Phase and Period Responses of the Circadian System of Mice (Mus musculus) to Light Stimuli of Different Duration

Abstract

Phase and period responses of the circadian system of mice (Mus musculus) to light stimuli of different duration Comas, M.; Beersma, D. G. M.; Spoelstra, K.; Daan, S. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. In nature, virtually all circadian rhythms assume the 24.0-h period of the solar day-night cycle. This is due to the entrainment of the endogenous oscillators to the external light-dark cycle, the dominant zeitgeber for the majority of organisms. The process of entrainment is based on differential phase and period responses of the circadian systems to light depending on the phase at which the stimulus is applied. The (1, 3, 4, 6, 9, 12, and 18 h) given once per 11 days in otherwise constant darkness. Light-pulse duration affected both amplitude and shape of the phase response curve. Nine-hour light pulses yielded the maximal amplitude PRC. As in other systems, the circadian period slightly lengthened following delays and shortened following advances. The authors aimed to understand how different parts of the light signal contribute to the eventual phase shift. When PRCs were plotted using the onset, midpoint, and end of the pulse as a phase reference, they corresponded best with each other when using the mid-pulse. Using a simple phase-only model, the authors explored the possibility that light affects oscillator velocity strongly in the 1st hour and at reduced strength in later hours of the pulse due to photoreceptor adaptation. They fitted models based on the 1-h PRC to the data for all light pulses. The best overall correspondence between PRCs was obtained when the effect of light during all hours after the first was reduced by a factor of 0.22 relative to the 1st hour. For the predicted PRCs, the light action centered on average at 38% of the light pulse. This is close to the reference phase yielding best correspondence at 36% of the pulses. The result is thus compatible with an initial major contribution of the onset of the light pulse followed by a reduced effect of light responsible for the differences between PRCs for different duration pulses. The authors suggest that the mid-pulse is a better phase reference than lights-on to plot and compare PRCs of different light-pulse durations.

Sensitivity Measures for Oscillating Systems: Application to Mammalian Circadian Gene Network

“…Figure 5C and D illustrates the APRC to light (APRC L ) for pulse durations of 3 and 1 circadian hours, respectively. The shape corresponds very closely to that of experimental data, showing the so-called "deadzone" during the subjective day, with delays early in the subjective evening and advances in late subjective evening [36].…”

“…For example, the light-signaling pathway is now understood to be composed of gates [36] which modulate the signal shape. As the models become more mechanistic, we must study the response to signals displaying properties such as attenuation and continuous (rather than discrete) transitions.…”

Can light make us bright? Effects of light on cognition and sleep

“…pulse duration affects both amplitude and shape of the PRC (Comas et al, 2006). Using a model in which only phase shifts but no period or amplitude changes to light pulses were included, the authors concluded that phase-shifting effects are largest in the first hour of the light pulse, and reduce to a factor 0.22 during all hours after the first hour.…”

Reciprocity between phase shifts and amplitude changes in the mammalian circadian clock

“…In mammals, photostimuli generally produce type 1 PRCs characterized by smaller phase shifts (35,36) of the overt behavioral rhythms. Type 0 PRCs produced by brief, light stimuli are commonly described in bacteria, fungi, and plants, which harbor cell autonomous photopigments.…”