Johns Hopkins researchers have uncovered strong evidence that mice have a specific set of nerve cells that signal itch but not pain, a finding that may settle a decades-long debate about these sensations, and, if confirmed in humans, help in developing treatments for chronic itch, including itch caused by life-saving medications.
At the heart of their discovery is a type of sensory nerve cell whose endings receive information from the skin and relay it to other nerves in the spinal cord, which then coordinates a response to the stimulus. Published online Dec. 23 in Nature Neuroscience, a report on the research suggests that even when the itch-specific nerve cells receive stimuli that are normally pain-inducing, the message they send isn’t “That hurts!” but rather “That itches!”
Pain and itch are both important sensations that help organisms survive. And pain is arguably more important because it tells us to withdraw the pained body part in order to prevent tissue damage. But itch also warns us of the presence of irritants, as in an allergic reaction. However, “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,” says Xinzhong Dong, a Howard Hughes early career scientist and associate professor of neuroscience at the Institute of Basic Biomedical Sciences at the Johns Hopkins University School of Medicine. “And sometimes when we try to suppress chronic pain, with morphine for example, we end up causing chronic itchiness. So the two sensations are somehow related, and this study has begun to untangle them,” he says.