Entrainment of the circadian clock by daily ambient temperature cycles in the camel (Camelus dromedarius)
Entrainment of the circadian clock by daily ambient temperature cycles in the camel (Camelus dromedarius)
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DOI：
10.1152/ajpregu.00466.2012
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发表时间：
2013-06-01
影响因子：
2.8
通讯作者：
Pevet, Paul
中科院分区：
文献类型：
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作者：
El Allali, Khalid;Achaaban, Mohamed R.;Pevet, Paul
在哺乳动物中，光-暗(LD)周期被认为是同步生物钟的主要线索。在干旱和沙漠地区，骆驼(Camelus Dromedarius)暴露在极端环境条件下。由于环境温度(T-a)的大范围波动是这种环境中的一个主要因素，我们想知道周期性的T-a波动是否有助于昼夜节律的同步。选择体温节律(T-b)作为生物钟的输出。在验证了T-b被LD同步并在连续黑暗(DD)中自由奔跑后，我们让动物在LL和DD中进行T-a的每日循环。在这两种情况下，T-b节律都被牵连到T-a周期。在T-a周期的12小时相移中，T-b周期的平均相移范围从LD的几小时(余弦法1h，曲线峰的4h)到LL的7-8h和DD的12h。这些结果可能反映了T-a每日周期对中枢时钟的真正同步，也可能反映了T-a对T-b的被动影响。为了解决模糊性，褪黑素的节律性被用作时钟的另一个输出。在DD中，褪黑激素的节律也被T-a周期所缠绕，证明每天的T-a周期能够缠绕骆驼的生物钟，类似于光周期。相比之下，在存在LD周期的情况下，7只骆驼中只有2只(或3只)的褪黑激素的节律被T-a周期改变：在这些特定的条件下，T-a对时钟的系统性影响不能被证明。总而言之，根据实验条件(DD和LD)，每日T-a周期既可以起到时代激进剂的作用，也可以不起作用。
In mammals the light-dark (LD) cycle is known to be the major cue to synchronize the circadian clock. In arid and desert areas, the camel (Camelus dromedarius) is exposed to extreme environmental conditions. Since wide oscillations of ambient temperature (T-a) are a major factor in this environment, we wondered whether cyclic T-a fluctuations might contribute to synchronization of circadian rhythms. The rhythm of body temperature (T-b) was selected as output of the circadian clock. After having verified that T-b is synchronized by the LD and free runs in continuous darkness (DD), we submitted the animals to daily cycles of T-a in LL and in DD. In both cases, the T-b rhythm was entrained to the cycle of T-a. On a 12-h phase shift of the T-a cycle, the mean phase shift of the T-b cycle ranged from a few hours in LD (1 h by cosinor, 4 h from curve peaks) to 7-8 h in LL and 12 h in DD. These results may reflect either true synchronization of the central clock by T-a daily cycles or possibly a passive effect of T-a on T-b. To resolve the ambiguity, melatonin rhythmicity was used as another output of the clock. In DD melatonin rhythms were also entrained by the T-a cycle, proving that the daily T-a cycle is able to entrain the circadian clock of the camel similar to photoperiod. By contrast, in the presence of a LD cycle the rhythm of melatonin was modified by the T-a cycle in only 2 (or 3) of 7 camels: in these specific conditions a systematic effect of T-a on the clock could not be evidenced. In conclusion, depending on the experimental conditions (DD vs. LD), the daily T-a cycle can either act as a zeitgeber or not.