Scanning confocal fluorescence micrograph of a coronal section of the subfornical organ in the mouse brain, showing thirst neurons (yellow) and cell nuclei (magenta).
PHOTO: CHRISTOPHER ZIMMERMAN
We experience thirst every day, but where does this sensation come from? In the 1950s, Bengt Andersson proposed a tantalizing answer: Our brains might contain an “osmosensor” (1) that governs thirst, which consists of a group of cells that sense when we are dehydrated by directly monitoring the osmolarity of the blood. In a series of pioneering experiments , Andersson systematically infused salt into the brains of goats in an attempt to locate this osmosensor (2, 3). He ultimately discovered a small area within the hypothalamus where even minute amounts of salt triggered immediate, voracious drinking. Subsequent studies established that Andersson's osmosensor encompasses the subfornical organ (SFO), a brain region that is distinctively suited to detecting blood osmolarity because it lies outside the blood-brain barrier (4).
