The sensory psychobiology of thirst and salt appetite.

Thirst and the hunger for sodium containing fluids and food (i.e., sodium appetite) are the consequences of the generation of unique central nervous system states. Altered body fluid homeostasis produces sensory and perceptional changes that arise from signals generated in the body that serve as indices of body fluid balance and distribution. These signaling mechanisms activate networks of brain neurons that use specific neurochemicals to communicate between cells and process information. The brain integrates information derived from various bodily sources so that thirst and sodium appetite are in a true sense the synthetic products of the nervous system. In recent years much has been learned about the stimuli and receptor systems involved in signaling the brain to reflect the status of bodily fluids and about the central neural substrates that process such inputs to generate thirst and sodium appetite. Knowledge about the sensory nature of thirst and sodium appetite provides a basis for understanding the biological constraints under which thirst and sodium appetite operate. This information is important for appreciating the extent to which thirst and sodium appetite motivational states and behaviors can be relied on to maintain and repair disruptions of body fluid homeostasis.