Scientists Discover Olfactory Receptors on the Tongue

By Rita Waimer.

Scientists from the Monell Chemical Senses Center in Philadelphia, Pennsylvania, have found that our senses of smell and taste may be more closely related than was previously thought. Using genetic and biochemical methods, the team discovered key molecules known to exist in olfactory receptors — the sensors that allow our noses to detect odors — in living cultures of taste cells kept alive with methods developed at Monell. They then used calcium imaging to show that olfactory receptor cells and the cultured taste cells responded similarly to odor molecules. Their work was published in the journal Chemical Senses.

The findings suggest that taste and smell begin to combine and inform the flavor of food on the tongue, reinforcing the idea that food tastes like it smells. We’ve long known that the sense of taste lives in the tongue, where it detects sweet, salty, sour, bitter, and savory molecules and helps gauge the nutritional value and potential danger of food. Similarly, we’ve known that the sense of smell lives in the nose, where it provides detailed information about flavor and helps differentiate one food from another.

While we previously thought that our senses of smell and taste were completely separate, combining to form the perception of flavor only once their information reached the brain, the scientists now believe that the two senses actually combine in the mouth. Their new study reveals just how closely linked the two senses are. However, this does not mean that humans can smell with their tongue, and it doesn’t undermine the importance of the nose’s ability to pick up smells and inform the flavor of the food we eat.

"The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odor and taste stimuli on the tongue."

Modifying Flavor with Smell

The scientists, led by Monell cell biologist Mehmet Hakan Ozdener, MD, PhD, MPH, believe their work can help explain how odor molecules modulate taste perception. It could eventually be helpful in developing odor-based taste modifiers that promote healthier eating and reduce consumption of sugar, salt, fat, and other foods that can lead to diet-related diseases like diabetes and obesity. “The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odor and taste stimuli on the tongue,” Ozdener said.

The work could also help scientists better understand how the olfactory system detects odors. There are 400 different types of functional olfactory receptors, but we still don’t know what molecules activate the vast majority of them. These new cultured taste cells respond to odors, so they could possibly be used as screening assays to help identify which molecules bind to specific human olfactory receptors.

The work provides the first demonstration of functional olfactory receptors in human taste cells. In the wake of their findings, the Monell scientists performed more experiments and found that a single taste cell can contain both taste and olfactory receptors. Now the scientists want to see if the olfactory receptors tend to be located with certain taste cells, such as those that detect sour or savory tastes, and study the ways in which odor molecules modify taste cell responses and our perception of taste.