Estimates suggest 10-20% of people suffer from chronic itch at some time in their lives.
Around 10% of people around the world suffer from eczema - a debilitating condition with symptoms that include intense itching, dryness, redness, weeping, oozing and crusting of the skin.
Eczema is incurable, and many treatments designed to manage it are not very effective.
Writing in the journal Neuron, researchers from the Buck Institute for Research on Aging in Novato, CA, and the University of California, Berkeley (UC-Berkeley) describe how they identified the serotonin receptor HTR7 plays a key role in eczema and other forms of itch.
The team - including neuroscientist Diana Bautista, an associate professor who heads a lab researching the molecular basis of itch, touch and pain at UC-Berkeley - hopes the finding will lead to powerful new therapies for eczema and other chronic itching conditions.
Mice with eczema had less severe symptoms when they lacked HTR7
The researchers became interested in the gene because they noticed in their experiments that the mice that expressed the most HTR7 in nerve cells in the skin were the ones most affected by itch.
Coupled with the fact they already knew from other studies that abnormal signaling of serotonin was linked to eczema and other chronic itch disorders in humans, they decided to investigate further.
They carried out a series of experiments and found HTR7 was involved in chronic itch.
Mice specially bred to develop eczema that lacked the HTR7 gene had less severe skin lesions and scratched less compared with equivalent mice that had the gene.
Prof. Bautista says:
"We are really excited about these results. The dramatic decrease in itching suggests that HTR7 may represent a new drug target for chronic itch."
The team hopes the finding will eventually help develop treatments for people not only with eczema but also other forms of itching conditions, such as psoriasis and allergic itch, since these are also linked to altered serotonin signaling in skin nerves.
Findings may also help reduce side effects of antidepressants
The researchers also mention that one of the side effects of taking antidepressants - which raise levels of serotonin in the skin - can be itching and scratching. They replicated this effect in lab mice by giving them the antidepressant sertraline (Zoloft).
Reducing expression of HTR7 in mice given sertraline caused them to cease scratching, note the researchers.
They believe this finding will be true of humans on antidepressants, since they also express HTR7 in nerve cells in the skin.
Estimates suggest 10-20% of people suffer from chronic itch at some time in their lives. As well as skin conditions such as eczema, chronic itch can arise in other conditions such as kidney failure, some cancers, and cirrhosis.
Funding for the study came from various sources, including the National Institutes of Health and the National Science Foundation.
Earlier this year, MNT learned of another study in the journal Cell that showed how gut microbes are important for serotonin production. Researchers from the California Institute of Technology (Caltech) in Pasadena found that enterochromaffin (EC) cells - one of the three types of cell in the gut that produce serotonin - produce only 40% of their normal levels of serotonin in the absence of gut bacteria.