The "itch gene" is GRPR (gastrin-releasing peptide receptor), which codes for a receptor found in a very small population of spinal cord nerve cells where pain and itch signals are transmitted from the skin to the brain. The researchers, led by Zhou-Feng Chen, Ph.D. from the Washington University School of Medicine in St. Louis, found that laboratory mice that lacked this gene scratched much less than their normal cage-mates when given itchy stimuli.
Chen's team became interested in GRPR because they were looking for genes in the pain pathway. Among potential pain-sensing genes they identified, GRPR stood out because it is present in only a few nerve cells in the spinal cord known to relay pain and/or itch signals to the brain. "The research was a little disappointing at first," Chen says. "The knockout mice seemed to have the same reactions to painful stimuli as normal mice." But when post-doctoral fellow Yan-Gang Sun, Ph.D., injected the spinal cords of normal mice with a substance that stimulates GRPR, the mice started scratching themselves as if they had a bad itch.
The researchers studied scratching behaviour in two sets of mice — normal mice and GRPR knockout mice. Normal mice scratched vigorously when exposed to a variety of itch-producing substances, but the knockout mice scratched much less. "The fact that the knockout mice still scratched a little suggests there are additional itch receptors," Chen says.
GRPR had been fairly well studied before. "Scientists have been studying this receptor for more than a decade," Chen says. "One interesting thing they've found is that GRPR is implicated in tumour 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."
MEDICA.de; Source: Washington University School of Medicine