Department of Psychology , University of California, San Diego, La Jolla, California, USA.
Chronobiol Int. 2011 Jul;28(6):488-96. doi: 10.3109/07420528.2011.591952.
The endogenous circadian pacemaker of mammals is synchronized to the environmental day by the ambient cycle of relative light and dark. The present studies assessed the actions of light in a novel circadian entrainment paradigm where activity rhythms are bifurcated following exposure to a 24-h light:dark:light:dark (LDLD) cycle. Bifurcated entrainment under LDLD reflects the temporal dissociation of component oscillators that comprise the circadian system and is facilitated when daily scotophases are dimly lit rather than completely dark. Although bifurcation can be stably maintained in LDLD, it is quickly reversed under constant conditions. Here the authors examine whether dim scotophase illumination acts to maintain bifurcated entrainment under LDLD through potential interactions with the parametric actions of bright light during the two daily photophases. In three experiments, wheel-running rhythms of Syrian hamsters were bifurcated under LDLD with dimly lit scotophases, and after several weeks, dim scotophase illumination was either retained or extinguished. Additionally, "full" and "skeleton" photophases were employed under LDLD cycles with dimly lit or completely dark scotophases to distinguish parametric from nonparametric effects of bright light. Rhythm bifurcation was more stable in full versus skeleton LDLD cycles. Dim light facilitated the maintenance of bifurcated entrainment under full LDLD cycles but did not prevent the loss of rhythm bifurcation in skeleton LDLD cycles. These studies indicate that parametric actions of bright light maintain the bifurcated entrainment state; that dim scotophase illumination increases the stability of the bifurcated state; and that dim light interacts with the parametric effects of bright light to increase the stability of rhythm bifurcation under full LDLD cycles. A further understanding of the novel actions of dim light may lead to new strategies for understanding, preventing, and treating chronobiological disturbances.
哺乳动物的内源性生物钟节律通过环境光暗周期与环境同步。本研究在一个新的生物钟节律重新同步范式中评估了光的作用，即在暴露于 24 小时光暗：光暗：光暗（LDLD）循环后，活动节律出现二分。LDLD 下的二分同步反映了构成生物钟系统的分位振荡器的时间分离，并且当每日的暗相被弱光照亮而不是完全黑暗时，这种分离更容易发生。虽然二分同步可以在 LDLD 下稳定维持，但在恒光条件下会迅速逆转。作者在这里研究了在 LDLD 下，弱暗相光照是否通过与两个每日光相期间强光的参数作用潜在相互作用来维持二分同步。在三个实验中，叙利亚仓鼠的轮跑节律在 LDLD 下出现二分，其中暗相被弱光照亮，几周后，要么保留弱暗相照明，要么熄灭。此外，在 LDLD 循环中使用“全”和“骨架”光相，其中暗相被弱光或完全黑暗照亮，以区分强光的参数和非参数作用。在全光 LDLD 循环中，节律二分比在骨架 LDLD 循环中更稳定。弱光促进了全 LDLD 循环下二分同步的维持，但不能防止骨架 LDLD 循环中节律二分的丧失。这些研究表明，强光的参数作用维持了二分同步状态；弱暗相照明增加了二分状态的稳定性；弱光与强光的参数作用相互作用，增加了全 LDLD 循环下节律二分的稳定性。对弱光新作用的进一步了解可能会为理解、预防和治疗生物钟节律紊乱提供新策略。
