growing insights leading to an understanding of our conscious selves. Before taking over the neuroscience beat, Stix, as Scientific American's special projects editor, oversaw the magazine's annual single-topic special issues, conceiving of and producing issues on Einstein, Darwin, climate change, nanotechnology and the nature of time. The issue he edited on time won a National Magazine Award. Besides mind and brain coverage, Stix has edited or written cover stories on Wall Street quants, building the world's tallest building, Olympic training methods, molecular electronics, what makes us human and the things you should and should not eat. Stix started a monthly column, Working Knowledge, that gave the reader a peek at the design and function of common technologies, from polygraph machines to Velcro. It eventually became the magazine's Graphic Science column. He also initiated a column on patents and intellectual property and another on the genesis of the ingenious ideas underlying new technologies in fields like electronics and biotechnology. Stix is the author with his wife, Miriam Lacob, of a technology primer called Who Gives a Gigabyte: A Survival Guide to the Technologically Perplexed (John Wiley & Sons, 1999).

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