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Why is it so hard to ignore an itch?

Kathleen Blanchard's picture
Mouse study dissects why we have to scratch an itch.

Scientists finally understand what events happen in the body that tells our brain we have an itch we just have to scratch.

According to the finding, the culprit behind itching is a molecule called natriuretic polypeptide b (Nppb) that is hardwired to go straight to our brain.

Mark Hoon, a scientist at the National Institute of Dental and Craniofacial Research, part of the NIH and his team studied mice to find the underpinnings of itching, also known as pruritus.

The finding is important because itching can become a source of angst for some people who have chronic issues and feel the need to scratch to the point that quality of life is interrupted.

Causes of itchy skin include psoriasis, eczema. Some people experience chronic pruritus from underlying health problems like kidney, thyroid and liver disease.

Most of us experience an itch in one place, but for some patients with chronic illness, itching can involve the whole body.

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For their study, researchers looked at neurons that transmit signals related to itching; starting with neuron cells that are the monitors for heat, cold and pain. The neurons also have a molecule called TRPV1 that the scientists honed in one. Itching is believed to be a type of pain.

Next they screened for neurotransmitters including those that contained Nppb to find out which ones transmitted sensation.

Santosh Mishra, lead author on the study and a researcher in the Hoon laboratory explained testing for Nppb’s role in various sensations was unsuccessful. Mice deficient in the molecule would not scratch, even when they were exposed to substances that cause itching.

Upon further testing, the researchers discovered Nppb is the molecule necessary to induce itching in addition to getting the body to respond to itchy substances.

When they removed the NppB receptor neurons from the spinal cord, they discovered there was no change in other sensations, but itching went away.

Hoon said the discovery means now researchers know the first 3 steps in what causes what is medically known as pruritus, or itching. Nppb is also used by the heart and other parts of the body. Interfering with the itching pathway could have negative consequences.

The next step is to uncover the pathway that causes pruritus in humans in hopes of finding ways to ‘turn off’ itching without causing harm. The study authors say the finding about what happens that makes us have have to scratch an itch is a start, but there is still more to be learned to help humans suffering from chronic skin disorders and other ailments that affect skin sensation.