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NIDCD-funded Researchers Find Missing 'Piece of the Pie' in Understanding Taste

Senior citizen tasting food

Scientists supported by NIDCD are a step closer to unraveling the mystery of taste. In a study published in the December 2, 2005, issue of Science, researchers have pinpointed the chemical responsible for transmitting signals from the taste buds—small sensory bumps on the tongue, throat, and roof of the mouth—to the taste nerves leading to the brain. These findings provide scientists with a more complete picture of this complicated process, helping advance the study of taste and taste disorders.

"People with taste disorders might not be able to enjoy the fun of eating and are at risk for other health problems, such as poorly balanced nutrition, so researchers are working to understand more fully how our sense of taste works," says James F. Battey, Jr., M.D., Ph.D., director of NIDCD. "Until now, there has always been a missing link between the detection of chemicals in the taste buds and the transmission of chemical signals from the taste nerves to the brain. Through an ingenious use of genetic engineering, these researchers have finally been able to solve the puzzle."

Using "knockout mice," mice that are genetically altered to be missing one or more key genes, the researchers were able to narrow the field of possible chemicals to one: adenosine 5'-triphosphate, or ATP, a high-energy molecule that is also important for helping cells in the body to function. The scientists produced mice that are missing the genes that encode two key receptors found in taste nerves—P2X2 and P2X3—both of which bind to ATP. They found that the taste nerves of mice lacking the P2X2 and P2X3 genes showed no response to taste stimulation, although the nerves remained responsive to touch, temperature, and menthol. These results indicate that not only are P2X2 and P2X3 important in transmitting taste signals, but the chemical that they bind to—ATP—is also important. The knockout mice also showed much lower behavioral responses to sweeteners, monosodium glutamate, and bitter substances. What’s more, stimulation of taste buds in a laboratory preparation resulted in the release of ATP, which would be predicted if ATP is involved in the transmission of signals from the taste buds to the taste nerves.

The research was conducted by a team of scientists from the University of Colorado Rocky Mountain Taste and Smell Center, as well as the University of Wisconsin, Colorado State University, and the University of Minnesota.

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