If you are one of the millions of people on this planet who suffers from itching you may be pleased to read that scientists at Washington University School of Medicine, St. Louis, have identified the first itch sensation gene. This discovery, say the researchers, may well lead to new treatments which target itchiness precisely – providing relief from severe and chronic itching.
The itch gene is Gastrin-Releasing Peptide Receptor (GRPS), a code for a receptor found in a tiny population of spinal cord nerve cells where pain and itch signals are sent from the skin to the brain.
According to Zhou-Feng Chen, Ph.D., and team, lab mice that did not have this gene scratched themselves much less than normal mice, when an itchy stimulus was given.
The researchers say this study confirms the connection between GRPR and itching. It is the first compelling piece of evidence of a receptor specific for the itch sensation in the CNS (central nervous system).
You can read about this study in the journal Nature.
Itching can be caused by many problems, such as:
Itching can have a dreadfully disruptive effect on many people’s lives – it can mess up your sleep patterns, while scratching can lead to scarring. Patients who suffer from itching have a very narrow choice of treatments.
Chen says “Many genes have been identified in the pain pathway. But itch research has lived in the shadow of pain research, and no one knew which gene was responsible for itching in the brain or in the spinal cord until now.”
Chen and team had been looking for genes in the pain pathway when they became interested in GRPR, which was one of the genes they identified. GRPR stood out because it only exists in very few nerve cells which are known to send pain/itch signals to the brain.
They compared normal mice with mice that lacked the GRPR gene. Chen commented that the research was a little disappointing at first, because the knockout mice seemed to have the same reactions to painful stimuli as normal mice.”
However, when a colleague, Yan-Gang Sun, Pg.D., injected a substance that stimulates GRPR into their spinal cords, the mice started scratching themselves profusely. This observation made them wonder whether the GRPR gene might be involved in the itch sensation.
Two sets of mice were studied. Normal mice and mice without the GRPR gene (GRPR knockout mice). They found that the GRPR knockout mice scratched much less than the normal mice when exposed to itch-producing substances.
Chen believes there are additional itch receptors. As the GRPR knockout mice still scratched a bit, the signal was coming from somewhere. “We know of some proteins that are similar to GRPR, so now we’re trying to determine if there is functional redundancy in the itching pathway,” he said.
Pain and itch are mediated by separate sets of genes in the spinal cord. The researchers came to this conclusion because the GRPR knockout mice had normal reactions to painful stimuli. The good news here is that it is likely that new anti-itching drugs will not have to suppress pain sensation. Pain sensation is a vital protective cue that warns of danger.
“Scientists have been studying this receptor for more than a decade. One interesting thing they’ve found is that GRPR is implicated in tumor growth. As a result of research like this, a lot of substances have been made that block the activity of GRPR. So now researchers can study the effect of these agents on the itch sensation and possibly move that research to clinical applications fairly soon,” Chen added.
“A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord”
Sun YG, Chen ZF. Nature July 25, 2007, advance online publication.
Washington University in St. Louis
Written by: Christian Nordqvist