Thirst is controlled by a section of brain identified by a team of medical researchers.

Howard Hughes Medical Institute investigators discovered how thirst is regulated by a subset of cells within the brain, known as the subfornical organ (SFO). When this region was stimulated in laboratory mice, the rodents immediately started drinking water, even if the animals were already well-hydrated.

"We view the SFO as a dedicated circuit that has two elements that likely interact with each other to maintain the perfect balance, so you drink when you have to and you don't drink when you don't need to," Charles Zuker from Columbia University said.

A second set of cells controls the urge to cease drinking, Zuker and his team were able to determine. The investigators placed a light-sensitive protein into the SFO region in the brains of mice. This provided the researchers with the ability to stimulate the area with light from a blue laser. Researchers found that the test animals would keep drinking water for as long as the light kept shining. The tiny creatures drank up to eight percent of their body weight in water. This is the human equivalent of drinking 1.5 gallons of water in just 15 minutes. However, the creatures were not interested in drinks other than water, the study found.

Thirst control in animals helps to balance electrolyte levels, and maintain proper pressure within cells. Zuker's team previously identified taste receptors within brains that control the five basic tastes of salt, sweet, sour, bitter, and umami. The neural mechanism controlling desire for salt causes cravings for the substance when levels are low, but not when there is enough salt in the body. This process, along with the regions controlling thirst, helps to control electrolyte levels.  

"This is how the taste system regulates salt intake, which is very important for salt homeostasis in the body. But this is just one side of the coin. Salt intake has to be balanced by water intake," Yuki Oka, a postdoctoral fellow researcher, told the press.

Previous research stimulating the SFO and other circumventricular organs in the brains of laboratory mice resulted in indefinite results.

Stimulation of the cells responsible for the suppression of thirst did not alter the desire of the animals to eat food or consume salt. This finding suggests the region is involved solely in the regulation of water intake.  

Future research will examine if similar regions in the human brain carry out the same function.

Investigation of the role of the subfornical organ in controlling thirst was published in the journal Nature.

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