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THE SENSE OF SMELL/Olfactory Receptor Neurons
& the Scent of Sorrow

The Olfactory Receptor Neuron (ORN) is the workhorse of the nose. They function as sensory cells, detecting the myriad of odors around us. They are also nerve cells and are connected directly to the brain. Researchers and clinicians are attempting to determine how human ORNs translate the chemical fingerprint of odorants into electrical information that can be interpreted by the brain.

At the Monell-Jefferson Taste & Smell clinic, donors contribute ORNs for research projects. One of the leading researchers, Edmund Pribitkin, at the clinic became interested in the sense of smell through his work as a sinus surgeon, "What happens when you operate on the nose and sinuses is that you're altering not only the function of the sinuses but also the sense of smell."

One discovery is this, calcium is involved in the cell's response to stimulation; a change in the amount of calcium in the cell, tells the researchers when a ORN has responded to a particular odor. Human ORNs are different than rats and other animals. Other species always respond to odors with an increase in calcium, a significant number of human ORN cells do the opposite, they show a decrease in calcium concentration after exposure to an odor. Humans also have only about 40% of the number of different olfactory receptors that rats do.

The researchers painstakingly apply odorants to the bowling pin shaped cells and watch computer screen to see the response. By comparing results of other species, human receptors have another unusual characteristic. They are more selective than ORNs from other species. Many rat ORNs will respond to several unrelated odors, where as those from young humans rarely do. This suggests that the way we interpret odor is different than other species.

Another discovery is that despite the fact that we tend to lose our sense of smell as we age, there are as many ORN in older people as there are in younger people, and they are usually more responsive. The hypothesis is that human ORNs become less selective as we age, a single cell may respond to several odors of significantly different chemical structure. These receptors may be in a state of chronic adaptation, and therefore have a functional reduction of sensitivity.

ORNs are directly connected to the brain. When they are stimulated they send a signal to a cell in the olfactory bulb, part of the brain that processes all incoming information about odor. Electrophysiologists can use sophisticated monitoring to study the cells and determine how it functions, by observing the flow of ions (calcium, sodium, potassium) through the cell.
Within the central nervous system, most neurons do not have the capacity to regenerate. ORNs are the exception to that rule, they have the ability to regenerate throughout our life span. Biopsies of the olfactory epithelium (a path of skin within the nose where the ORNs are located) have shown that the less mature cells are found deeper, and they migrate to the surface as they mature. Research in this area is looking into how the ORNs develop and function. It also has implications in the treatment in neurodegenerative disorders, such as Alzheimer's) and traumatic spinal cord or brain injury.

Besides the possible breakthroughs in neuron regeneration, ORN research may provide clues in other disorders. For example, one of the earliest clinical signs of Alzheimer's disease is reduced olfactory function. It is possible that studying what happens in the olfactory neurons, can yield clues as to what is happening in other neurons. Another condition being studied is bipolar (manic-depressive) disorder. bipolar disorder is treated with lithium, but is has yet to be understood how it works. New research shows that there are differences in the calcium response in ORNs of patients before and after they have had their lithium.
Quality of life is another issue to be studied. A large number of people have taste and/or smell disorders. The Monell-Jefferson Taste & Smell clinic is a place where they can come for sensory testing. Many patients are diagnosed with a smell dysfunction. This included many that thought they had a problem with taste. Unfortunately, there are not too many treatments at this time, however, with continued research it is only a matter of time.

The Scent of Sorrow

All of us have had the experience a smell triggering an emotional feeling, or taking us back to a moment in time. Stefan Fatsis, a journalist covering events at the World Trade Center contacted Dr. Dalton at the Monell Clinic after experiencing intense feelings of sadness and grief upon smelling the air around the site. Many New Yorkers had noted a distinct odor in Manhattan, "the scent of devastation." It was not the typical urban smell, but something very bad and unique.

Mr. Fatsis along with Dr. Dalton and two colleagues (none from New York) visited the sight, their reaction to the odor was one of curiosity, but to local people the smell had a profound effect, causing misery, sadness and grief. "It was a bad odor but not the worst I have ever smelled," Dalton recounts. "It was strange and unique and obviously very complex; a burning smell with overtones of rubber - bitter and sweet at the same time. What differed was our emotional reaction. When we smelled it, we were simply curious. But Stefan's demeanor changed completely. It was instantaneous - his shoulders slumped and his face got less animated. You could see that he was miserable."

The group took air samples to study the composition of the odor. This analysis reveled a unique odor, ...'like a soup that had never been mixed before. You had materials that normally you shouldn't have been smelling." The group plans on studying the olfactory function of individuals exposed to this odor.

The researchers were brought in by a journalist, who by training recognized that there was something unique going on related to the odor and his emotional experiences. However, many people do not connect the feelings they are having with the odors they are smelling, and may think they are having a breakdown. The intense work of rescue and emergency workers of all types, firefighters, and combat veterans is usually done under extremely stressful circumstances and all the while they are being exposed to a myriad of sensory information. The same is true for victims of violence and trauma. It is possible for future vivid, emotional memories and anxiety attacks to be triggered by exposure to a similar odor. This fact was recognized by a traumatologist from the Federal Emergency Management Agency, who recently contacted Dr. Dalton. He was working with recovery workers who were exhuming bodies and realized that some of the "potent and frightening emotional memories the workers encountered afterwards might be triggered by odors." At his request Dr. Dalton is developing an informational video designed to train rescue workers and military personal involved in odor-associated traumatic events. The intent is to lessen the impact of these events, by preparing them beforehand. "We hope that we can lessen the impact by preparing these individuals for what may happen to them. Although we still don't know enough to prevent the associations from occurring, I think that just understanding what's happening is a significant way to give people the sense that they're still in control of their mental health and lives,' say Dr. Dalton. She intends to develop a professional production that can be distributed to those who have had trauma associated with an odor.
This work may help scientists gain a better understanding of the relationship between odor and emotions and the physiological response that is triggered. This is an realm that has not been well researched. There are currently studies underway to try and understand psychological and physical symptoms reported by soldiers in the Persian Gulf War. More research is needed to fully understand this area, and also to come up with ways to prevent or reduce the negative associations.

The Monell Connection, Fall 2002.
The Monell Chemical Senses Center Newsletter, October 2001.
Monell Chemical Senses Center 3500 Market Street, Philadelphia, PA 19104-3308. Phone (215) 898-6666.

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without prior permission from The Aromatic Plant Project.
Author's Copyright and Jeanne Rose,

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