Water does not taste tasteless, how do we feel?

Have you ever wondered why water is tasteless but we can still distinguish water between many other liquids?

When viewed under a microscope, our tongue is like the surface of a strange, rugged planet with taste buds.

The tongue receives five basic tastes: salty, sour, sweet, bitter and umami. But perhaps mammalian taste buds are also capable of sensing the sixth taste - feeling water , thereby adding a voice to the debate that has lasted for centuries: whether the country has its own taste Or is it just an environment for others?

Insect and amphibian animals have nerve cells that sense water. Patricia Di Lorenxo - a behavioral neuroscience scientist at Binghamton University (part of the New York State University system) - said the evidence gradually shows that there are similar cells in animals. breast.

Specifically, some recent brain scan studies suggest a region of the human cortex that is particularly reflective of water.

Cells containing acid receptor receptors are thought to help us identify the taste of water - (Istockphoto image).

In previous studies, Zachary Knight - a neuroscientist at the University of California, San Francisco, and his colleagues have found a special amount of neurons in the hypothalamus that create a feeling of thirst, and at the same time give rise to When animals start or stop drinking water.

However, the brain must have received information about the presence of water from the mouth and tongue, because when the animal stops drinking water for a long time the signal comes from the intestine or from the blood to let the brain know the body. Thirsty.

In an attempt to resolve the question of whether the human tongue sensed the taste of water, Yuki Oka - a neuroscientist at the California Institute of Technology in Pasadena - and her colleagues searched for water receptor cells. in the tongue of the mouse.

They used mutant mice, which in turn turned off some types of cells that contained taste receptors, then poured water into the mouth to see which cells would react.

Unexpectedly, the acid receptor receptors strongly reflected when mice drank water. In addition, when experimenting with mice to choose between water and artificial, odorless, colorless silicone oil, mice that lacked acidic receptors would take longer to select a glass containing water. This shows that these cells help distinguish water from other liquids.

Later, the team enjoyed the sour receptor cells to see if this would make mice want to drink water. They bred many mice to have light-sensitive proteins in their cells that contained their receptors that sensed sourness, causing them to act in response to laser light.

After training the mouse to drink water from a tap, the group replaced it with an optical tube that emits blue light. When mice 'drink' this blue light, they act as if they are drinking real water. Some even licked light about 2,000 times in 10 minutes to satisfy their thirst.

The mice did not know that the light was just a fake water, but they took longer than usual. This suggests a hypothesis that although taste receptors in the tongue can make people thirsty, it does not play a role in letting the brain know when to stop.

More research is needed to determine exactly how the receptor-containing cells can react to water and specifically what those mice feel when drinking water. But Yuki Oka guesses that water has pushed saliva - a mucus that is sour and salty - and changes the pH of sour cells making them easier to work on.

The results of this study were published in Nature Neuroscience.