The control of drinking.

Thirst is a sensation normally aroused by a lack of water and associated with a desire to drink water. The mechanisms involved in the control of drinking are useful to study, not only because of their clinical relevance, but also because the stimuli that lead to drinking can be identified, measured and manipulated, so allowing the basis of a relatively complex, motivated behaviour to be analysed. Body water is contained within two main compartments. The intracellular water accounts for approximately 40% of body weight, and the extracellular water is approximately 20% of body weight, divided between the blood plasma, 5% of body weight and the interstitial fluid, 15% of body weight. After water deprivation, significant depletions of both the cellular and extracellular fluid compartments are found. To discover whether changes in either or both fluid compartments can act as stimuli for drinking, effects of selective depletion of one of the compartments on drinking, and the mechanisms activated, have been investigated as described below.