Lab Rats Can Fine-tune Their Sense Of Smell
October 31, 2012

Some Animals Are Able To Focus Their Sense Of Smell

Brett Smith for - Your Universe Online

A new study by University of Chicago researchers showed that some animals are able to focus their sense of smell in much the same way that humans can focus their vision.

According to the study that was published in the current issue of the Journal of Neuroscience, the researchers found that laboratory rats were able to adjust their sense of smell by altering their sniffing, which brought scents to receptors in different parts of their nose.

According to study author Leslie Kay, an associate professor of psychology at the University of Chicago, many animals use their specialized sense of smell to detect predators and prey alike.

"Dogs, for instance, are quite dependent on their sense of smell," she said. "But there are many chemicals in the smells they detect, so detecting the one that might be from a predator or an explosive, for instance, is a complex process."

The research performed by Kay and her colleague, Daniel Rojas-Líbano, a postdoctoral scholar at the University of Chile in Santiago, was influenced heavily by two previous studies. In one study, researchers showed that the nose can act like a gas chromatograph in the sense that it absorbs different substances depending on how readily they interact with the sensory receptors in the nose. This study also found that some odorants have high "sorption values," which are easily absorbed into the mucus-laden receptors, while others do not absorb as easily.

The other previous study of interest showed that changes in the airflow entering the nose can affect which odors the nose more readily detects. The researchers found that the structure of the nose allows for different airflows throughout it. These airflows correlate to classes of receptors placed around the nose that are calibrated to detect distinct odors. That study concluded animals might be able change their sniffing patterns to target specific odors within a bouquet of fragrances, similar to the way humans are able to distinguish aroma notes in a fine wine.

To expand upon this previous research, the scientists first attached electrodes to the rats' diaphragm muscles so they could measure their rate of inhalation. They then tested the animals with an assortment of many mixtures of two chemicals to see if they could locate a target scent. Successfully identifying a target resulted in a sugar pellet reward for the rat.

The rats were successful in finding the targets, especially when looking for a highly absorbent odor, which the rat found more quickly than a less absorbent odor.

During their search, the rats´ sniffing patterns depended on which type of odor they were detecting. The animals inhaled for a longer time when they were searching for the low-absorbing odor, and then for a shorter time once they had learned to detect the odor, according to the study.

"What was happening was that the air was moving through the nose at a slower rate and targeting those parts of the nasal epithelium that are further along in the pathway–those more likely to pick up the low-absorbent odors," Kay said.

The research team also found that the animals inhaled more quickly for highly absorbent odorants because the parts of the nose that detect them are closer to the front.

"I think one of the most interesting aspects of these experiments is the finding of the difference in difficulty the rats displayed to detect different targets from the same set of mixtures," Rojas-Líbano said. "This shows that there is more to olfaction than just receptor types and combinations. If detection was solely based on chemical-receptor interactions (as people seem to assume quite often), performance levels should have been more similar between the groups of rats. The physical properties of the odors matter a lot, and so does the type of sniff that an individual uses to smell the odors."