Irritating smells alert special cells, NIH-funded s...( If you cook you know. Chop an onion ...)

If you cook, you know. Chop an onion and you risk crying over your cutting board as a burning sensation overwhelms your eyes and nose. Scientists do not know why certain chemical odors, like onion, ammonia and paint thinner, are so highly irritating, but new research in mice has uncovered an unexpected role for specific nasal cavity cells. Researchers funded by the National Institute on Deafness and Other Communication Disorders (NIDCD), part of the National Institutes of Health, describe this work in the March issue of the Journal of Neurophysiology, now available online.

Weihong Lin, Ph.D., of the University of Colorado Denver School of Medicine and University of Maryland, Baltimore County, led the study which discovered that a particular cell, abundant near the entry of many animal noses, plays a crucial and previously unknown role in transmitting irritating and potentially dangerous odors. Dr. Lin and colleagues from both universities plus the Mount Sinai School of Medicine identified the role of this solitary chemosensory cell in transmitting irritating chemical odors in the noses of mice.

Scientists have found similar solitary chemosensory cells in the nasal cavities, airways and gastrointestinal tracts of many mammals as well as fish, frogs and alligators; they think it is likely that they are also present in humans, explains Thomas Finger, Ph.D., one of the senior co-authors at the University of Colorado Denver.

Prior to this work, scientists who study smell and taste thought that irritating odors directly stimulated the trigeminal nerve, which senses touch, temperature and pain throughout the head region, including the delicate membranes that line the inside of the nose. The research team, under the guidance of Diego Restrepo, Ph.D., found that solitary chemosensory cells scattered in the epithelium inside the front of the nose respond to high levels of irritating odors and relay signals to trigeminal nerve fibers.