Unpleasant odor endangers special olfactory cells

You probably know how to act on your own will cause you to shed tears when a burning sensation enters your eyes and nose. Although scientists do not know why certain chemical odors such as onions, ammonia and paint smells are so uncomfortable, a new study done on mice has recently discovered a Unexpected role for nasal cavity cells.

Dr. Weihong Lin of Colorado Denver Medical University and the University of Maryland (Baltimore County) directed the study to discover that a particular cell in many animals present in the immediate vicinity of the nostril plays a key role first. that is not known for transporting offensive odors that are potentially dangerous. Dr. Lin and colleagues from both universities, in addition to his colleague from Mount Sinai Medical School, discovered the role of this single olfactory cell in transporting chemical odors. irritating in the nasal cavity in mice.

The same solitary cells were also detected in the nasal cavity, airways or gastrointestinal tract in many mammals, as well as fish, frogs and crocodiles. According to Dr. Thomas Finger, one of the principal co-authors of the University of Colorado Denver, it seems that this cell is also present in humans.

Before conducting this study, the scientists used to study the taste that irritated odors directly stimulated the trigeminal nerve (sensory nerves, temperature and pain sensation). around the head area), and also delicate fragile membranes located inside the nasal cavity. The team, led by Dr. Diego Restrepo, found that single olfactory cells scattered in the epithelium inside the nasal cavity (but near the nostril) reacted when the odors were offensive. high, then transfer the signal to the trigeminal nerve .

(Photo: iStockphoto) Dr. James F. Battey - Director of NIDCD - said: 'This interesting study has brought the right direction to the previous false assumptions about how unpleasant odors are received. , thereby expanding our understanding of the sense of smell. Extensive investigation can bring deeper knowledge to help explain why humans are sensitive to unpleasant smells. '

Solitary olfactory cells located on the surface of the nasal cavity are closely related to the trigeminal nerve located just below the surface. Initial research has shown that these cells contain receptors for bitter taste and bitter substances on the surface of the nasal cavity that stimulate trigeminal neural reflexes. Surprised, Dr. Restrepo and Finger decided to find out whether single olfactory cells reacted to offensive odors. By using nasal tissue taken from mice, they examined a series of changes that occurred in those cells when they exposed them to some unpleasant chemical odors with high concentrations.

Among the phenomena they observed were electromagnetism in cells that showed that the cells also responded to external stimuli. There are also changes in the density of calcium ions in the cell to signal other cells. Their experiments proved that single olfactory cells responded to stimulation from chemical odors and sent information to trigeminal nerves.

When stimulated, the trigeminal nerve will transmit a painful, burning sensation that triggers a self-defense reflex such as vomiting or coughing. The architecture of the nasal tissue with single olfactory cells on the surface in combination with the trigeminal nerve located just below allows the nose to recognize a lot of offensive odors.

Fortunately, the response threshold is quite high, so if you are exposed to a small amount of unpleasant chemical odors (such as the smell emitted by some fruits), it will not cause us to vomit or cough. For example, there are two types of odor chemicals, citral and geraniol, in citrus, but the ratio of these two substances is too low to cause self-defense reflexes. Only smells with high proportions can be dangerous to cause self-defense reflexes.

Researchers point out that their findings provide additional examples for the Law of Specific Neuroscience drafted by Johannes Peter Muller in 1826. Muller says that the way we receive stimuli depends on the god system. experience is not stimulating itself . In the case of offensive odors, we feel like this is because they are transmitted through the trigeminal nerve, making the brain understand the information conveyed like an aching pain rather than a chemical odor.

According to the researchers, their results raise new questions about how to identify offensive odors. In addition, further research is needed to find out whether programmed olfactory cells recognize certain specific stinging agents, which receptors are involved. stimulated, at the same time, explored the steps that these cells use to convert chemical stimuli into a signal to the trigeminal nerve.

The research was funded by the National Institute of Hearing Impaired and Disorders of the National Institutes of Health. The study will be explained online in the March issue of Neurophysiology.