Exposure to Smells Might Protect Olfactory Neurons

People can lose their sense of smell from many causes: a head injury, sinusitis, neurodegenerative diseases like Parkinson's or Alzheimer's, or even old age.

Researchers have now identified a chemical pathway that could help increase the survival of the olfactory sensory neurons that play a vital role in our sense of smell.

Those olfactory neurons, which reside in a layer of epithelium in a mammal's nose, typically die off and are replaced every few weeks. If some of those neurons didn't survive for a longer time, though, animals might forget useful scents, such as a salmon's home stream.

However, scientists know that the olfactory system can adapt, they just didn't know how olfactory neurons themselves participate in that adaptation.

"It's fascinating that we can be sensitized or desensitized to odorants," said Dr. Daniel Storm, UW professor of pharmacology.

Storm's group proposed that some olfactory neurons survived longer than others, allowing an animal or a person to be sensitized to odorants, the volatile chemicals detected through smell. They found that neurons could indeed survive - by being exposed to odorants. Their results appeared in the March 24, 2004 issue of the journal Neuron.

Storm and Dr. William Watt, a former graduate student and now a postdoctoral researcher in the UW School of Medicine, along with other scientists, studied olfactory sensory neurons in mice. They used a harmless virus that labeled the neurons of living mice. The labeling allowed researchers to monitor survival of the neurons after the mouse's olfactory system was exposed to an odorant.

Neurons exposed to an odorant were more likely to survive, even if exposed to conditions that normally causes those cells to die off. Just as important, however, was that they found the chemical pathway that saves olfactory neurons from cell death.

Drugs that activate the chemical chain, known as the Erk/MAP kinase pathway, could be used to protect olfactory neurons from dying off.

"What that suggests is that if you have a situation with a patient losing olfaction, a potential treatment would stimulate that pathway," Storm explained.

Because most people lose about one percent of their sense of smell in every year of their life, older people often have weaker olfactory systems. But olfaction can be lost from Alzheimer's and Parkinson's diseases, head trauma, or sinusitis, a common malady in the cool, rainy Pacific Northwest.

Losing one's sense of smell isn't just a nuisance. It can have serious implications, especially for older people, because it often translates to loss of appetite.

"When you lose olfaction, you just don't want to eat," said Storm. "That can have a big impact on older patients."

The UW and Compellis, a Boston biotech company, have a patent on developing a treatment that would stimulate that chemical pathway and treat the loss of olfaction.