Duez H, Staels B. Rev-erb: an integrator of circadian rhythms and metabolism. J Appl Physiol 107: 1972–1980, 2009. First published August 20, 2009; doi:10.1152/japplphysiol.00570.2009.—The endogenous circadian clock ensures daily rhythms in diverse behavioral and physiological processes, including locomotor activity and sleep/wake cycles, but also food intake patterns. Circadian rhythms are gen...

PURPOSE OF REVIEW There is growing awareness of the importance of circadian rhythmicity in various research fields. Exciting developments are ongoing in the field of circadian neurobiology linked to sleep, food intake, and memory. With the current knowledge of critical 'clock genes' (genes found to be involved in the generation of circadian rhythms) and novel techniques for imaging cyclic event...

Cyanobacteria are the only bacterial species found to have a circadian clock. We used DNA microarrays to examine circadian expression patterns in the cyanobacterium Synechocystis sp. strain PCC 6803. Our analysis identified 54 (2%) and 237 (9%) genes that exhibited circadian rhythms under stringent and relaxed filtering conditions, respectively. The expression of most cycling genes peaked aroun...

The circadian clock is a cellular time-keeper mechanism that regulates biological rhythms with a period of ~24 h. The circadian rhythms in metabolism, physiology, and development are synchronized by environmental cues such as light and temperature. In plants, proper matching of the internal circadian time with the external environment confers fitness advantages on plant survival and propagation...

Dijk, Derk-Jan, and Steven W. Lockley. Invited Review: Integration of human sleep-wake regulation and circadian rhythmicity. J Appl Physiol 92: 852–862, 2002; 10.1152/japplphysiol.00924.2001.—The human sleep-wake cycle is generated by a circadian process, originating from the suprachiasmatic nuclei, in interaction with a separate oscillatory process: the sleep homeostat. The sleep-wake cycle is...

In zebrafish, the expression of long-wavelength cone (LC) opsin mRNA fluctuated rhythmically between the day and night. In a 24-h period, expression was high in the afternoon and low in the early morning. This pattern of fluctuation persisted in zebrafish that were kept in constant darkness, suggesting an involvement of circadian clocks. Functional expression of Clock, a circadian clock gene th...

Disturbances in circadian rhythms have been suggested as a possible cause of bipolar disorder (BD). Included in this study were 31 mood episodes of 26 BD patients, and 18 controls. Circadian rhythms of BD were evaluated at admission, at 2-week intervals during hospitalization, and at discharge. All participants wore wrist actigraphs during the studies. Saliva and buccal cells were obtained at 8...

Successful adaptation to modern civilization requires the internal circadian clock to make large phase shifts in response to circumstances (e.g., jet travel and shift work) that were not encountered during most of our evolution. We found that the magnitude and direction of the circadian clock's phase shift after the light/dark and sleep/wake/meal schedule was phase-advanced (made earlier) by 9 ...

Circadian rhythms, or biological day-to-day rhythms, are stimulated and regulated by different factors within and outside the body. These circadian rhythms are controlled by a specialized set of pacemaker cells in an area of the brain called the Suprachiasmatic Nucleus (SCN). If the circadian pacemaker is functioning properly, these cells will exhibit neuronal firing that will peak around mid-d...

Most of the biological functions, including the immune system, are linked to circadian rhythms in living organisms. Changes occurring to biological parameters as the result of these circadian rhythms can therefore affect the outcome of a disease. For decades, model organisms have proven to be a great tool to understanding biological mechanisms such as circadian cycle and immunity. In this revie...