The neurobiology of thirst and salt appetite

The first act of life was the capture of water within a cell membrane,¹ and maintaining fluid homeostasis is critical for the survival of most organisms. In this review, we discuss the neural mechanisms that drive animals to seek out and consume water and salt. We discuss the cellular and molecular mechanisms for sensing imbalances in blood osmolality, volume, and sodium content; how this information is integrated in the brain to produce thirst and salt appetite; and how these motivational drives are rapidly quenched by the ingestion of water and salt. We also highlight some of the gaps in our current understanding of the fluid homeostasis system, including the molecular identity of the key sensors that detect many fluid imbalances, as well as the mechanisms that control drinking in the absence of physiologic deficit, such as during meals.