Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Spain.
Chronobiol Int. 2012 Jul;29(6):693-701. doi: 10.3109/07420528.2012.680556.
Circadian rhythms are strongly influenced by light intensity, the effects of which may persist beyond the duration of light exposure (aftereffects). Here, the authors constructed period-illuminance curves for the motor activity circadian rhythm of male and female rats by recording the effects of a series of small upward and downward steps in light intensity (illuminance ranging between .01 lux of dim red light and 1 lux of white light) on their activity. In all cases, stepwise changes were made in five logarithmic steps (irradiance: dim red light: .692 µW/cm(2) and white light: .006, .016, .044, .12, and .315 µW/cm(2), corresponding, respectively, to .02, .05, .14, .13, and 1 lux measured at cage level), with changes in intensity every 2 wks. One group of rats (DLD) started in dim red light, moved up to 1 lux white light, and then back down to the original light intensity. Another group (LDL) started at 1 lux, moved down to .01 lux, and then back up to the original intensity. Motor activity data were recorded throughout the experiment and tau values, the percentage of variance explained by the rhythm, and the mean motor activity for each stage and group were calculated. The results show differences in the dynamics of tau values between the DLD and LDL groups and between males and females. In the LDL group, the tau values of both males and females were dependent on light intensity, and were similar for the forward and backward transitions. In other words, no aftereffects were found, and no differences were detected between males and females. In the DLD group, however, differences were found between males and females. Males had a tau value of 24 h 20 min under dim red light, 25 h 40 min under 1 lux, and 24 h 50 min on return to dim red light. It is noticeable that the tau values of the backward branch of the illuminance curve contradicted classical predictions, since at .38 and .14 lux the tau values were shorter than those found under the same intensities after exposure to 1 lux. Females became arrhythmic at 1 lux, and only one half of them recovered their circadian rhythm at .02 lux. The other one half remained arrhythmic even under dim red light. Thus, some of the results of this paper contradict the predictions of standard descriptions of the functioning of the circadian clock, possibly due to the effects of dim light.
昼夜节律强烈地受到光强度的影响，其效应可能会持续超过光暴露的持续时间（后效）。在这里，作者通过记录一系列光强度（照度范围在.01 勒克斯的暗红色光和 1 勒克斯的白光之间）的小上升和下降步骤对雄性和雌性大鼠的运动活动昼夜节律的影响，构建了它们的周期-照度曲线。在所有情况下，以五个对数步（辐照度：暗红色光：.692 µW/cm(2)和白光：.006、.016、.044、.12 和.315 µW/cm(2)，分别对应于在笼子水平测量的.02、.05、.14、.13 和 1 勒克斯）进行逐步变化，强度每 2 周变化一次。一组大鼠（DLD）从暗红色光开始，移动到 1 勒克斯的白光，然后再回到原来的光强度。另一组（LDL）从 1 勒克斯开始，移动到.01 勒克斯，然后再回到原来的强度。在整个实验过程中记录运动活动数据，并计算每个阶段和组的 tau 值、节律解释的方差百分比以及平均运动活动。结果表明，DLD 和 LDL 组之间以及雄性和雌性之间的 tau 值动态存在差异。在 LDL 组中，雄性和雌性的 tau 值都依赖于光强度，并且向前和向后的转变相似。换句话说，没有后效，也没有发现雄性和雌性之间的差异。然而，在 DLD 组中，发现了雄性和雌性之间的差异。雄性在暗红色光下的 tau 值为 24 小时 20 分钟，在 1 勒克斯下为 25 小时 40 分钟，在返回暗红色光下为 24 小时 50 分钟。值得注意的是，照度曲线的向后分支的 tau 值与经典预测相矛盾，因为在.38 和.14 勒克斯时，tau 值比在暴露于 1 勒克斯时在相同强度下发现的要短。雌性在 1 勒克斯时变得无节律，只有一半的雌性在.02 勒克斯时恢复了昼夜节律。另一半即使在暗红色光下也保持无节律。因此，本文的一些结果与昼夜节律钟功能的标准描述的预测相矛盾，可能是由于暗光的影响。
