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Resetting
Published in Sue Binkley, Biological Clocks, 2020
When scientists methodically exposed organisms to single perturbing signals (e.g. light pulses) at different times over 24 hours, the phase shifts they obtained were not all the same. They graphed the direction and amount of phase shift obtained versus the time that the pulse was given. Such a graph is called a phase response curve or PRC.
Methodologies for Determining Rhythmic Expression of Seizures
Published in Steven L. Peterson, Timothy E. Albertson, Neuropharmacology Methods in Epilepsy Research, 2019
Phase shifts are determined by placing a subject in constant conditions (constant darkness, variable feed, water and cage changes; no synchronizing cues) and then exposing the individual to a small duration of an entraining stimulus (usually a short pulse [15 min] of light) at different times throughout the circadian cycle. The individual will either advance, delay, or not shift the rhythm of interest, depending on the time that the stimulus is presented. A curve of responsiveness (phase response curve) can be constructed with the period of the cycle on the abscissa and phase advances plotted in the positive direction of the ordinate and phase delays plotted in the negative direction of the ordinate (Figure 12.4).23 This curve indicates when the stimulus is most and least effective at shifting the rhythm of interest and provides information about the function of the circadian clock. Researchers interested in rhythms use phase response curves to predict when and how specific stimuli will alter circadian clock function.
The Pineal Gland Energy Transducer
Published in Len Wisneski, The Scientific Basis of Integrative Health, 2017
A “reset” of the phase-response curve or a “phase shift” occurs when an environmental factor (e.g., travel) or an exogenous substance (e.g., β-adrenergic blocking agents or melatonin) changes the time of melatonin secretion. A delayed response or phase shift takes place when the secretion of melatonin shifts to a later time, which could occur from exposure to bright light at night or β-adrenergic blocking agents. An advanced response or phase shift occurs when there is exposure to bright light in the latter part of the night or very early morning hours. This results in a phase shift that causes melatonin to secrete earlier in the night.
Stuart Maxwell Armstrong (1947-2022)
Published in Chronobiology International, 2022
I first met Stuart in 1984 at a CIBA Foundation Symposium on Photoperiodism, Melatonin and the Pineal Gland (published in 1985), initiated by Professor Vincent Marks and myself, in fact I think I invited him. Here he and Jenny reported what may be more important from the point of view of pineal physiology – that pinealectomy i.e. removal of circulating melatonin, facilitates phase shifting in rats. Thus the endogenous role of melatonin apart from signalling day length may well be to counter undesirable shifts in circadian phase. The circadian time dependency of melatonin’s effects, and thus the melatonin phase response curve (PRC) together with possible dose-dependency were all addressed in these studies. Working with Cassone and Chesworth, Stuart was also to show the SCN dependency of melatonin’s chronobiotic effects. Early work in humans was also presented at this CIBA Symposium and both rats and humans heralded an enormous expansion of interest in the therapeutic potential of melatonin including in our work on entrainment of the blind (BMJ, 1986; Lancet, 1988; J. Endocrinology, 2000).
Per1 mutation enhances masking responses in mice
Published in Chronobiology International, 2022
Nemanja Milićević, Arthur A. Bergen, Marie-Paule Felder-Schmittbuhl
An alternative explanation is that Per1 inhibits masking responses by a pathway in the brain. This possibility is supported by studies on the effects of Per genes in entrainment. For example, Per1−/− mice show a greater phase response curve (PRC) amplitude compared to WT mice, whereas Per2−/− mice were not significantly different compared to WT mice (Pendergast et al. 2010). Others have found that Per1 mutant mice cannot advance the phase of the clock in response to a nocturnal light pulse at ZT22, whereas Per2 mutant mice cannot delay the phase of the clock in response to a light pulse at ZT14 (Albrecht, Albrecht et al. 2001). Yan and Silver reported differential localization of Per1 and Per2 mRNA expression in the SCN upon light pulses that entrain the clock (Yan and Silver 2002). In the SCN shell, they found that a phase advancing light pulse increased Per1, but not Per2 mRNA expression. In contrast, they found that Per2, but not Per1 mRNA, was increased in the SCN shell after a phase delaying light pulse (Yan and Silver 2002). Because there is an intertwined relationship between masking and entrainment (Shuboni et al. 2012), it is tempting to speculate that there is a link in the neuronal circuitry underlying these processes. In our study, pulses were given at ZT14 (i.e. phase delaying). Thus, it is plausible that enhanced masking responses of Per1−/− mice is mediated by neural processing of light by the SCN.
Aging-related changes on social synchronization of circadian activity rhythm in a diurnal primate (Callithrix jacchus)
Published in Chronobiology International, 2020
Fabiana B. Gonçalves, Bruno S. B. Gonçalves, Jeferson S. Cavalcante, Carolina V. M. Azevedo
The response of the CAR to social cues in adults raises the possibility that conspecific vocalizations could be acting on the circadian timing system by an indirect way. The synchronization of free-running rhythm with τ < 24 h occurred when vocalizations coincided with the end of the activity phase. This response indicates that adjustment of the rhythm occurred by phase delay, and this is compatible with the photic responses observed on the phase response curve for this species (Glass et al. 2001; Wechselberger and Erkert 1994). Thus, we suggest the arousal elicited by the nonphotic cues increases the photic input on the circadian timing system, as suggested by Wechselberger (1994), who evaluated the effect of playback calls from conspecifics in front of a mirror on the CAR of marmosets.