'Itching' study could help in drug design

US researchers say studying nerve cells associated with itching could result in treatments for chronic itching, sometimes caused by life-saving medications. The finding of a specific set of nerve cells in mice that alerts the brain to itching sensations may settle a decades-long debate about how the body signals the different sensations of itching versus pain, they said. Writing in the journal Nature Neuroscience, scientists at Johns Hopkins University report finding a type of sensory nerve cell whose endings receive information from the skin and relay it to other nerves in the spinal cord. The research in mice suggests that even when the itch-specific nerve cells receive stimuli that are normally pain-inducing, the message they pass along isn't "That hurts!" but rather "That itches!" Pain tells us to withdraw the pained body part to prevent tissue damage, while itch warns us of the presence of irritants, as in an allergic reaction. However, researcher Xinhong Dong said, "when either of these sensations continues for weeks or months, they are no longer helpful. We even see patients stop taking life-saving medications because they cause such horrible itchiness all over." "And sometimes when we try to suppress chronic pain, with morphine for example, we end up causing chronic itchiness," he said. "So the two sensations are somehow related, and this study has begun to untangle them. "Now that we have disentangled these itchy sensations from painful ones, we should be able to design drugs that target itch-specific nerve cells to combat chronic itchiness," Dong said.