Weinert D, Weinert H
Institute of Zoology, Martin-Luther-University Halle-Wittenberg, Germany.
Chronobiol Int. 2003 May;20(3):405-16. doi: 10.1081/cbi-120021038.
The daily activity pattern of old mice is characterized by a decreased amplitude, a phase advance, and less stable relationship between lights-off and the onset of the main activity maximum. When analyzing the possible causes of these changes, it must be remembered that the activity rhythm of laboratory mice is bimodal, with a main peak in the first half of the dark time and a secondary one shortly after lights-on. Thus it seems to be controlled by at least two circadian oscillators--an "evening oscillator" coupled more strongly to lights-off and a "morning oscillator" coupled to lights-on--though both oscillators are also coupled to each other. The objective of the present paper was to investigate the putative changes in the strength of these couplings in HaZ:ICR mice of different ages (adult animals of 20 weeks, n = 12; old mice of 72 and 91 weeks of age, n = 6 each) and kept in a 24 h LD-cycle with a gradually reduced light:dark ratio. In adult mice, lengthening the dark time caused the onset of the main maximum of activity to be delayed in relation to the time of lights-off, while the morning maximum of activity was advanced in relation to lights-on. On average, the sizes of the advance and the delay were equal. As a consequence, the activity pattern did not shift in relation to the middle of the dark time. Lengthening the dark time resulted in a bigger (on average, 1.5 h) difference between the evening and morning activity onsets. Under short photoperiods (< or = 2 h of light) the activity rhythm started to free run, and the difference between evening and morning activity onsets decreased again. The changes obtained in senile mice were similar. However, the limits of entrainment were reached with longer photoperiods compared to adult animals. Also, the phase delay of the activity onset in the evening was much less, nearly zero. As a consequence, the activity pattern as whole phase-advanced in relation to the middle of the dark time. A model was proposed in which lights-off triggers advances of the "evening oscillator," lights-on delays the "morning oscillator," and the two oscillators are coupled with each other. Though it was probably the case, decreased coupling strengths could not be shown with the present experimental approach. However, it was clearly evident that, with increasing age, the advancing effect of lights-off exceeded the delaying effect of lights-on.
老年小鼠的日常活动模式具有振幅减小、相位提前以及熄灯与主要活动高峰开始之间的关系不太稳定的特点。在分析这些变化的可能原因时，必须记住实验室小鼠的活动节律是双峰的，在黑暗时间的前半段有一个主峰，在开灯后不久有一个次峰。因此，它似乎至少由两个昼夜节律振荡器控制——一个“傍晚振荡器”与熄灯的耦合更强，一个“早晨振荡器”与开灯的耦合更强——尽管这两个振荡器也相互耦合。本文的目的是研究不同年龄（20周龄的成年动物，n = 12；72周龄和91周龄的老年小鼠，各n = 6）的哈茨：ICR小鼠在逐渐降低光暗比的24小时明暗循环中，这些耦合强度的假定变化。在成年小鼠中，延长黑暗时间会导致主要活动高峰的开始相对于熄灯时间延迟，而早晨的活动高峰相对于开灯时间提前。平均而言，提前和延迟的幅度相等。因此，活动模式相对于黑暗时间的中间没有发生偏移。延长黑暗时间导致傍晚和早晨活动开始之间的差异更大（平均为1.5小时）。在短光周期（≤2小时光照）下，活动节律开始自由运行，傍晚和早晨活动开始之间的差异再次减小。老年小鼠获得的变化类似。然而，与成年动物相比，在更长的光周期下达到了同步的极限。此外，傍晚活动开始的相位延迟要小得多，几乎为零。因此，整个活动模式相对于黑暗时间的中间提前了。提出了一个模型，其中熄灯触发“傍晚振荡器”的提前，开灯延迟“早晨振荡器”，并且这两个振荡器相互耦合。虽然可能是这种情况，但用目前的实验方法无法显示耦合强度的降低。然而，很明显，随着年龄的增长，熄灯的提前效应超过了开灯的延迟效应。
