It seems simple enough: an animal feels thirsty, it drinks some water, it stops feeling thirsty. Though this unremarkable sequence of events is probably familiar to any of the billions upon billions of animals that populate the Earth, scientists are only now closing in on the neural circuitry that translates a lack of water in the body into the inescapable urge to drink.
The part of the brain that senses and regulates the body’s internal water balance is called the lamina terminalis. It has three connected subregions – the subfornical organ (SFO), the organum vasculosum lamina terminalis (OVLT) and the median preoptic nucleus (MnPO).
Recent research in mice has shown that dehydration triggers activity in the SFO, which then activates the MnPO, which in turn appears to instigate drinking behaviour. When the body’s fluid levels return to normal, the MnPO sends a signal back to the SFO that makes the thirst disappear. By stimulating and deactivating certain neurons in these parts of the brain, researchers confirmed the link.
The image above shows excited neurons in the MnPO in response to dehydration.