Why wool sweaters cause itchiness

Presumably, the researchers noted, because MrgA3 cells are only a small fraction of all pain-sensing nerve cells, the mice had normal withdrawal responses to painful stimuli like hot water.

However, when exposed to itchy stimuli, their scratching responses were reduced to varying degrees depending on the stimulus, most significantly in response to chloroquine. The fact that some stimuli still caused scratching suggested to the scientists that MrgA3 cells are not the only ones in the body that respond to itch.

"We were convinced that MrgA3 cells are responsible for much of the sensation of itch, but it wasn't yet clear whether MrgA3 cells could also relay painful information," Dong said.

In their final experiments, the scientists used genetic techniques to create mice in which the MrgA3 cells were the only cells in the body capable of responding to capsaicin, that peppery pain-inducing substance.

When injected into the cheeks of mice, normal mice massage the area with their forepaws to relieve the hot sensation. When injected into the experimental mice, they vigorously scratched their cheeks with their hind legs, suggesting that this normally painful stimulus had been communicated to the brain—by MrgA3 cells—as itchiness.

"Now that we have disentangled these itchy sensations from painful ones, we should be able to design drugs that target itch-specific nerve cells to combat chronic itchiness," Dong said.

"We hope that this will not only provide relief, but also increase people's faithfulness to their drug plans, particularly for deadly diseases like malaria and cancer," Dong added.

The study has been published online in Nature Neuroscience.

ALSO READ

Dogs experience 'runner's high' like humans

An exotic way to use mangoes in a salad

Healthy diet and lifestyle essential to battle the bulge

Do you need mastectomy?