Housing conditions influence the expression of food-anticipatory activity in mice

If food is presented for a limited duration once every 24 h, rats will gradually develop increased activity in the hours preceding mealtime, even if this is during a time of day when they are normally inactive. This food-anticipatory activity (FAA) is mediated by the entrainment of an endogenous self-sustaining circadian pacemaker. Mice are increasingly being used for the molecular analysis of behavior because of the large number of genetically manipulated mouse models available, but little is known about food entrainment in this species. This study assessed the impact of different housing conditions on the expression of FAA in a temporally restricted feeding paradigm. Wheel-running activity rhythms were recorded from mice (Mus musculus) undergoing food restriction while housed under one of two conditions. The results demonstrated that mice housed on open shelves showed robust FAA while those housed in isolation boxes did not. These results indicate that differences in susceptibility to food entrainment among mice (e.g., those with different genotypes) should be interpreted cautiously, since at least one strain is strongly affected by a relatively minor procedural difference that was not anticipated to have a significant impact. (C) 2004 Elsevier Inc. All rights reserved.