A review of the history and pioneers in the study of thirst and drinking is provided, including the debate between dry mouth and systemic theories. The measurement of thirst and drinking is discussed, including whether water has a taste. Consideration is given of the three main phases of components of drinking, namely, its initiation, maintenance, and termination. The chapter ends with the study of brain mechanisms, and in particular the pivotal role of structures of the lamina terminalis.

Cellular dehydration caused by stimuli such as hypertonic NaCl or mannitol cause a sustained shrinkage of osmosensitive cells, and in osmosensitive neurons this is transduced into a proportional change in firing rate. The basal firing rate of these neurons may encode an effective set point for osmoregulation. In the brain, these osmoreceptors seem to be predominantly in the SFO, MnPO, and OVLT. From selective lesion and other evidence, it appears that these regions act in a synergistic manner, such that optimal drinking and/or AVP secretion occurs when all three of these interconnected regions are functional. Some data suggest that there may be species differences in the details of this integrated functioning of the lamina terminalis.