Scientists Show How the Brain May Be Wired for Drinking Fluids
Scientists have uncovered a high-resolution map of the wiring inside the mouse brain’s thirst center. With these blueprints, they could trick mice into becoming light or heavy water drinkers. Moreover, they discovered a quenching circuit that knew when to tell the brain, “Stop, the body has had enough.”
Supported, in part, by NIH’s BRAIN Initiative, the results may also provide a glimpse into the rules that govern how the brain’s circuits work.
“Bodily fluids are maintained by a delicate and tightly regulated balance of thirst and satiety,” said Dr. Yuki Oka of the California Institute of Technology, senior author of the study published in Nature. “We genetically mapped out the neuronal circuits that tell the body when to drink.”
His group studied the circuits of the lamina terminalis, the thirst center located deep inside the brain. For decades, scientists have known that three groups of neurons in this area cooperated to control drinking, and they even had clues as to which type of neurons did so. But no one had a genetically defined circuit diagram for how they did it. Nor did they completely understand how the cells tell the body to stop drinking well before the stomach fully absorbs water and other fluids.
Using genes designed to help scientists dissect brain circuits, the researchers found that opposing lines of communication running through an area of the lamina terminalis called the median preoptic nucleus may be critical players. One line was essentially responsible for telling the mice to drink while the other line told them when to stop. Both seemed to work in sequential order, relaying drinking or quenching messages from one neuron to another.
“Our results shed light on a new aspect of appetite regulation,” said Oka. “It appears that the act of drinking itself sends satiety signals to the brain and these neurons act like fluid flow-meters that tell the brain when the body has had enough to drink. This circuit may be the reason why the brain knows to stop drinking well before the gut has fully absorbed all the water the animal drinks.