NIH Scientists Discover Molecule Associated with Itch

Scientists have discovered a molecule released by the spinal cord that triggers the sensation of an itch. The discovery was made by scientists at the National Institutes of Health who conducted the research on mouse models.

The molecule that is associated with the itch is called natriuretic polypeptide b (Nppb) and it plugs into a specific site in the spinal cord. The signal from the spinal cord then moves through the central nervous system.

When scientists removed Nppb or its nerve cell, they found that the mice no longer felt an itch even after being treated with substances that induce itch.

Mark Hoon, Ph.D., scientist at the National Institute of Dental and Craniofacial Research, and his team began searching for possible triggers of itch with a class of nerve cells that have the molecule TRPV1. These nerve cells or neurons have long projections that extend to the skin, muscle and other tissues and monitor external conditions such as extreme temperatures or pain. However, until recently, researchers had very little idea about how these neurons sent signals via the most appropriate pathway.

It was in Hoon's lab that the study team discovered the neurotransmitters employed by these TRPV1-containing cells. Nppb was one among the several neurotransmitters that the team tested in the lab for detecting the itch sensation.

"We tested Nppb for its possible role in various sensations without success. When we exposed the Nppb-deficient mice to several itch-inducing substances, it was amazing to watch. Nothing happened. The mice wouldn't scratch," said Santosh Mishra, researcher in the Hoon laboratory and lead author of the study, according to a press release.

Researchers also tested the role of another neurotransmitter called GRP associated with itching in previous studies. Hoon's team found that the GRP is also associated with the processing of an itch, but this neurotransmitter begins its work after Nppb has finished sending the signal to the brain.

Researchers said that such a system may even exist in humans and targeting nerve cells that are associated with itch could help millions of people who suffer from chronic itching.

"Our work shows that itch, once thought to be a low-level form of pain, is a distinct sensation that is uniquely hardwired into the nervous system with the biochemical equivalent of its own dedicated land line to the brain," said Mark Hoon, Ph.D., scientist at the National Institute of Dental and Craniofacial Research, part of the National Institutes of Health and senior author of the study.

The study is published in the journal Science.