Light-dark cycle modulates drinking to homeostatic challenges.

Both homeostatic and rhythmic variables are empirically and theoretically important controls of behavior. Yet, drinking behavior has been studied largely from one point of view or the other. The present study examined both homeostatic and rhythmic variables and found evidence for an important interaction of these two types of control of drinking behavior. The drinking rhythm of rats on a light-dark cycle was established. Water intake after cellular- or extracellular-related challenges was then measured both at a time of a peak and at a time of a trough of the drinking rhythm. The results indicate that rats drink more water after challenges in their early active phase than in their early inactive phase. The results demonstrate that rhythmic variables modulate the homeostatic controls of drinking behavior. The importance of the interaction of homeostatic and rhythmic variables in models of integrative control of behavior is discussed.