Meal-related and rhythmic drinking: effects of abolition of rat's eating rhythm.

Eating and drinking in the rat, which are both highly rhythmic and nocturnal activities, are temporally and quantitatively associated. The present study abolished the rhythmicity of eating by temporally and quantitatively restricting food access to 12 equally sized bihourly meals daily (total food available was equal to 80% of daily ad libitum intake). Water access remained ad libitum and was monitored and quantified in terms of 1) nocturnality, 2) association with meals, and 3) changes in the association of food and water intake across the phases of the light-dark cycle. Similar parameters were obtained from the same rats with ad libitum access to both food and water. The results indicate that both rhythmic and meal-induced effects are detectable in the drinking of rats with restricted food access, although both the rhythmic and meal-associated factors are reduced compared with drinking under ad libitum food access. Most important, the data clearly demonstrate large changes in the association of food and water intake across the phases of the light-dark cycle. These findings indicate a complex interaction of meal-associated and rhythmic factors in the control of drinking.