Beersma Domien G M, van Bunnik Bram A D, Hut Roelof A, Daan Serge
Department of Chronobiology, University of Groningen, The Netherlands.
J Biol Rhythms. 2008 Aug;23(4):362-73. doi: 10.1177/0748730408317992.
Daily patterns of behavior and physiology in animals in temperate zones often differ substantially between summer and winter. In mammals, this may be a direct consequence of seasonal changes of activity of the suprachiasmatic nucleus (SCN). The purpose of this study was to understand such variation on the basis of the interaction between pacemaker neurons. Computer simulation demonstrates that mutual electrical activation between pacemaker cells in the SCN, in combination with cellular electrical activation by light, is sufficient to explain a variety of circadian phenomena including seasonal changes. These phenomena are: self-excitation, that is, spontaneous development of circadian rhythmicity in the absence of a light-dark cycle; persistent rhythmicity in constant darkness, and loss of circadian rhythmicity in pacemaker output in constant light; entrainment to light-dark cycles; aftereffects of zeitgeber cycles with different periods; adjustment of the circadian patterns to day length; generation of realistic phase response curves to light pulses; and relative independence from day-to-day variation in light intensity. In the model, subsets of cells turn out to be active at specific times of day. This is of functional importance for the exploitation of the SCN to tune specific behavior to specific times of day. Thus, a network of on-off oscillators provides a simple and plausible construct that behaves as a clock with readout for time of day and simultaneously as a clock for all seasons.
温带地区动物的日常行为和生理模式在夏季和冬季往往有很大差异。对于哺乳动物来说，这可能是视交叉上核（SCN）活动季节性变化的直接结果。本研究的目的是基于起搏器神经元之间的相互作用来理解这种变化。计算机模拟表明，SCN中起搏器细胞之间的相互电激活，与光引起的细胞电激活相结合，足以解释包括季节性变化在内的各种昼夜节律现象。这些现象包括：自我兴奋，即在没有明暗周期的情况下昼夜节律的自发形成；在持续黑暗中的持续节律性，以及在持续光照下起搏器输出中昼夜节律性的丧失；对明暗周期的同步化；不同周期的授时因子周期的后效应；昼夜节律模式对白昼长度的调整；对光脉冲产生现实的相位响应曲线；以及相对独立于光强度的每日变化。在该模型中，细胞亚群在一天中的特定时间被证明是活跃的。这对于利用SCN将特定行为调整到一天中的特定时间具有重要的功能意义。因此，一个开-关振荡器网络提供了一个简单且合理的结构，它既作为一个能读出一天中时间的时钟，又同时作为一个适用于所有季节的时钟。
