"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. "That's when we thought the gene might be involved in the itch sensation," Chen says. "So we began to systematically investigate this possibility."
They studied scratching behavior 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. "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."
GRPR knockout mice had normal reactions to painful stimuli, indicating that pain and itch are mediated by separate sets of genes in the spinal cord. This suggests that drugs can be used to suppress the itch sensation without affecting the pain sensation, according to Chen. And because pain can be an important protective cue that warns of danger, it may be a distinct advantage to have an anti-itch medication that doesn't compromise our pain-sensing capability.
GRPR had been fairly well studied before, but no one could provide a compelling link between GRPR and itching before now. "Scientists have been study
Source:Washington University School of Medicine