The tongue’s ability to differentiate between sweet and bitter tastes may reside in the same taste bud cells, a study in the Aug. 2 issue of Proceedings of the National Academy of Sciences reports.
In a study funded by a grant from the National Institutes of Health, researchers conducted experiments on taste bud cells taken from the rear of rats’ tongues, the area that has the highest concentration of taste buds. They isolated single cells from individual taste buds and attached small, fine electrodes to the cells in Petri dishes to record their electrical activity. Researchers also applied a chemical messenger called neuropeptide Y (NPY) to these cells.
They compared the resulting electrical signals given off by NPY to those found in an earlier study they conducted using a peptide called cholecystokinin (CCK).
"NPY activated a completely different signal than CCK did, suggesting that the peptides trigger completely different responses in individual cells," said lead author M. Scott Herness, Ph.D., a professor of oral biology and neuroscience at The Ohio State University.
Researchers also stained some of the cells and viewed them under fluorescent lights using a microscope to see whether both peptides were present. They initially found that NPY is expressed in only a subset of taste bud cells. And every cell that expressed NPY also expressed CCK.
"That surprised us, too," Dr. Herness said. "It may be that these cells release both peptides when something sweet or bitter is on the tongue. CCK might excite the bitter taste and at the same time inhibit the sweet taste, so the bitter message gets to the brain."
Researchers plan on examining how either taste affects individual cells. They think that CCK may override NPY during a bitter sensation, while NPY may override CCK during a sweet sensation. Their next step is to apply bitter and sweet stimuli to taste bud cells that contain both NPY and CCK and see how each peptide reacts.
