Contagious disease

Among mice, scratching is catching — as in contagious

itchy mouse
itchy mouse

What happens when you see someone scratch a mosquito bite? You may start to feel an itch come out of nowhere. Then you might start to scratch, too. Mice, new data show, suffer the same strange phenomenon. It’s called contagious scratching.

Tests with mice provide the first clear evidence that contagious scratching can spread mouse-to-mouse, says Zhou-Feng Chen. As a neuroscientist, he studies the brain. He works at the Washington University School of Medicine in St. Louis, Mo. His mice started scratching after watching an itchy neighbor. They even did this after just watching videos of scratching mice.

In discovering this, “there were lots of surprises,” Chen notes. One was that mice would even pay attention to some scratching neighbor. After all, mice are nocturnal. They mostly sniff and use their whiskers to feel their way through the dark. Yet Chen had his own irresistible itch to test the “crazy idea: that mice might share an urge to scratch, he says. And it paid off.

The quirk isn’t just a weird little finding, though. It opens new possibilities for exploring the basis in the brain for picking up such contagious behaviors.

Chen’s group described its new discoveries in the March 10 issue of Science.

How they did it

The researchers housed mice super-itchy mice within sight of some that didn’t scratch much. Then they recorded the animals on video. Shortly after a normal mouse looked at a neighbor scratching, it scratched, too. For a comparison, researchers gave others of these mice a not-very-itchy neighbor. These comparison mice also looked at their neighbor now and then. Rarely, however, would they scratch right after that glance.

And the neighbor didn’t have to be real. Sometimes it was just a mouse video. Animals that viewed the video of scratchers responded the same way. More audience itching and scratching followed the film of a mouse with itchy skin than one…

Scratching is catching in mice

an itchy mouse
Like people, mice experience sudden itches after seeing other mice scratch — a boon for studying the neuroscience of contagious behaviors.

MOUSE SEE, MOUSE ITCH

Catch sight of someone scratching and out of nowhere comes an itch, too. Now, it turns out mice suffer the same strange phenomenon.

Tests with mice that watched itchy neighbors, or even just videos of scratching mice, provide the first clear evidence of contagious scratching spreading mouse-to-mouse, says neuroscientist Zhou-Feng Chen of Washington University School of Medicine in St. Louis. The quirk opens new possibilities for exploring the neuroscience behind the spread of contagious behaviors.

For the ghostly itch, experiments trace scratching to a peptide nicknamed GRP and areas of the mouse brain better known for keeping the beat of circadian rhythms, Chen and colleagues found. They report the results in the March 10 Science.

In discovering this, “there were lots of surprises,” Chen says. One was that mice, nocturnal animals that mostly sniff and whisker-brush their way through the dark, would be sensitive to the sight of another mouse scratching. Yet Chen had his own irresistible itch to test the “crazy idea,” he says.

Researchers housed mice that didn’t scratch any more than normal within sight of mice that flicked and thumped their paws frequently at itchy skin. Videos recorded instances of normal mice looking at an itch-prone mouse mid-scratch and, shortly after, scratching themselves. In comparison, mice with not-very-itchy neighbors looked at those neighbors at…