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Sleep–Wake Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Margaret Kay-Stacey, Eunice Torres-Rivera, Phyllis C. Zee
The mammalian ‘master clock’ is located within the suprachiasmatic nucleus (SCN) in the anterior hypothalamus.12The SCN receives environmental and endogenous cues (or zeitgebers) to synchronize the endogenous rhythm with the external light–dark cycle and behavior. Zeitgebers include melatonin, physical and social activities, meal timing, and light.
Entrainment
Published in Sue Binkley, Biological Clocks, 2020
In considering a Zeitgeber, light in particular, we have to recognize that the signal itself has several parts—dark-to-light transition, lights-on, and light-to-dark transition. Pittendrigh36 discriminates between two possibilities: (1) a continuous action of light, and (2) light being an effective signal only as it goes on and off. Both could in fact be operating.
Endocrine Functions of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
Living organisms have an internal clock that helps the body adapt to the external environment. Throughout the 24-h day, the clock regulates many physiological, endocrine, and mental processes, including sleep, body temperature, metabolism, blood pressure, hormone release and alertness. Circadian rhythms are endogenously generated ~24-h biological rhythms that are organized in two levels: a molecular level represented by the clock genes, and a systemic regulatory level represented by the neuroendocrine networks. The circadian oscillation is synchronized by external environmental cycles, primarily the light/dark cycle of the geophysical day and night. External rhythmic events that can synchronize biological rhythms are called zeitgebers or synchronizers. “Entrainment” is defined as a synchronization between oscillators with different but similar periods that occurs when one of the oscillators imposes its period on the other.
Zeitgebers and their association with rest-activity patterns
Published in Chronobiology International, 2019
Mirja Quante, Sara Mariani, Jia Weng, Catherine R Marinac, Emily R Kaplan, Michael Rueschman, Jonathan A Mitchell, Peter James, J. Aaron Hipp, Elizabeth M Cespedes Feliciano, Rui Wang, Susan Redline
“Zeitgebers” refer to environmental and social cues that provide input to the circadian system and help to synchronize biological rhythms (Aschoff et al. 1975). While light is the chief environmental cue (Pittendrigh 1964), non-photic stimuli, such as food intake and physical activity, can also influence circadian rhythms (Mistlberger and Skene 2004, 2005). The importance of food exposure as a zeitgeber is supported by both animal and human experimental research (Stokkan et al. 2001; Wehrens et al. 2017). For example, a rodent study demonstrated that the central biological clock in the suprachiasmatic nucleus can be entrained by diurnal cyclic exposure to food (Castillo et al. 2004; Mendoza et al. 2005). In humans, a laboratory-based study of 32 healthy women demonstrated that changes in meal timing affected circadian-related parameters such as temperature and cortisol, as well as glucose tolerance (Bandin et al. 2015). The role of exercise as a zeitgeber is also supported by experimental research. Exercise or physical activity has different physiological effects according to its timing. Specifically, a laboratory study showed that evening, but not morning, exercise delayed the circadian rhythm by about 1 hour (as indicated by the rising phase of plasma melatonin) (Yamanaka et al. 2015).
Voluntary exercise stabilizes photic entrainment of djungarian hamsters (Phodopus sungorus) with a delayed activity onset
Published in Chronobiology International, 2018
D. Weinert, K. Schöttner, A.C. Meinecke, J. Hauer
Circadian rhythms are generated by an endogenous clock that harbors in the suprachiasmatic nuclei (SCN) in mammals (Dibner et al. 2010; Weaver 1998). As the period length (tau) deviates from the 24-h cycle of the environment, the rhythm has to be synchronized by external cues, so-called zeitgebers (Aschoff 1960). The main zeitgeber for animals and humans is the daily light-dark cycle, though other environmental cues may be important as well (Sharma and Chandrashekaran 2005). Entrainment is achieved by resetting mechanisms, which correct tau and establish a stable phase relationship (phase angle) between the endogenous circadian pacemaker and the external stimulus (Johnson et al. 2003). Particularly, with respect to photic zeitgebers, two models have been developed (Daan 2000), which can be briefly described as follows. Aschoff’s parametric model postulates that light and dark speed up and slow down, respectively, circadian rhythms in diurnal species, the opposite effects taking place in nocturnal animals. Pittendrigh developed the non-parametric model, which postulates that the light-dark and dark-light transitions cause phase changes thereby entraining the circadian rhythms.
Prospects for circadian treatment of mood disorders
Published in Annals of Medicine, 2018
Anisja Hühne, David K. Welsh, Dominic Landgraf
The timing of sleep and wakefulness is largely controlled by circadian clocks, but sleep and wakefulness also directly or indirectly alter circadian rhythms. Indeed, sleep can act as a Zeitgeber for circadian rhythms. Depending on the time of day, naps can cause phase advances or phase delays of melatonin and other hormone rhythms [98–100]. Whether these effects are mediated directly by sleep or indirectly by reduction of light, activity, social contacts, or changes of posture during naps is not clear [100]. Insufficient sleep also alters the temporal organization of the human blood transcriptome, reducing circadian rhythm amplitude [101].