Cradle of thirst in the brain identified

In a new study, scientists have identified the 'switch' or neurons in brain, that's responsible for switching thirst on or off.

A team of neuroscientists from Columbia University Medical Center hypothesized that there are at least two types of neurons in the subfornical organ (SFO), in the hypothalamus 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," said lead author Yuki Oka, PhD.

To test their hypothesis, Drs. Oka and Charles S. Zuker 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. Shining light onto these molecules turns on the neurons without affecting other types of neurons nearby.

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.

When the researchers turned on CAMK11 neurons, mice immediately began to seek water and to drink intensively. This behavior was as strong in well-hydrated mice as in dehydrated ones. Once the neurons were shut off-by turning off the light-the mice immediately stopped drinking.

They also found that light-stimulation of the CAMKII neurons did not induce feeding behavior. In addition, light-induced thirst was specific for water and did not increase the animals' consumption of other fluids, including glycerol and honey.

Similar experiments with VGAT neurons showed that these neurons act to turn off thirst.

When the researchers turned on these neurons with light, dehydrated mice immediately stopped drinking, even if they were drinking water. "Together, these findings show that the SFO is a dedicated brain system for thirst," said Dr. Oka.

The paper is published in the online edition of Nature.