Luminescence reporters have been used successfully in studies of circadian rhythms in many organisms. Ever since luciferase was introduced for real-time monitoring of gene expression rhythms in plants and cyanobacteria, luminescence reporter techniques have become a powerful tool for noninvasive assays of circadian oscillations. Using a real-time light detection system from cultured rodent tissues, we were able to record a circadian oscillation from the cultured suprachiasmatic nucleus (master pacemaker in the brain) for more than 16 month. We also discovered that most peripheral tissues were rhythmic in culture with distinct phases relative to the light dark cycle to which the animal had been exposed. Daytime restricted-feeding uncoupled the rhythms in digestive tissue from the environmental light cycle. Therefore the mammalian circadian system consists of at least two oscillatory systems; one is coupled with environmental light and another is coupled with food. This might have significant meaning for the adaptation of the circadian system to the natural environment. The study of multiple oscillatory systems also has had significant impact on medicine. We have begun to understand the circadian relationship between tumor cells and normal cells. Management of circadian rhythms may provide a new therapeutic approach for combating human disease. [J Physiol Sci. 2006;56 Suppl:S6]
