The relationship between NPY and CCK may provide the answer. A few years ago, Herness' laboratory was the first to find CCK in taste bud cells. These results suggested that CCK may tell other cells ?those attached to nerve fibers that transmit messages to the brain ?that a bitter taste was on the tongue.
In the current study, the researchers conducted their experiments on taste bud cells taken from the rear of the tongues of rats. (The back of the tongue has the highest concentration of taste buds.) They isolated single cells from individual taste buds. They attached very small, fine electrodes to these single cells in Petri dishes in order to record the electrical activity of each cell. They also applied NPY to these cells. Cells are like tiny batteries, as each has its own electrical charge.
They compared the resulting electrical signal given off by NPY to what they had found in the earlier work on CCK.
"NPY activated a completely different signal than CCK did, suggesting that the peptides trigger completely different responses in individual cells," Herness said.
The researchers also stained some of the cells in order to see whether or not both peptides were present. This procedure uses fluorescent light to let researchers actually see the peptides under a microscope.
They initially found that NPY is expressed in only a subset of taste bud cells. Yet every cell that expressed NPY also expressed CCK.
"That surprised us, too," 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."
Although the researchers did not examine how either taste affected individual cells
Source:Ohio State University