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July 27, 2007
Everyone knows how unpleasant it is to have an itchy mosquito bite. Itch is one of our defenses against things that might hurt us. However sometimes itching can become chronic from kidney and liver
disease, eczema, a side effect of cancer therapies, or pain killers such as morphine. Currently there are few treatments on the market for clinically serious itching. Now new research, published this week in the journal Nature may change all that.
Scientists at the Washington University School of Medicine in St. Louis have now discovered the gene, GPRR, that controls whether or not the brain receives the message that the skin is itchy. The gene actually codes for a receptor expressed in a very small population of spinal cord nerve cells involved in transmitting pain and itch signals to the brain.
The researchers started out by looking for genes in the pain pathway. They started with GPRR because it's expressed in only a few nerve cells in the spinal cord. So they began to study GPRR knockout mice, that is mice without the gene.
"The research was a little disappointing at first," says Zhou-Feng Chen, who led the research team. "The knockout mice seemed to have the same reactions to painful stimuli as normal mice."
Then, team member Yan-Gang Sun, injected normal mice with a substance to stimulate GPRR. The mice started scratching like mad.
"That's when we thought the gene might be involved in the itch sensation," Chen says. The team studied scratching behavior in normal and knockout mice. Normal mice scratched a lot, and knockout mice significantly less.
Knockout mice reacted normally to pain, suggesting that pain and itch are mediated by different genes along the spinal cord. This is important from a drug development standpoint because ideally you want to suppress itching, but pain can be an important cue warning you of danger.
How close are they to a clinical application? According to Chen scientists have been studying this receptor for over ten years, in fact he says previous research has shown that GPRR is involved in tumor growth. Consequently, a lot of substances have been made that block its activity. Now says Chen, "researchers can study the effect of these agents on the itch sensation and possibly move that research to clinical applications fairly soon."
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