Nerves and Itching

Byron's Comments:

A specific nerve signal is associated with itching.

Study Title:

Cellular Basis of Itch Sensation

Study Abstract:

Itch and pain are two distinct sensations. Although our previous study suggested that gastrin-releasing peptide receptor (GRPR) is an itch-specific gene in the spinal cord, a long-standing question of whether there are separate neuronal pathways for itch and pain remains unsettled. Here, we selectively ablated lamina I neurons expressing GRPR in the spinal cord of mice. These mice showed profound scratching deficits in response to all of the itching (pruritogenic) stimuli tested, irrespective of their histamine-dependence. In contrast, pain behaviors were unaffected. Our data also suggest that GRPR+ neurons are different from the spinothalamic tract (STT) neurons that have been the focus of the debate. Together, the present study suggests that GRPR+ neurons constitute a long-sought labeled line for itch sensation in the spinal cord.

From press release:

Researchers have found specific nerve cells responsible for itchiness, a discovery that could lead to better treatments for skin conditions.

Experiments on mice show they have nerve cells that convey only an itch sensation—contradicting common wisdom that itch and pain are closely related.

Reporting in the journal Science, researchers at Washington University School of Medicine in St. Louis and Peking University Third Hospital in Beijing said they created itch-free mice by killing their itch-specific neurons.

“This finding has very important therapeutic implications,” Washington University’s Zhou-Feng Chen, who led the study, said in a statement.

“We’ve shown that particular neurons are critical for the itching sensation but not for pain, which means those cells may contain several itch-specific receptors or signaling molecules that can be explored or identified as targets for future treatment or management of chronic itching.”

Eczema, psoriasis, allergies, infections and other conditions can cause chronic itching and various treatments are often only partially effective.

In 2007 the researchers identified the first itch gene called gastrin-releasing peptide receptor, or GRPR. It was active in the spinal cord.

“But the identification of an itch receptor in spinal-cord neurons didn’t mean those neurons were itch-specific because it was possible that they also could have pain-related genes,” Chen said.

So they destroyed nerve cells that had active GRPR, using a toxin that attaches to GRPR and injecting it into the spinal cords of mice.

When the mice then were exposed to things that caused itching, they did not scratch. But they felt pain.

“This is a very striking and unexpected result because it suggests there is an itch-specific neuronal pathway in the spinal cord,” Chen said.

“We’ve shown that these GRPR neurons are important for itching sensation and not for pain, but we really don’t know much more about them,” Chen said. “We still have a lot of questions, and we are very interested to find more answers.”

Study Information:

Yan-Gang Sun, Zhong-Qiu Zhao, Xiu-Li Meng, Jun Yin, Xian-Yu Liu, and Zhou-Feng Chen Cellular Basis of Itch Sensation Science 2009 August 
Washington University School of Medicine in St. Louis and Peking University Third Hospital in Beijing.

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