Few pleasures compare to a long cold glass of water on a hot day. When a glass of water or other delicious drink makes its way to your digestive tract, your brain tracks it — but how? Scientists have known for a long time that thirst is controlled by neurons that send an alert to put down your glass when you’ve had enough. What exactly tells them that the time has come, however, remains a bit of a mystery.
In an earlier study, a team of researchers found that the act of swallowing a liquid – really anything from water to oil – is enough to induce temporary thirst. But they know that swallowing isn’t the only source of satisfaction. There are signals to quench thirst from deep within the body.
In one The paper was published Wednesday in the journal NatureScientists from the same lab report that they tracked signals down the neck, through one of the body’s most important nerves, into the intestines, and eventually to an unexpected place for growth. This triggers: a collection of small veins in the liver.
The swallowing motion can provide a quick way for the body to keep track of fluid intake. But whatever you swallow will quickly reach your stomach and intestines, and then its identity will become clear to your body as to whether or not something can meet your body’s hydration needs. Water changes the concentration of nutrients in your blood, and researchers believe this is what leads to true satiety.
“There’s a mechanism to make sure that what you’re drinking is water and not anything else,” said Yuki Oka, a professor at Caltech and author of both studies. To find out where the body senses changes in your blood levels, Dr. Oka and his colleagues first put water in the intestines of mice and monitored the activity of the nerves that connect the brain to the brain. intestinal tract, which is thought to act similarly in humans. . A major nerve, the vagus nerve, is active closest to the time when water reaches the gut, suggesting that this is the route through which information reaches the brain.
The researchers then went one by one and cut each nerve’s connection to different regions in the gut. To their surprise, nothing changed when they cut off contact with their guts.
Instead, the liver’s portal veins – the vessels that carry blood from around the intestines to the filter – have the function of isolating and silencing messages going back to the brain.
These veins transport nutrients and fluids into the liver, so it makes sense that they could be a hub for monitoring thirst, says Dr. Oka. However, the team found that just letting water flow through the portal veins was not enough to get the nerve to work. Something about the appearance of water had to activate another part of the body’s Rube Goldberg hydration machine.
The researchers narrowed it down to a hormone called intestinal-active peptide, or VIP. As water reaches the portal veins, VIP levels rise and it is the VIP, not the water itself, that causes vagal activation, alerting the brain.
The fascinating thing is, scientists don’t know how water is causing this increase. They hope to continue monitoring the signals and pinpointing which cells and molecules connect these simple veins and the large acronym peptide.
“That’s the main problem we can tackle next,” said Dr. Oka.
And perhaps there is much more to learn. Although VIP caused the vagus nerve to mute, the signal was not as strong as the researchers would have expected if it were acting alone. Water is so important to the body’s functioning that Dr Oka and his team think our brains most likely have redundant ways of keeping track of it. With every cup of water you drink, you’re putting that system through its paces.
https://www.nytimes.com/2022/01/26/science/thirst-brain-neurons.html Your body thirst messenger is in an unexpected place