As common as it is, scratching to relieve an itch has long been considered a biological mystery: Are cells at the surface of the skin somehow tired in need of outside stimulation? Or is the relief of the stimulation centered in the brain?
Perhaps neither one, a new study suggests. Neuroscientists report that specialized cells in the spinal cord appear to be critically involved in producing the feeling of an itch and the feeling of relief after the application of fingernails, at least in healthy individuals.
“It’s a very important study; itching is a major problem for millions of patients,” said Dr. Gil Yosipovitch.
Dr. Yosipoviteh cautioned that the findings may not apply to chronic itches. “But this is the kind of work that should help open this area up to more research.”
The researchers isolated in monkeys cellular(细胞的) connections that run from the surface of the foot to the spinal cord and then to the part for feelings in the brain. They caused the feeling of itchiness by injecting something under the skin. They chose some cells at the base of the spinal cord. Most are sensitive to pain and some to both pain and itchiness. And when the researchers scratched the itchy skin on the monkeys’ feet, it quieted the cell’s activity.
Scientists argue that itching is most likely related to grooming(动物的梳毛), and evolved to protect animals against poisonous plants. But the biology of the itch has been a mystery and ignored for years by researchers who have been far more focused on pain.
It is suggested that itch, like pain, may be a “gated” system where signals from other nerve cells can interfere with the feeling. Scratching the skin near, but not directly on the spot, it often provides relief, just as rubbing an aching arm can reduce pain.
As with some kinds of pain, small reminders of an itching feeling can get people scratching, often without being entirely aware of it. “I give lectures about itching.” Dr. Giesler said, “and I’ll stand up there in front of a whole roomful of people, show a few slides and pretty soon I’ll look out and 90 percent of the audience is scratching.”
Dr. Yosipovitch said there was a long way to go before doctors could expect treatments. For one thing the miserable, chronic itch common in many medical problems most likely involves other mechanisms. “But I feel excited about this finding,” he said. “It’s a sign that this field is really evolving,”