Boulos Z, Morin L P
Long Island Research Institute, State University of New York, Stony Brook 11794.
J Biol Rhythms. 1985;1(1):1-15. doi: 10.1177/074873048600100103.
Hamsters that showed splitting of their circadian rhythms of wheel-running activity following long-term exposure to constant illumination (LL) were exposed to light-dark (LD) cycles with 2-hr dark segments, and with periods of 24.00, 24.23 or 24.72 hr. For comparison, hamsters showing nonsplit rhythms were also studied. In all cases of split rhythms, at least one of the two split components entrained to the LD cycles. In some animals, the second component continued to free-run until it merged with the entrained component, while in others, the second component also entrained to the LD cycle but maintained a stable phase angle of 6-14.5 hr relative to dark onset. These results were obtained in cases where the period of the LD cycle was shorter than that of the split rhythms and in cases where it was longer, implying that split components can be phase-advanced as well as phase-delayed by 2 hr of darkness. Three hamsters that showed stable entrainment of split rhythms were allowed to free-run in LL. The LD cycles were then reinstated, but instead of overlapping with the first component, as it did before, the dark segment was timed to overlap with the second. The entrainment patterns that ensued were similar to the ones obtained during the first LD exposure, indicating that the two split components respond to darkness in a qualitatively similar fashion. These results are further evidence that the pacemaker system underlying split circadian activity rhythms in hamsters is composed of two mutually coupled populations of oscillators that have similar properties, including a bidirectional phase response curve. Such a dual-oscillator organization may also underlie normal, or nonsplit, activity rhythms, as suggested by Pittendrigh and Daan (1976c), but the data are also compatible with the alternative view that the circadian pacemaker consists of a large number of coupled oscillators, which only dissociate into two separate populations in some animals under conditions of moderate LL intensity.
长期暴露于持续光照（LL）后出现昼夜节律性轮转活动分裂的仓鼠，被置于明暗（LD）周期中，暗期为2小时，周期分别为24.00、24.23或24.72小时。为作比较，也对表现出非分裂节律的仓鼠进行了研究。在所有分裂节律的情况下，两个分裂成分中至少有一个与LD周期同步。在一些动物中，第二个成分继续自由运行，直到与同步成分合并，而在另一些动物中，第二个成分也与LD周期同步，但相对于暗期开始保持6 - 14.5小时的稳定相位角。这些结果在LD周期的时长比分裂节律短以及比分裂节律长的情况下均能获得，这意味着分裂成分可通过2小时的黑暗实现相位提前以及相位延迟。三只表现出分裂节律稳定同步的仓鼠被置于LL中自由运行。随后恢复LD周期，但与之前不同，不是让暗期与第一个成分重叠，而是让暗期与第二个成分重叠。随后出现的同步模式与首次LD暴露时获得的模式相似，表明两个分裂成分对黑暗的反应在性质上相似。这些结果进一步证明，仓鼠昼夜活动节律分裂背后的起搏器系统由两个相互耦合的振荡器群体组成，它们具有相似的特性，包括双向相位响应曲线。正如Pittendrigh和Daan（1976c）所指出的，这种双振荡器组织也可能是正常或非分裂活动节律的基础，但这些数据也与另一种观点相符，即昼夜起搏器由大量耦合振荡器组成，只是在中等LL强度条件下，某些动物中的这些振荡器才会分离成两个独立的群体。
