Physiology & Behavior, Vol. 25, pp. 279-281. Pergamon Press and Brain Research Publ., 1980. Printed in the U.S.A. Dissociation of Circadian Rhythms for Food and Water Consumption in Mice I B. POSSIDENTE, J. P. HEGMANN, B. ELDER AND L. CARLSON Interdepartmental Program in Genetics and Department of Zoology, University of Iowa, Iowa City, IA 52242 Received 9 April 1980 POSSIDENTE, B., J. P. HEGMANN, B. ELDER AND L. CARLSON. Dissociation of circadian rhythmsfor food and water consumption in mice. PHYSIOL. BEHAV. 25(2) 279--281, 1980.--Under constant light, a circadian rhythm in food consumption persisted in animals deprived of water, and a circadian rhythm in water consumption persisted in the absence of food. This observation demonstrates that each of these circadian rhythms can be driven by a biological clock mechanism independently of the other. Even though absolute levels of food and water consumption under constant light were heavily interdependent, the rhythmicity of each behavior did not change significantly in the absence of the other behavior. This result shows separate control of absolute level of performance and timing of these circadian behaviors. Circadian rhythm Food consumption Water consumption Mus musculus INDIVIDUAL organisms display many different circadian rhythms at the same time. The organization of the biological clock mechanism underlying these rhythms may be as simple as a single circadian clock driving all rhythms in common, or as complex as many clocks driving different rhythms inter- dependently [3]. One way to begin approaching the problem of understanding circadian organization, is to identify ob- servable rhythms which are directly coupled to a biological clock, as distinct from rhythms which are a secondary con- sequence of other rhythms. We have shown previously that food and water consump- tion in mice display true circadian rhythms (i.e., they persist under constant environmental conditions) [6]. In these mice peak water consumption follows peak food consumption in time, suggesting that the rhythm in water consumption might be a consequence of the rhythm in food consumption. That is, periodic intense food consumption might induce a "phy- siological debt" leading to regular bouts of drinking. In terms of the biological clock mechanism driving these rhythms, this interpretation would be functionally and phys- iologically equivalent to considering a rhythm for water con- sumption "coupled" to the food consumption rhythm. Oat- ley [4] has shown with rats, that the periodicity in drinking is independent of the periodicity in eating, and persists even in the total absence of food consumption. But Oatley's obser- vations were made under a light-dark cycle, and technically it must be recognized that the observed rhythmicity might have been related to photoperiodic time cues rather than an internal biological clock mechanism. In addition, the physi- ological mechanisms regulating food and water consumption are complex, and even though most water consumption fol- lows food consumption, it's not clear that the reciprocal hy- pothesis can be rejected: that a circadian rhythmicity in food consumption is dependent on a rhythmicity in water con- sumption. In view of these considerations, and the fact that Pittendrigh and Daan [5] have demonstrated many differ- ences in biological clock function across four species of ro- dents, we investigated the interdependence of circadian rhythms for food and water consumption in mice under con- ditions of constant light. Here we show that a circadian rhythm in water consumption continues under constant light in the absence of food consumption, and a circadian rhythm in food consumption continues in constant light in animals deprived of water. The phase and amplitude of each rhythm remains unaffected by the absence of the other behavior and the large changes in amounts of food and water consumed as a result of the experimental treatments. METHOD Subjects were 39 male mice from a genetically heteroge- neous stock of Mus rnusculus [1]. All were raised under a 16:8 LD photoperiod and ranged in age from 40--60 days at the start of the experiment. During the experiment the mice were housed individually in 20x12x10 cm stainless-steel cages with approximately 500 ml of crushed corncob bed- ding. Ambient temperature was maintained at 22 ° - 1 °. Food and water consumption were measured by weighing food (Teklad 6% mouse diet blocks) and water bottles (15 ml plastic bottles with stainless-steel ball-bearing sipper tubes) to the nearest 0.1 g at two-hour intervals. Food and water were provided ad lib. All mice were measured for food and water consumption under a 16:8 LD cycle for 2 days to gather baseline data. Subsequently constant light, ranging in intensity from 30-400 lux in different parts of the room, was imposed on the mice. Cages were arranged in blocks by treatment group so that different light intensities were experienced equally by each 1The first author was supported by a NIH pre-doctoral traineeship in Genetics. The authors thank Cindy Stiffen, Jane Kotecki and Debra Recher for assistance in collecting data, and John Kirk for technical assistance. Copyright © 1980 Brain Research Publications Inc.--0031-9384/80/080279-03502.00/0