Vivanco Pablo, Rol Maria Angeles, Madrid Juan Antonio
Chronobiology Laboratory, Department of Physiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Chronobiol Int. 2009 Feb;26(2):219-41. doi: 10.1080/07420520902768203.
Processes involved in the operation of the circadian pacemaker are well characterized; however; little is known about what mechanisms drive the overt diurnal, nocturnal, or crepuscular behavior in a species. In this context, dual-phasing rodents, such as Octodon degus, emerge as a useful model to decipher these keys. Two main chronotypes, nocturnal and diurnal, have been traditionally described in laboratory-housed degus based on the percentage of activity displayed by the animals during the scotophase or photophase. However, if one considers also the entrainment phase angle during the first days following a change from LD to DD conditions, a third chronotype (intermediate)-or more properly, a continuous grading of circadian expressions between diurnal and nocturnal chronotype-can be observed. Our experiments suggest the pacemaker of the diurnal animal is entrained to the photophase, and light does not exert a negative masking effect. The pacemaker of the nocturnal degus, on the other hand, is entrained to the scotophase, and light exerts a strong negative masking effect. Finally, the intermediate chronotype is characterized by variable negative masking effect of light overlapping a pacemaker entrained to the photophase. The phase shift inversion from diurnal to nocturnal chronotype is related to the availability of a wheel in the cage, and the effect may be located downstream from the clock. However, body temperature rhythm recordings, less affected by masking effects, point to an involvement of the circadian pacemaker in chronotype differentiation, as transient entrainment cycles, and not an abrupt phase shift, were detected after providing access to the wheel. The diurnality of degus seems to be the result of a variety of mechanisms, which may explain how different processes can lead to similar chronotypes.
昼夜节律起搏器运作所涉及的过程已得到充分表征；然而，对于驱动一个物种明显的昼行、夜行或晨昏活动行为的机制却知之甚少。在这种背景下，双相性啮齿动物，如八齿鼠，成为解读这些关键问题的有用模型。传统上，基于实验室饲养的八齿鼠在暗期或光期所表现出的活动百分比，已描述了两种主要的昼夜节律类型，即夜行性和昼行性。然而，如果还考虑从光照-黑暗（LD）条件转变为持续黑暗（DD）条件后的头几天内的同步化相位角，就可以观察到第三种昼夜节律类型（中间型）——或者更确切地说，是在昼行性和夜行性昼夜节律类型之间的昼夜节律表达的连续分级。我们的实验表明，昼行性动物的起搏器被同步到光期，并且光不会产生负性掩盖效应。另一方面，夜行性八齿鼠的起搏器被同步到暗期，并且光会产生强烈的负性掩盖效应。最后，中间型昼夜节律类型的特征是光的可变负性掩盖效应与被同步到光期的起搏器重叠。从昼行性到夜行性昼夜节律类型的相移反转与笼中是否有转轮有关，并且这种效应可能位于生物钟的下游。然而，受掩盖效应影响较小的体温节律记录表明，昼夜节律起搏器参与了昼夜节律类型的分化，因为在提供转轮后检测到的是短暂的同步化周期，而不是突然的相移。八齿鼠的昼行性似乎是多种机制的结果，这可能解释了不同过程如何导致相似的昼夜节律类型。
