Laboratory for Neurophysiology, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, the Netherlands.
J Biol Rhythms. 2014 Feb;29(1):4-15. doi: 10.1177/0748730413516750.
The suprachiasmatic nucleus (SCN) adapts to both the external light-dark (LD) cycle and seasonal changes in day length. In short photoperiods, single-cell activity patterns are tightly synchronized (i.e., in phase); in long photoperiods, these patterns are relatively dispersed, causing lower amplitude rhythms. The limit cycle oscillator has been used to describe the SCN's circadian rhythmicity and predicts that following a given perturbation, high-amplitude SCN rhythms will shift less than low-amplitude rhythms. Some studies reported, however, that phase delays are larger when animals are entrained to a short photoperiod. Because phase advances and delays are mediated by partially distinct (i.e., nonoverlapping) biochemical pathways, we investigated the effect of a 4-h phase advance of the LD cycle in mice housed in either short (LD 8:16) or long (LD 16:8) photoperiods. In vitro recordings revealed a significantly larger phase advance in the SCN of mice entrained to short as compared to long photoperiods (4.2 ± 0.3 h v. 1.4 ± 0.9 h, respectively). Surprisingly, in mice with long photoperiods, the behavioral phase shift was larger than the phase shift of the SCN (3.7 ± 0.4 h v. 1.4 ± 0.9 h, respectively). To exclude a confounding influence of running-wheel activity on the magnitude of the shifts of the SCN, we repeated the experiments in the absence of running wheels and found similar shifts in the SCN in vitro in short and long days (3.0 ± 0.5 h v. 0.4 ± 0.9 h, respectively). Interestingly, removal of the running wheel reduced the phase-shifting capacity of mice in long days, leading to similar behavioral shifts in short and long photoperiods (1.0 ± 0.1 h v. 1.0 ± 0.4 h). As the behavioral shifts in the presence of wheels were larger than the shift of the SCN, it is suggested that additional, non-SCN neuronal networks in the brain are involved in regulating the timing of behavioral activity. On the basis of the phase shifts observed in vitro, we conclude that highly synchronized SCN networks with high-amplitude rhythms show a larger phase-shifting capacity than desynchronized networks of low amplitude.
视交叉上核(SCN)适应外部光-暗(LD)周期和季节性的日长变化。在短光照周期中,单细胞活动模式紧密同步(即同相);在长光照周期中,这些模式相对分散,导致节律幅度较低。限幅振荡器已被用于描述 SCN 的昼夜节律性,并预测在受到给定的干扰后,高振幅 SCN 节律的变化将小于低振幅节律。然而,一些研究报告称,当动物被适应于短光照周期时,相位延迟更大。由于相位提前和延迟是由部分不同的(即不重叠的)生化途径介导的,我们研究了在处于短光照(LD 8:16)或长光照(LD 16:8)周期的小鼠中,LD 周期的 4 小时相位提前对 SCN 的影响。体外记录显示,与长光照周期相比,适应于短光照周期的小鼠 SCN 的相位提前明显更大(分别为 4.2 ± 0.3 h 和 1.4 ± 0.9 h)。令人惊讶的是,在长光照周期的小鼠中,行为相位的变化大于 SCN 的相位变化(分别为 3.7 ± 0.4 h 和 1.4 ± 0.9 h)。为了排除跑轮活动对 SCN 变化幅度的混杂影响,我们在没有跑轮的情况下重复了实验,发现短光照和长光照下 SCN 的体外变化相似(分别为 3.0 ± 0.5 h 和 0.4 ± 0.9 h)。有趣的是,去除跑轮减少了长光照下小鼠的相位转移能力,导致短光照和长光照下的行为变化相似(1.0 ± 0.1 h 和 1.0 ± 0.4 h)。由于有轮时的行为变化大于 SCN 的变化,因此表明大脑中额外的非 SCN 神经元网络参与调节行为活动的时间。基于体外观察到的相位变化,我们得出结论,具有高振幅节律的高度同步 SCN 网络比振幅低的去同步网络具有更大的相位转移能力。