Guerin M V, Matthews C D
Department of Obstetrics and Gynaecology, University of Adelaide, Queen Elizabeth Hospital, Woodville, South Australia.
J Biol Rhythms. 1998 Feb;13(1):60-9. doi: 10.1177/074873098128999925.
The timing of reproductive activity in the seasonal breeding Romney Marsh ewe depends on the measurement of photoperiodic time. In this experiment, artificial light and dark signals are provided in a measured sequence at an inappropriate time of year to induce breeding out of phase with environmental photoperiod. The endogenous circadian responses and reproductive effects are documented. One group (Group A, control) of 6 Romney Marsh ewes was held in natural photoperiod throughout the experiment. For 8 weeks centered about the winter solstice (Stage 1), an additional 18 animals (Groups B, C, and D) were exposed to an artificial earlier dawn. Measurements of endogenous melatonin performed under acutely extended darkness confirmed a phase advance of the endogenous circadian pacemaker of the suprachiasmatic nucleus compared to control animals. In Stage 2, to the summer solstice (21 December), Group B animals were returned to natural photoperiod, Group C animals were subjected to an earlier artificial dusk, and Group D animals were subjected to an artificial delayed dawn. Melatonin measurements during Stage 2 confirmed that onset and offset times for Group C were earlier and that onset and offset times for Group D were delayed compared to corresponding times for Group B animals. Ovarian activity was monitored throughout. During Stage 2, Groups C and D commenced reproductive activity in mid-spring, and this continued until the experimental conditions changed. Groups A and B commenced reproductive activity at the normal timing in the subsequent autumn. Although not exclusive, these results are consistent with a coincidence model to explain the timing of seasonal breeding in this species with a dusk-located phase of the endogenous pacemaker sensitive to both light and melatonin. The temporal relationship between circadian alterations and the environmental photoperiod warrants further investigation as an explanation for seasonal breeding.
季节性繁殖的罗姆尼沼泽母羊的繁殖活动时间取决于光周期时间的测量。在本实验中，在一年中不合适的时间以测量好的顺序提供人工光暗信号，以诱导繁殖与环境光周期不同步。记录内源性昼夜节律反应和繁殖效应。一组6只罗姆尼沼泽母羊（A组，对照组）在整个实验过程中处于自然光照周期。在以冬至为中心的8周内（第1阶段），另外18只动物（B组、C组和D组）暴露于人工提前的黎明。在急性延长黑暗条件下进行的内源性褪黑素测量证实，与对照动物相比，视交叉上核的内源性昼夜节律起搏器有相位提前。在第2阶段，到夏至（12月21日），B组动物恢复到自然光照周期，C组动物接受提前的人工黄昏，D组动物接受人工延迟的黎明。第2阶段的褪黑素测量证实，与B组动物的相应时间相比，C组的开始和结束时间更早，D组的开始和结束时间延迟。全程监测卵巢活动。在第2阶段，C组和D组在仲春开始繁殖活动，并持续到实验条件改变。A组和B组在随后的秋季正常时间开始繁殖活动。虽然并非唯一，但这些结果与一个巧合模型一致，该模型解释了该物种季节性繁殖的时间，其具有对内源性起搏器的黄昏定位阶段敏感的光和褪黑素。昼夜节律改变与环境光周期之间的时间关系作为季节性繁殖的一种解释值得进一步研究。
