Gorman Michael R, Elliott Jeffrey A
Departments of Psychology, University of California, San Diego, La Jolla, CA 92093-0109, USA.
J Biol Rhythms. 2003 Dec;18(6):502-12. doi: 10.1177/0748730403260219.
Recent work with exotic 24-h light:dark:light:dark (LDLD) cycles indicates surprising flexibility in the entrainment patterns of Syrian hamsters. Following exposure to an LDLD cycle, hamsters may adopt a form of rhythm splitting in which markers of subjective night (e.g., activity, melatonin) are expressed in each of the twice daily scotophases. This pattern contrasts markedly with that of conventionally entrained hamsters in which markers of subjective night are expressed once daily in only 1 of the 2 dark periods. The "split" entrainment pattern was examined further here in Syrian and Siberian hamsters and in mice exposed to LDLD 7:5:7:5, a condition that reliably induces split activity rhythms in all 3 species. The phase angle of entrainment and activity duration were generally similar comparing the 2 daily activity bouts in each species. The stability of this split entrainment state was assessed by deletions of photophases on individual days, by exposure to skeleton photoperiods, and by transfer to constant darkness. As in Syrian hamsters, the one-time substitution of darkness for one 7-h photophase did not grossly alter activity patterns of Siberian hamsters but acutely disrupted the split rhythms of mice. Skeleton light pulses of progressively shorter duration did not significantly alter split entrainment patterns of either Syrian or Siberian hamsters. Both species continued to exhibit stable entrainment with activity expressed in alternate scotophases of an LD 1:5 cycle presented 4 times daily. In contrast, the split activity rhythms of mice were not maintained under skeleton pulses. In constant darkness, rhythms of Siberian hamsters remained distinctly split for a minimum of 2 cycles. Split entrainment to these novel LDLD and 4-pulse skeleton lighting regimes demonstrates a marked degree of plasticity common to the circadian systems of several rodent species and identifies novel entrainment patterns that may be reliably elicited with simple environmental manipulations. Inter- and intraspecific differences in the stability of split activity rhythms likely reflect differences in coupling interactions between the component circadian oscillators, which, adopting separate phase relations to these novel LD cycles, yield a split entrainment pattern.
近期关于奇异的24小时明:暗:明:暗（LDLD）周期的研究表明，叙利亚仓鼠的昼夜节律调节模式具有惊人的灵活性。在暴露于LDLD周期后，仓鼠可能会采用一种节律分裂的形式，即主观夜间的标志物（如活动、褪黑素）在每天两次的暗期均有表达。这种模式与传统昼夜节律调节的仓鼠明显不同，在传统调节的仓鼠中，主观夜间的标志物仅在两个暗期之一中每天表达一次。在此，我们进一步研究了叙利亚仓鼠、西伯利亚仓鼠以及暴露于LDLD 7:5:7:5条件下的小鼠的“分裂”昼夜节律调节模式，该条件能可靠地在所有这三个物种中诱导出分裂活动节律。比较每个物种的两次日常活动时段，其昼夜节律调节的相位角和活动持续时间通常相似。通过在个别日子删除光照期、暴露于骨架光周期以及转移到持续黑暗环境中来评估这种分裂昼夜节律调节状态的稳定性。与叙利亚仓鼠一样，将一个7小时的光照期一次性替换为黑暗期并不会显著改变西伯利亚仓鼠的活动模式，但会严重扰乱小鼠的分裂节律。持续时间逐渐缩短的骨架光脉冲并不会显著改变叙利亚或西伯利亚仓鼠的分裂昼夜节律调节模式。这两个物种在每天呈现4次的LD 1:5周期的交替暗期内继续表现出稳定的昼夜节律调节且有活动。相比之下，小鼠的分裂活动节律在骨架脉冲下无法维持。在持续黑暗环境中，西伯利亚仓鼠的节律至少在两个周期内仍保持明显的分裂状态。对这些新颖的LDLD和4脉冲骨架光照模式的分裂昼夜节律调节表明，几种啮齿动物物种的昼夜节律系统具有显著程度的可塑性，并确定了可以通过简单环境操纵可靠诱发的新颖昼夜节律调节模式。分裂活动节律稳定性的种间和种内差异可能反映了组成昼夜节律振荡器之间耦合相互作用的差异，这些振荡器与这些新颖的LD周期采用不同的相位关系，从而产生分裂昼夜节律调节模式。
