How Scratching Curbs the Itch?

Itching brings with it that ever-increasing urge to scratch, which always works wonders, but not much is known about the physiological  mechanisms behind this phenomenon.

Now scientists have watched spinal nerves transmit that relief signal to the brain in monkeys, a possible step toward finding new treatments for persistent itching in people.
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Nerve cells play a key role in itching

More than 50 conditions can cause serious itching, including AIDS, Hodgkin’s disease and the side effects of chronic pain treatment, said Glenn Giesler, a neuroscientist at the University of Minnesota in Minneapolis. Some terminal cancer patients even cut back on pain medication just to reduce the itch, he said.

Scratching can lead to serious skin damage and infections in people with chronic itch, he said. So scientists want to find ways for such people to relieve their distress “without tearing up their skin,” he said.

While medications can relieve some kinds of itch, other cases resist current treatments.

Nobody knows just how scratching relieves itch. But the federally funded monkey study, reported Monday on the website of the journal Nature Neuroscience by Giesler and colleagues, takes a step in unraveling the mystery.

The scientists focused on a kind of spinal nerve that transmits the “itch” signal to the brain. The researchers sedated long-tailed macaques for the experiment and placed recording electrodes on their spinal nerves. They injected a chemical into a leg to produce itching. The nerves fired electrical signals in response. Then the researchers scratched the leg with a hand-held metal device that simulates three monkey fingers. The firing rate dropped — the apparent signature of the “relief” signal. In contrast, when researchers scratched the leg without causing an itch first, the firing rate jumped. So the nerves somehow “know” to react much differently if there’s an itch to be relieved than if there isn’t.

Sources: The Times Of India

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