[Circadian regulation of sleep-wake cycles and food anticipation]

The circadian clock is crucial for efficient physiological function and drives the temporal regulation of the sleep-wake state, metabolism, and behavior. The timing of food intake and the accompanying behavior are both controlled by the internal clock, which is located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The SCN is considered as the master clock because the circadian rhythms for most physiological and behavioral processes are terminated after SCN ablation. The molecular framework of circadian oscillations can be best studied in the SCN. A "core" set of circadian clock genes form autoregulatory transcription-translation feedback loops that are believed to drive daily rhythms in individual cells. These clock genes are expressed in a circadian manner not only in the SCN but also in other parts of the brain and many peripheral tissues. Mammals can anticipate a predictable daily mealtime through entrainment of circadian oscillators. Because the restriction of food availability to a specific time of the day elicits anticipatory behavior even after ablation of the SCN, such behaviour is assumed to be controlled by another circadian oscillator. In this paper, we have (1) reviewed studies involving the identification of the circadian clock and (2) aimed to elucidate the complex mechanism underlying feeding-associated rhythms by achieving a deep understanding of the circadian phenotypes of the SCN.