It can be hard to imagine life without a sense of taste. Ice cream would feel cold and smooth without the sweetness. Peanut butter would seem sticky and thick without the nuttiness. Apples would be crispy and juicy without the tartness.

Scientists have long known that different foods stimulate taste buds in our mouths in different ways. Taste buds then send messages along nerves to the brain about the food's flavor.

What's been missing for scientists, however, is an understanding of how these messages about taste get from taste buds in the tongue to the body's nervous system.

Now, researchers from Colorado State University in Fort Collins and elsewhere say that they have found the flavor messenger. A molecule called adenosine 5'-triphosphate (ATP) seems to be the missing link.

ATP normally works to store and transport energy within cells. Scientists had noticed that ATP occasionally also works as a neurotransmitter, a molecule that sends messages from one nerve cell to another. In some cases, for example, it takes information about the amount of oxygen in your blood and tells your nerves what it has found.

To see whether ATP could also carry information about flavor, the scientists first studied taste buds that had been taken out of normal mice. When stimulated with flavored liquids, the buds released ATP.

Next, the team worked with mutated mice that were unable to transport ATP into cells. The nerves in these mice reacted to touch, but did not respond to flavor chemicals.

Finally, the researchers put mice in cages with two water bottles. One bottle held water. The other held different types of flavored liquids. The results showed that normal mice liked some of the flavored drinks better than water. Some, they liked less. The mutated mice, on the other hand, couldn't tell the difference between water and the flavored liquids. They drank any one liquid as often as the others.

The findings suggest that ATP is the reason that you can tell the difference between chocolate pudding and mud. Life without it as a taste messenger would be a lot less interesting.—E. Sohn