Department of Psychology, University of California, San Diego, La Jolla, CA, USA.
J Biol Rhythms. 2012 Oct;27(5):410-9. doi: 10.1177/0748730412455915.
Because the circadian clock in the mammalian brain derives from a network of interacting cellular oscillators, characterizing the nature and bases of circadian coupling is fundamental to understanding how the pacemaker operates. Various phenomena involving plasticity in circadian waveform have been theorized to reflect changes in oscillator coupling; however, it remains unclear whether these different behavioral paradigms reference a unitary underlying process. To test whether disparate coupling assays index a common mechanism, we examined whether there is covariation among behavioral responses to various lighting conditions that produce changes in circadian waveform. Siberian hamsters, Phodopus sungorus, were transferred from long to short photoperiods to distinguish short photoperiod responders (SP-R) from nonresponders (SP-NR). Short photoperiod chronotyped hamsters were subsequently transferred, along with unselected controls, to 24-h light:dark:light: dark cycles (LDLD) with dim nighttime illumination, a procedure that induces bifurcated entrainment. Under LDLD, SP-R hamsters were more likely to bifurcate their rhythms than were SP-NR hamsters or unselected controls. After transfer from LDLD to constant dim light, SP-R hamsters were also more likely to become arrhythmic compared to SP-NR hamsters and unselected controls. In contrast, short photoperiod chronotype did not influence more transient changes in circadian waveform. The present data reveal a clear relationship in the plasticity of circadian waveform across 3 distinct lighting conditions, suggesting a common mechanism wherein individual differences reflect variation in circadian coupling.
由于哺乳动物大脑中的生物钟源自相互作用的细胞振荡器网络，因此描述生物钟耦合的本质和基础对于理解生物钟如何运作至关重要。各种涉及生物钟波形可塑性的现象被认为反映了振荡器耦合的变化；然而，目前尚不清楚这些不同的行为范式是否参考了一个统一的潜在过程。为了测试不同的耦合测定是否指数一个共同的机制，我们研究了在产生生物钟波形变化的各种光照条件下，行为反应之间是否存在协变。将西伯利亚仓鼠（Phodopus sungorus）从长光照周期转移到短光照周期，以区分短光照周期反应者（SP-R）和非反应者（SP-NR）。随后，将短光照周期定型的仓鼠与未经选择的对照一起转移到 24 小时光照：黑暗：光照：黑暗循环（LDLD），并伴有夜间弱照明，这一过程会诱导分叉节律同步。在 LDLD 下，SP-R 仓鼠比 SP-NR 仓鼠或未经选择的对照更有可能分叉他们的节律。从 LDLD 转移到恒定的弱光照后，与 SP-NR 仓鼠和未经选择的对照相比，SP-R 仓鼠也更有可能变得无节奏。相比之下，短光照周期定型并不影响生物钟波形更短暂的变化。本研究的数据揭示了 3 种不同光照条件下生物钟波形可塑性之间的明显关系，表明存在一种共同的机制，其中个体差异反映了生物钟耦合的变化。
