For years, researchers have suspected that thirst is regulated by neurons in the subfornical organ (SFO) in the hypothalamus. But it has been difficult to pinpoint the exact neurons involved.

"When researchers used electrical current to stimulate different parts of the SFO of mice, they got confusing results," said lead author Yuki Oka, postdoctoral research scientist in the laboratory of professor Charles S. Zuker at Columbia University's Medical Centre in US.

The team hypothesized that there are at least two types of neurons in the SFO, including ones that drive thirst and others that suppress it."Those electrostimulation experiments were probably activating both types of neurons at once, so they were bound to get conflicting results," Oka added.

To test their hypothesis, the team turned to optogenetics, a more precise technique for controlling brain activity.With optogenetics, researchers can control specific sets of neurons in the brain after inserting light-activated molecules into them.

These "mind-control" experiments revealed two types of neurons in the SFO that control thirst: CAMKII neurons, which turn thirst on, and VGAT neurons, which turn it off.

The SFO is one of few neurological structures that is not blocked by the blood-brain barrier - it is completely exposed to the general circulation.

"This raises the possibility that it may be possible to develop drugs for conditions related to thirst," Oka said. The paper was published in the online edition of journal Nature.

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