The smell of dough rising in the oven and the first crunch of home-baked sourdough bread is a divine experience for many us. But what exactly is it that allows us to indulge in such a sensory experience? It seems some of that oh-so-sublime gluttony may involve smell receptors in the nose that are also found in human taste cells on the tongue.
Writing in the journal Chemical Senses, a team of scientists propose that our sense of taste and smell “cross-talk” before reaching the brain in the first study of its kind. Previous evidence suggested the two senses sent separate signals to the brain that then converged and formed our perception of food. The researchers from the Monell Center instead suggest they may interact before even reaching the brain.
"Every step of this work made me surprised and excited," said study senior author Mehmet Hakan Ozdener, a cell biologist at Monell, in an interview to IFLScience. "My lab is the only one in the world able to culture taste cells in-vitro (tongue in the dish) with complete molecular and physiological properties. However, this discovery is completely unexpected and provides new research avenues to the scientist."
The receptors on our tongue are responsible for salty, sweet, sour, bitter, and umami sensations – with a possible sixth sense thrown in. They are not, however, the sole players. Our sense of smell plays a large part too, as those who have pinched their nose shut while eating will have discovered.
For the study, the team probed taste cell cultures using genetic and biochemical methods. They then used calcium imaging to reveal that taste cells respond to odor molecules in much the same way that olfactory receptor cells do. This suggests some of our taste cells may contain molecules present in olfactory receptors.
"It is known that olfactory receptors and gustatory (taste) receptors are located in two different anatomical locations," said Ozdener. "It is believed that the cross-talk/interaction between these two independent gustatory and olfactory sensation occurs centrally, in the anterior Insula region of the brain. However, with this study, we demonstrated that the interaction between olfactory and taste senses may take place at the periphery, on the taste cells."
Taste receptors found on the tongue have also been discovered in the pancreas, respiratory system, lungs, testicles, urinary bladder, and spermatozoa. Just because the receptors are there, it doesn’t necessarily mean we taste with them in the same way. For example, if we inhale something bitter, we may cough and the receptors in our lungs fire.
Ozdener added: "The presence of functional olfactory receptors on taste cells may point to new directions in the manipulation of food flavor to reduce the risk of extreme obesity by controlling overeating in genetically predisposed subjects."
Previous studies have found smell receptors in cDNA libraries from the whole tongue, but this study actually demonstrates it. The results are only preliminary and were tested in live cell cultures from humans and mice. There are more than 400 olfactory receptor genes, so further studies are needed to understand the entirety of the system.