Circadian Waveform and Its Significance for Clock Organization and Plasticity

Gorman, Michael R.; Harrison, Elizabeth; Evans, Jennifer

doi:10.1007/978-81-322-3688-7_4

Cited by 5 publications

(11 citation statements)

References 59 publications

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“…Recent experiments on mice revealed that bifurcation of activity occurs only in the presence of LDLD cycles only when the dark phase has dim illumination (Harrison et al, 2016). This has been attributed to the effect of constant light on the inter-neuronal coupling of the circadian network (Gorman et al, 2017). However, in our experiments, we used LDLD to induce bifurcation in flies with complete darkness during the dark phase.…”

Section: Methodsmentioning

confidence: 99%

“…Plasticity in response to varying light conditions has been studied extensively in rodents over the past several decades (Gorman et al, 2017; Gorman and Elliott, 2003, 2004; Harrison et al, 2016; Pittendrigh and Daan, 1976). Few such studies have revealed that 2 light/dark (LD) cycles of short periodicity (e.g., 12 h) within one 24-h day (LDLD) are perceived by nocturnal rodents as an opportunity to bifurcate their activity patterns into 2 bouts, 1 in each of the dark phases.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the ability of organisms to show such bifurcation is thought to be dependent on the rigidity or lability of the circadian clock network (Gorman et al, 2017), thereby illustrating the utility of such unique, albeit unnatural environments in understanding the physiological regulation of plasticity. However, such studies have been restricted only to rodents, and we concur with the idea that understanding the functional significance of the clock’s ability to show such patterns of plasticity can be comprehensive only if we examine such behaviors in organisms from diverse taxa (as also discussed in Gorman et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Waveform Plasticity under Entrainment to 12-h T-cycles in Drosophila melanogaster: Behavior, Neuronal Network, and Evolution

et al. 2020

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A crucial property of circadian clocks is the ability to regulate the shape of an oscillation over its cycle length (waveform) appropriately, thus enhancing Darwinian fitness. Many studies over the past decade have revealed interesting ways in which the waveform of rodent behavior could be manipulated, one of which is that the activity bout bifurcates under environments that have 2 light/dark cycles within one 24-h day (LDLD). It has been observed that such unique, although unnatural, environments reveal acute changes in the circadian clock network. However, although adaptation of waveforms to different photoperiods is well studied, modulation of waveforms under LDLD has received relatively less attention in research on insect rhythms. Therefore, we undertook this study to ask the following questions: what is the extent of waveform plasticity that Drosophila melanogaster exhibits, and what are the neuronal underpinnings of such plasticity under LDLD? We found that the activity/rest rhythms of wild-type flies do not bifurcate under LDLD. Instead, they show similar but significantly different behavior from that under a long-day LD cycle. This behavior is accompanied by differences in the organization of the circadian neuronal network, which include changes in waveforms of a core clock component and an output molecule. In addition, to understand the functional significance of such variations in the waveform, we examined laboratory selected populations that exhibit divergent eclosion chronotypes (and therefore, waveforms). We found that populations selected for predominant eclosion in an evening window ( late chronotypes) showed reduced amplitude plasticity and increased phase plasticity of activity/rest rhythms. This, we argue, is reflective of divergent evolution of circadian neuronal network organization in our laboratory selected flies.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Waveform Plasticity under Entrainment to 12-h T-cycles in Drosophila melanogaster: Behavior, Neuronal Network, and Evolution

et al. 2020

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“…Combining the observations from all studies, activity rhythms during or following bifurcation and extreme T-cycles appear to be more directly controlled by light than driven by a strong underlying circadian oscillator. At the same time, an explanation of only positive and negative masking of a strong oscillator driving behavior in these conditions has also been rejected by prior evidence [13,14,16,17,[20][21][22][23][24][25][48][49][50] as well as by the lack of 24 h rhythmicity in Study 3/Continental ( Figure 6). Therefore, we propose an alternative explanation that remains to be empirically tested.…”

