Subfornical Organ in Hypothalamus is a Dedicated Brain System for Thirst

Neuroscientists from Columbia University Medical Center have identified the 'switch' or neurons in brain, that are responsible for switching thirst on or off.

Researchers 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. Lead author Dr. Yuki Oka, said, "Those electrostimulation experiments were probably activating both types of neurons at once, so they were bound to get conflicting results." 

To test their hypothesis, researchers turned to optogenetics, a more precise technique for controlling brain activity. Optogenetics helps researchers 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 in the vicinity. 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 researchers turned on CAMK11 neurons, mice immediately began to seek water and to drink intensively. This behavior was equally strong in well-hydrated mice and in dehydrated mice. 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, and the 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 turn off thirst. When the researchers turned on these neurons with light, dehydrated mice immediately stopped drinking water, even if they were drinking water. Dr. Oka said, "Together, these findings show that the SFO is a dedicated brain system for thirst." 

Source:The paper has been published in the online edition of Nature.