Dim Nocturnal Illumination and Plasticity of Circadian Entrainment

在人类和其他哺乳动物中，行为和生理功能的显著日常变化是由内源性神经钟产生的，这些神经钟通过从视网膜到大脑的直接和间接神经投射与光环境同步。以前的工作已经表明，明亮的光是重置生物钟的相位所必需的，并且已经在视网膜中发现了对光具有匹配敏感性的细胞。目前的项目探索非常微弱的光(强度低于暗淡的月光)对昼夜节律系统的新行为。与预期相反，初步研究表明，暗淡的夜间光照导致昼夜节律功能发生显著变化：在它的存在下，动物更容易适应昼长的季节性变化；它们更成功地将它们的节律缠绕到非24小时天数，并在双峰24小时光：暗：光：暗周期下将它们的昼夜节律重组为多个分量。在一系列行为研究中，该项目探索了这样一种假设，即暗光通过改变组成昼夜节律振荡器之间的耦合或相互作用来发挥作用。此外，研究人员还检查了暗光的波长和强度要求，以评估调节其影响的视网膜光感受器。最后，在丘脑膝间小叶受损的动物身上检验了这些影响，通过丘脑的中脑视觉投射上升到昼夜节律起搏器。这些研究可能会为快速操纵人类昼夜节律提供新的途径。这些发现可能对优化人类在轮班工作、跨子午线和太空旅行以及其他情况下的表现有价值。

In humans and other mammals, marked daily variations in behavioral and physiological function are generated by endogenous neural clocks, which are synchronized with the light environment through both direct and indirect neural projections from the retina to the brain. Previous work has shown that bright light is necessary to reset the phase of circadian clocks, and cells with matching sensitivity to light have been identified in the retina. The present project explores novel actions of very dim light (less intense than dim moonlight) on the circadian system. Counter to expectations, preliminary studies show that dim nocturnal illumination results in marked changes in circadian function: in its presence, animals more readily adjust to seasonal changes in daylength; they entrain their rhythms more successfully to non 24-h days and they reorganize their circadian rhythms into multiple components under bimodal 24-h light:dark:light:dark cycles. In a series of behavioral studies, this project explores the hypothesis that dim light exerts its effects by altering the coupling, or interactions, between component circadian oscillators. Further, the investigators examine the wavelength and intensity requirements of dim light to assess the retinal photoreceptors that mediate its effects. Finally, these effects are examined in animals with lesions of the intergeniculate leaflet of the thalamus through which midbrain visual projections ascend to the circadian pacemaker. These studies may suggest new avenues for rapid manipulation of human circadian rhythms. These findings may be of value in optimizing human performance during shift-work, in trans-meridian and space travel, and in other contexts.