Section: Mechanisms Of Behavioral Adaptationmentioning

confidence: 99%

“…By what mechanism are mice able to adapt their behavior to these highly artificial schedules? A variety of studies with different light cycles and species show converging evidence that an explanation of simple masking can be rejected in favor of a true reorganization of the circadian system [13,14,16,17,[20][21][22][23][24][25][48][49][50]. Whereas Study 2/DuPont and 3/Continental took a phenomenological approach to explore overall entrainment under complex photoperiod regimes, Study 1/Jitter was designed to test specific entrainment hypotheses by evaluating oscillator characteristics in bifurcation and T-cycle entrainment in two ways.…”

Section: Mechanisms Of Behavioral Adaptationmentioning

confidence: 99%

Enhanced Circadian Entrainment in Mice and Its Utility under Human Shiftwork Schedules

et al. 2019

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The circadian system is generally considered to be incapable of adjusting to rapid changes in sleep/work demands. In shiftworkers this leads to chronic circadian disruption and sleep loss, which together predict underperformance at work and negative health consequences. Two distinct experimental protocols have been proposed to increase circadian flexibility in rodents using dim light at night: rhythm bifurcation and T-cycle (i.e., day length) entrainment. Successful translation of such protocols to human shiftworkers could facilitate alignment of internal time with external demands. To assess entrainment flexibility following bifurcation and exposure to T-cycles, mice in Study 1 were repeatedly phase-shifted. Mice from experimental conditions rapidly phase-shifted their activity, while control mice showed expected transient misalignment. In Study 2 and 3, mice followed a several weeks-long intervention designed to model a modified DuPont or Continental shiftwork schedule, respectively. For both schedules, bifurcation and nocturnal dim lighting reduced circadian misalignment. Together, these studies demonstrate proof of concept that mammalian circadian systems can be rendered sufficiently flexible to adapt to multiple, rapidly changing shiftwork schedules. Flexible adaptation to exotic light-dark cycles likely relies on entrainment mechanisms that are distinct from traditional entrainment.

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Reorganization of circadian activity and the pacemaker circuit under novel light regimes

Sharma,

Sheeba

2024

Proc. R. Soc. B.

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Many environmental features are cyclic, with predictable changes across the day, seasons and latitudes. Additionally, anthropogenic, artificial-light-induced changes in photoperiod or shiftwork-driven novel light/dark cycles also occur. Endogenous timekeepers or circadian clocks help organisms cope with such changes. The remarkable plasticity of clocks is evident in the waveforms of behavioural and molecular rhythms they govern. Despite detailed mechanistic insights into the functioning of the circadian clock, practical means to manipulate activity waveform are lacking. Previous studies using a nocturnal rodent model showed that novel light regimes caused locomotor activity to bifurcate such that mice showed two bouts of activity restricted to the dimly lit phases. Here, we explore the generalizability of these findings and leverage the genetic toolkit of Drosophila melanogaster to obtain mechanistic insights into this unique phenomenon. We find that dim scotopic illumination of specific durations induces circadian photoreceptor CRYPTOCHROME-dependent activity bifurcation in male flies. We show circadian reorganization of the pacemaker circuit, wherein the ‘evening’ neurons regulate the timing of both bouts of activity under novel light regimes. Our findings indicate that such environmental regimes can be exploited to design light cycles, which can ease the circadian waveform into synchronizing with challenging conditions.

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Circadian Waveform and Its Significance for Clock Organization and Plasticity

Cited by 5 publications

References 59 publications

Waveform Plasticity under Entrainment to 12-h T-cycles in Drosophila melanogaster: Behavior, Neuronal Network, and Evolution

Waveform Plasticity under Entrainment to 12-h T-cycles in Drosophila melanogaster: Behavior, Neuronal Network, and Evolution

Enhanced Circadian Entrainment in Mice and Its Utility under Human Shiftwork Schedules

Reorganization of circadian activity and the pacemaker circuit under novel light regimes

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