video: A video of an older mouse experiencing mechanical stimulation. The stimulation evoked scratching behavior in aged mice in a manner not observed in young mice. view more
Credit: J. Feng et al., <em>Science</em> (2018)
The irritating itchiness that affects people as they age and their skin becomes drier may be caused by the loss of Merkel cells, a new study in mice suggests. Jing Feng and colleagues were conducting an experiment featuring a well-established technique whereby light mechanical pressure induces itchiness, when they noticed that older mice scratched more often and more fervently than their younger counterparts. They suspected that Merkel cells, found within skin and which play a key role in conveying the sensation of touch, may be the culprit. (These cells demonstrate similar firing patterns to recently identified receptors in the spinal cord that were found to regulate mechanical itch.) Indeed, the researchers found that mice engineered to have fewer Merkel cells experience greater mechanically induced itch than control mice. Meanwhile, the number of Merkel cells present within skin had no effect on chemical itch or thermal pain. Since people tend to have fewer Merkel cells as they age, the authors suggest that their findings may offer an explanation for the loss of mechanical itch control that's seen under aging and also chronic itch conditions. Amanda H. Lewis and Jörg Grandl discuss these findings in a related Perspective, noting that the idea that fewer sensory neurons are associated with a strong sensation may at first seem counterintuitive; however, in those with fewer Merkel cells, the feeling of an itch may induce an animal to scratch the area and apply pressure, inducing enough activity through remaining Merkel cells and easing the unpleasant sensation. They emphasize that more research is needed to explore this phenomenon in humans.
###
Journal
Science