Classical thirst stimuli can be modified by other ongoing physiologic conditions. In addition, although food intake and water drinking are traditionally seen as contemporaneous behaviors, stimuli for food intake can be separated from water drinking and vice versa. In this chapter, we address two issues: independence of the two behaviors and the impact of non-thirst–related stimuli on water drinking behaviors.
Do all stimuli for food intake induce concomitant water drinking? Although pattern analysis of ad libitum food and water consumption definitively demonstrated the coordination of those two behaviors (de Castro 1988; Fitzsimons and LeMagnen 1969; Kissileff 1969), it is clear that water drinking can occur under physiologic conditions in the absence of food intake (Zorilla et al. 2005), and even under conditions of water restriction some food intake does occur (Fitzsimons and LeMagnen 1969; Zorilla et al. 2005). However, a more physiologic approach to the concordance of the two behaviors is the examination of the intervals of water drinking during 24 h, ad libitum periods, and under these conditions, significant amounts of water are consumed independent of food intake (Zorilla et al. 2005). This may seem obvious when one considers the importance of osmotic and volemic stimuli for drinking; however, when one considers water drinking in the presence of food intake, a certain necessity for the coincident behaviors overrides their independence. This is in no small part due to the lubricative function of fluid taken with solid food, and the resulting osmotic stimuli following solute absorption in the stomach and intestines. But do all stimuli for food intake also stimulate drinking? Evidence from the Daniels laboratory (Mietlicki et al. 2009) provides a clear, negative answer.
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