Researchers partially funded by NHLBI have discovered that a reaction in the gut informs the brain that it should switch the neurons that indicate thirst on or off. The findings, published in the journal Nature, reveal how the gastrointestinal tract measures the salt concentration in the intestines and relays this info directly to the brain.
The team of researchers had wondered how the brain knows exactly how hydrating a drink will be, since sea water doesn't quench thirst but activates many of the same receptors in the mouth and throat as ice water from the fridge.
They tracked neural activity in living mice and watched in real time as these the brain and the gut communicated about thirst.
Using flexible optical fibers implanted near the hypothalamus they watched the activity of thirst neurons as mice drank salty water. These neurons did go quiet as soon as the thirsty animals took a drink, but then quickly switched back on, as if some other sensor were testing the water the animal had just drunk and alerting the brain that it should stay thirsty.