Circadian rhythms refer to oscillations in biological processes with a period of approximately 24 h. In addition to the sleep/wake cycle, there are circadian rhythms in metabolism, body temperature, hormone output, organ function and gene expression. There is also evidence of circadian rhythms in synaptic plasticity, in some cases driven by a master central clock and in other cases by periphera...

Under field conditions, a vast majority of the behavioural and physiological properties of an organism show rhythmic variation with a daily repetition. Although some of these rhythms may be passive systems, driven by the external environment, an increasing body of evidence indicates that, instead, most of the daily rhythms appear to be endogenous, and are merely synchronized by the environment....

BACKGROUND The loss of diurnal rhythm in blood pressure (BP) is an important predictor of end-organ damage in hypertensive and diabetic patients. Recent evidence has suggested that two major physiological circadian rhythms, the metabolic and cardiovascular rhythms, are subject to regulation by overlapping molecular pathways, indicating that dysregulation of metabolic cycles could desynchronize ...

The temporal order of physiology and behavior in mammals is primarily regulated by the circadian pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN). Taking advantage of bioluminescence reporters, we monitored the circadian rhythms of the expression of clock genes Per1 and Bmal1 in the SCN of freely moving mice and found that the rate of phase shifts induced by a single light pu...

Ultradian rhythms in blood pressure (BP) are known to exist, but their modification in hypertension is largely unknown. The present study was undertaken to assess the integrity of ultradian and 24-hour BP rhythms in dipper (n=100) and nondipper (n=20) hypertensive patients compared with 44 dipper normotensive individuals. Fourier analysis was used to fit ultradian (12, 8, and 6 hour) and 24-hou...

In mammals, circadian rhythms in behavior and physiology are controlled by a central pacemaker, the SCN, and subordinated clocks throughout the body. On the molecular level, these clocks are based on transcriptional/translational feedback loops involving a set of clock genes that regulate their own transcription. Among the components driving the mammalian circadian clock are the Period 1 and 2 ...

Introduction: Circadian rhythms are genetically programmed traits coordinating behavior and metabolic responses with daily repeating environmental challenges, primarily with the solar day. Aging and circadian rhythms are interrelated: aging can modify the circadian rhythms, whereas age-changes of the rhythms contribute to the declined adaptability in aging. Material and Methods: Circadian rhyth...

The suprachiasmatic nucleus (SCN) is the major circadian pacemaker in mammals. When fetal tissue containing the SCN is transplanted into young rats whose circadian rhythms have been abolished by SCN lesions, the rhythms gradually reappear. Circadian rhythms in many rats deteriorate or disappear with age. The rationale of the present study was that old rats with poor circadian rhythms resemble y...

The human circadian system has been considered as controlled by two — or even more — oscillators which are represented by the sleep-wake cycle and the rhythm of rectal temperature (Wever 1975). Both rhythms are influenced by environmental time cues but also affect each other mutually. The interaction between the two rhythms is especially obvious in the absence of external stimuli, i.e., under c...

BACKGROUND Animals, including humans, exhibit a variety of biological rhythms. This article describes a method for the detection and simultaneous comparison of multiple nycthemeral rhythms. METHODS A statistical method for detecting periodic patterns in time-related data via harmonic regression is described. The method is particularly capable of detecting nycthemeral rhythms in medical data. ...