UF scientists hot on scent of sensory discovery

The idea of covering up an embarrassing odor is as familiar as a can of air freshener. But instead of spraying a layer of outdoor freshness atop last night’s fish dinner, imagine discharging a chemical that actually prevents people from ever smelling it at all.

It’s an idea that may alter understanding of the sense of smell, report University of Florida scientists who say their research shows some odors actually turn off smell receptor cells in mammals instead of activating them.

The UF research could aid in the development of tests to diagnose diseases, electronic sensors to detect hazardous chemicals, and treatments for patients who have lost their sense of smell because of illness, said Barry Ache, Ph.D., director of the UF Center for Smell and Taste at UF’s Evelyn F. and William L. McKnight Brain Institute.

“What we may have found could be a fundamental change in understanding of how odors are coded,” said Ache, a distinguished professor at UF’s Whitney Laboratory, the neuroscience department and the zoology department.

Now, the National Institute on Deafness and Other Communication Disorders has awarded $1.5 million to Ache and Asylbek Zhainazarov, Ph.D., a research associate professor at UF’s Whitney Laboratory, to investigate how molecular fats called phosphoinositides interact with other signaling molecules in smell-receptor cells in rats and mice. In people, smell-receptor cells are found in a small patch of tissue high inside the nose, where they communicate with brain cells to process airborne chemical information into meaningful, recognizable scents.

The grant was made on the basis of research done in collaboration with researchers at Ruhr University in Germany and published in the journal Neuron last year. They described how smell-receptor cells taken from rats responded to chemical odors before and after phosphoinositide activity was blocked.

UF scientists began to suspect odors could trigger inhibition of smell-receptor cells in mammals after studying invertebrates such as the Caribbean spiny lobster, Ache said.

“There were only bits and pieces, stuff on the cutting room floor, that this might be going on in mammals,” Ache said. “It looks as if a common biological strategy has been settled on in evolution to detect odors. We want to know more about the strategy so that we can use it to help cure diseases related to sense of smell and to incorporate those principles to build biosensors that will identify chemicals in clinical, industrial and defense applications.”

Chemical biosensors, referred to as electronic noses or e-noses, detect chemical signatures of compounds such as illicit drugs or explosives. They may even be able to tell a supermarket clerk whether a customer is buying a Jonathan apple or a McIntosh.

The task to develop e-noses is formidable because an odor may be a single chemical or a mixture of hundreds or thousands of chemicals. Furthermore, mammals use millions of receptor cells to detect odors, Ache said. The idea that inhibition may occur during the process only adds to the complexity.

“The challenge one faces is detecting subtle differences in complex mixtures against backgrounds that are as or more complex,” Ache said. “But the potentials are enormous for detecting chemical signatures because they can be so specific. The so-called smell of disease has been known since Aristotle’s time.”

Beyond that, a better basic understanding of the sense of smell would help researchers develop therapies for people with smell and taste disorders, Ache said. More than 200,000 people visit a physician each year for help with smell disorders or related problems, according to the National Institute on Deafness and Other Communication Disorders.

An impaired sense of smell is one of the first signs of Alzheimer’s disease. Furthermore, obesity, diabetes, hypertension, malnutrition, Parkinson's disease, multiple sclerosis and even psychological disorders such as depression are all accompanied or signaled by sensory problems like smell disorders.

“Food doesn’t taste as good when someone is on chemotherapy,” Ache said. “Many cancer medications cause smell and taste dysfunctions. In addition to medications, there are enormous causes for clinical smell and taste deficits—the organization of the olfactory part of the brain, for example, is very vulnerable to physical damage accompanying traumatic brain injury.”