Itching is a common annoyance that almost every human being experiences at some time or another. Particularly in the summer, insects, sunburn, and other sources of itch make the discomfort a big part of the season. Now a team of scientists at the National Institute of Dental and Craniofacial Research in Bethesda, Maryland think they know what itching is. Their research has found that the ability to feel itching is associated with a protein called neuropeptide natriuretic polypeptide B.
From the body’s perspective, itching is not pain. The neural signaling pathways for itching and pain are different; someone who is hurting and someone who is itching will use different nerves and parts of the brain to process the sensation. The medical community’s recognition of this distinction began with the 1997 discovery of pruriceptors. Itching is the activation of those pruriceptors; regardless of the ultimate cause of the itching, it is through the pruriceptors that itching is recognized. NPPB, the Maryland team found, is how it is activated. It is through the medium of NPPB that itching is recognized, though a different neurotransmitter is involved in scratching as a response to itch.
Normally NPPB is produced in the heart muscle—a high level is a sign of heart failure, and normal levels are a relatively sure sign that the patient’s heart has not failed. Kidney disease can also lead to excessive NPPB. Its function is to keep the heart going and to protect it from unnecessary changes in operation. It also plays an important role in keeping blood vessels clear and controlling the level of sodium in the blood. Now it appears to be involved in itching as well. In experimental animals bred not to experience itching, NPPB, which is normally found in a variety of mammals in addition to humans, cannot be detected. That indicates that the protein plays a central role in itching.
It would be impractical, of course, to remove the protein from humans, leaving nothing to perform its useful functions. However, researchers are looking at ways to moderate the purireceptor response to NPPB so as to alleviate itching.