Walbeek Thijs J, Joye Deborah A M, Mishra Ila, Gorman Michael R
Department of Psychology, University of California San Diego, La Jolla, CA 92093, United States of America; Center for Circadian Biology, University of California San Diego, La Jolla, CA 92093, United States of America.
Department of Psychology, University of California San Diego, La Jolla, CA 92093, United States of America; Center for Circadian Biology, University of California San Diego, La Jolla, CA 92093, United States of America.
Physiol Behav. 2019 Oct 15;210:112625. doi: 10.1016/j.physbeh.2019.112625. Epub 2019 Jul 17.
Under permissive conditions, mice and hamsters exposed to a polyphasic light regime consisting of two light and two dark phases every 24 h (Light:Dark:Light:Dark; LDLD) can adopt a bifurcated entrainment pattern with roughly equal amounts of running wheel activity in each of the two nights. This rhythm "bifurcation" has significant after-effects on increased circadian adaptability: Mice that have been bifurcated show accelerated rates of re-entrainment after a sudden phase shift and have a markedly expanded range of entrainment. Identifying environmental and physiological factors that facilitate or prevent rhythm bifurcation in LDLD conditions will contribute to an understanding of mechanisms underlying enhanced circadian plasticity. Here we investigate the effects of sex, age, light intensity, access to a running wheel, melatonin, and diet composition on bifurcation behaviors of mice (C57Bl/6 J) exposed to LDLD. Female mice and young mice (<20 weeks) express more symmetrically bifurcated activity compared to male mice and older mice (>30 weeks). Additionally and independently, higher photophase intensities (500 lx) predict more symmetric entrainment than low levels of light (50 lx). Without access to a functional running-wheel, mice do not adopt bimodal activity patterns and only transiently maintain them, suggesting that high levels of aerobic activity are necessary for rhythm bifurcation. Neither a lifetime exposure to melatonin administered in the drinking water nor a high fat diet affected bifurcation. Collectively, these results demonstrate that circadian plasticity can be strongly modulated by intrinsic and extrinsic factors. With enhanced mechanistic understanding of this modulation, it may be possible to render human clocks more adaptable and thereby ameliorate negative consequences associated with repeated jet-lag or shift-work.
在宽松条件下，暴露于每24小时包含两个光照期和两个黑暗期（光照：黑暗：光照：黑暗；LDLD）的多相光照模式下的小鼠和仓鼠，能够采用一种分叉式的昼夜节律模式，在两个夜晚中各自具有大致等量的转轮活动。这种节律“分叉”对昼夜节律适应性的增强具有显著的后续影响：经历过分叉的小鼠在突然的相位偏移后表现出重新同步化的加速速率，并且具有明显扩大的同步化范围。确定在LDLD条件下促进或阻止节律分叉的环境和生理因素，将有助于理解昼夜节律可塑性增强的潜在机制。在此，我们研究了性别、年龄、光照强度、是否有转轮、褪黑素和饮食组成对暴露于LDLD的小鼠（C57Bl/6 J）分叉行为的影响。与雄性小鼠和老年小鼠（>30周）相比，雌性小鼠和幼年小鼠（<20周）表现出更对称的分叉活动。此外且独立地，较高的光照期强度（约500勒克斯）比较低的光照水平（约50勒克斯）预示着更对称的同步化。如果没有功能性的转轮，小鼠不会采用双峰活动模式，并且只是短暂维持它们，这表明高水平的有氧运动对于节律分叉是必要的。无论是终生饮用添加褪黑素的水，还是高脂饮食，都不会影响分叉。总的来说，这些结果表明，昼夜节律可塑性可受到内在和外在因素的强烈调节。随着对这种调节机制的深入理解，有可能使人类生物钟更具适应性，从而改善与反复时差反应或轮班工作相关的负面后果。
