To survive, we all need to satisfy our cravings for water. The benefits of doing so are many: water flushes the body of waste, cushions joints, helps deliver oxygen to cells, aids in digestion, and is required by the brain to function properly. Without water, basic physical processes begin to fail and we die in a matter of days.

Now, a team of scientists from Columbia University has identified two distinct set of neurons in the brain that control thirst: one set triggers the need to drink, and the other signals the body when to stop. The neurons reside in the subfornical organ (SFO) of the brain, according to findings published in Nature this week.

To determine the function of these neurons in the brains of mice, lead author Yuki Oka and colleagues used optogenetics to control specific sets of neurons. As the name suggests, optogenetics is a technology that combines genetics and optics to control cell function within the brain using light—in this case, by inserting molecules that are light-activated into specific SFO neurons. When a light is shined on these molecules with a laser, nerve impulses can be turned “on” or “off.”

The researchers found that activation of CAMKII neurons evoked thirst, while VGAT neurons suppressed it. “It’s a very elegant study using optogenetics to identify separate cell populations that clearly act in opposite ways on thirst,” said Joseph Verbalis of Georgetown University, who was not involved in the study.

CAMKII neurons are in red, VGAT neurons in green. Credit: Charles Zukar Lab.

The SFO is situated outside the blood-brain barrier and is only one of a few neurological structures that are exposed to bodily fluids. “These cells might then have the opportunity to directly sense electrolyte balance in body fluids," said Charles Zuker, one of the study's researchers, to HHMI News.

Further research may one day help individuals whose sense of thirst is weakened, such as the elderly who often become dehydrated. As Dr. Oka adds: The SFO's ideal position near the blood-brain barrier "raises the possibility that it may be possible to develop drugs for conditions related to thirst.”