Daffodil International University
Faculty of Engineering => EEE => Topic started by: Kazi Taufiqur Rahman on November 23, 2015, 11:40:33 PM
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A fly tickling the hair on your arm can spark a maddening itch. Now, scientists have spotted nerve cells in mice that curb this light twiddling sensation. If humans have similar itch-busters, the results could lead to treatments for the millions of people who suffer from chronic, unstoppable itch.
For many of these people, there are currently no good treatments. “This is a major problem,” says Gil Yosipovitch. He directs the Temple University Itch Center in Philadelphia, Pa., and was not involved in the new study.
All touch sensations — including itch — start at the skin. In recent years, scientists have started to learn how nerve cells carry itchy signals from there to the spinal cord and on up to the brain. Often the original itch signal is triggered by chemicals, such as those that mosquitoes inject. For another sort of itch, all that’s needed is a light touch on the skin. That’s called a mechanical itch. The fact that this type of itch exists is no surprise, Yosipovitch says. Mechanical itch may help explain why clothes or even dry, scaly skin can be so itchy. It’s also why you might feel a mosquito crawling on your skin before it takes a bite.
The new study, published October 30 in Science, involved mice with one key defect. Scientists had altered their genes so that they lacked a certain type of nerve cell in their spinal cords. Without those cells, the mice “have the urge to scratch all the time,” says study coauthor Qiufu Ma. He’s a neuroscientist at Harvard Medical School in Cambridge, Mass. Even with nothing specifically causing them to itch, the mice scratched so often that they developed bald patches on their skin. A light touch from a thin wire will cause a mechanical itch. This touch led the mice to scratch themselves more than regular mice did. Yet the itchy mice responded to pain and itch-causing chemicals normally.
That suggests some nerve cells detect only mechanical itch, Ma concludes. If a light touch taps into the itch accelerator, then these spinal-cord nerve cells act as the brakes, says Martyn Goulding, who also worked on the study. He’s a neuroscientist at the Salk Institute for Biological Studies in La Jolla, Calif. Removing these nerve cells lets the itch signal more easily get through to the brain, he says.
The discovery of itch-blocking nerve cells opens up new possibilities for understanding itch, Goulding says. Now, scientists can start to piece together the rest of the nerve pathway that detects mechanical itch on the skin and then carries that signal to the brain. These nerve cells produce a chemical signal called neuropeptide Y. Future experiments can test what role that chemical plays in how a mechanical itch makes itself known, he says.
It makes sense that human skin would develop the ability to detect an itchy tickle, Goulding says. An insect crawling on your skin could be harmless. But if it’s carrying germs and bites you, it might cause a nasty infection, he says. A quick scratch, prompted by an itch, might prevent that.
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Thanks for sharing