A population of neurons that anticipate thirst and regulate fluid imbalances pre-emptively has been identified in the subfornical organ (SFO) of the brains of mice. The findings, reported in Nature this week, could help to explain why eating rapidly can make us thirsty and cold drinks feel especially thirst-quenching.
Thirst has been viewed as a stabilizing response to changes in blood volume or concentration, which motivates animals to drink in order to maintain fluid balance. However, most drinking behaviour is regulated too rapidly to be controlled by blood composition, and it has remained uncertain how homeostatic imbalances seem to be anticipated before they arise.
Zachary Knight and colleagues report an unexpected role for the SFO in the anticipatory regulation of thirst in mice that may shed light on this puzzle. They show that as well as monitoring the blood, neurons in the SFO are also modulated rapidly during eating and drinking by signals from the mouth that contain information about food and water consumption and temperature. This feedback is combined with blood composition information to allow the real-time ‘prediction’ of how ongoing food and water intake will alter fluid balance in the future, leading to adjustments in drinking behaviour.