How does the body know when to stop drinking water?

This first drop of icy water after a scorching sun stroke can be deliciously appealing. A glbad of water after swallowing four others probably is not.

These varied reactions occur through the brain, which ensures that we do not drink too much or not enough water – two scenarios that would throw the body into a dangerous territory.

But how does the brain know when you encourage to stop or start drinking?

A new study conducted on mice suggests that a mysterious element of the intestine could play a role in predicting the amount of drink you need to satisfy your body. He then quickly informs the brain, which in turn decides his thirst, says a group of researchers today (March 26) in the journal Nature.

Thirst cells

In 2016, a group of researchers at the University of California at San Francisco (UCSF) discovered that when mice drink liquids, this causes the mouth and throat to send signals to the brain, which closes the brain cells that dictate thirst. These "thirst cells" are found in an area called the hypothalamus, which regulates thirst, blood pressure and other bodily processes, as well as in a small nearby place called the sub-cerebral organ. [10 Things We Learned About the Brain in 2018]

The mouth and throat begin to emit these signals after a few seconds after drinking something, although this usually takes about 10 minutes. at one o'clock for this water to actually enter the blood and be distributed to the thirsty cells of the whole body. The brain must find a balance – if it turns off the signals too quickly, you do not drink enough.

"In one way or another, the brain has a way to match these two time scales so that you can drink very quickly the right amount of water to meet your body's needs. "said the author of the study, Zachary Knight, badociate professor of physiology at UCSF and Howard. Researcher at the Hughes Medical Institute.

This is what the brain of the researchers sought to answer.

The elusive speaker

In the new study, Knight and his team implanted optic fibers and lentils near the mouse brain hypothalamus, which allowed them to monitor and measure the timing of thirst neurons. turn on and off. [13 Tips for Staying Hydrated in the Summer Heat]

When they administered salt water to the mice, the scientists found that thirst neurons stopped firing almost immediately, as expected. But a minute later, these neurons were reignited.

The throat and mouth-to-brain signals begin to quench thirst, regardless of the type of fluid. But since salty liquids can dehydrate the body, the "on" signal probably comes from elsewhere, after the throat and mouth have extinguished the neurons of thirst.

After having the impression that these neurons might receive the other signals from the intestine, the researchers directly infused water – salty and fresh – into the stomachs of the mice, thus avoiding the signals from the mouth and throat.

They discovered that fresh water also stopped the triggering of neurons, but not salty water. Moreover, when saltwater-impregnated mice received fresh water to drink, these thirsty neurons had, as expected, been extinguished – and then quickly re-ignited.

The findings suggest that there are molecules in the intestine that detect the salt content of liquids and use it to predict how much a drink will hydrate the body. This system, which only seemed to work when the mice were really dehydrated, sends this information to the brain in a minute and the neurons of thirst blink.

And sodium is not the only compound likely to trigger intestinal molecules, Knight told Live Science. "Anything that could change the osmolarity of the blood is detected by this system." (The osmolarity refers to the concentration of a liquid.)

The control of thirst

The results, if confirmed in humans, could benefit a large number of people.

For example, Knight noted that our ability to regulate thirst decreases with age. "So [elderly people] do not stay properly hydrated, which can lead to medical problems, especially during hot weather, for example, "he said.

The opposite may also be true: "A large proportion of marathoners tend to over-hydrate during a race," said Charles Bourque, a neuroscientist at McGill University in Canada, who was not part of the university. # 39; study. "The reasons for this are unclear, but a weakening of this signal from the gut to the brain could play a role."

In any case, the study "significantly advances knowledge on thirst control," Dr. Bourque told Live Science. And, as the findings are consistent with those obtained from brain tests in humans, at least some of the findings are likely applicable to humans, he added.

Although mice and humans obviously differ in some brain structures, their hypothalamis are very similar, Knight said.

The team also found that thirst signals were circulating along the main communication pathway between the brain and the intestines: the vagus nerve. When the researchers cut this nerve during a subsequent experiment, the thirsty neurons did not come back on when the mice started drinking.

Although they do not know for sure, the team thinks that the signals come specifically from the small intestine, which is the point most strongly related to the vagus nerve and which is also in the "good" period of the process digestive to activate. the thirst for nerves a minute after drinking water

For their next project, the team hopes to discover the origin of the signal.

Originally published on Science live.