Underwood H, Calaban M
Department of Zoology, North Carolina State University, Raleigh 27695.
J Biol Rhythms. 1987 Fall;2(3):179-93. doi: 10.1177/074873048700200302.
Both light and temperature can influence the pineal's synthesis of the indoleamine melatonin. An investigation of the effects of light and temperature cycles on the pineal melatonin rhythm (PMR) showed the following: (1) Both daily light cycles and daily temperature cycles could entrain the PMR; melatonin levels peaked during the dark phase of a light-dark cycle or the cool phase of a temperature cycle. (2) The PMR could be entrained by a temperature cycle as low as 2 degrees C in amplitude in lizards held in constant light or constant darkness. (3) The length of the photoperiod or thermoperiod affected the phase, amplitude, or duration of the PMR. (4) When presented together, the effects of light and temperature cycles on the PMR depended on the phase relationship between the light and temperature cycles, as well as on the strength of the entraining stimuli, such as the amplitude of the temperature cycle. (5) Exposure to a constant cold temperature (10 degrees C) eliminated the PMR, yet a rhythm could still be expressed under a 24-hr temperature cycle (32 degrees C/10 degrees C), and the rhythm peaked during the 10 degrees C phase of the cycle. (6) A 6-hr dark pulse presented during the day did not elicit a premature rise in melatonin levels. These studies show how environmental stimuli can control the pineal rhythm of melatonin synthesis and secretion. Previous studies have supported a model in which the lizard's pineal acts as a circadian pacemaker within a multioscillator circadian system, and have implicated melatonin as a hormone by which the pineal may communicate with the rest of the system. The lizard pineal, therefore, may act as a photo- and thermoendocrine transducer translating light and temperature information into an internal cue in the form of the PMR. The PMR, in turn, may control the phase and period of circadian clocks located elsewhere, insuring that the right internal events occur at the right time of day.
光和温度都能影响松果体中吲哚胺褪黑素的合成。一项关于光和温度周期对松果体褪黑素节律（PMR）影响的研究表明：（1）每日的光周期和温度周期都能使PMR同步；褪黑素水平在明暗周期的黑暗阶段或温度周期的凉爽阶段达到峰值。（2）在持续光照或持续黑暗条件下饲养的蜥蜴中，低至2摄氏度振幅的温度周期就能使PMR同步。（3）光周期或热周期的长度会影响PMR的相位、振幅或持续时间。（4）当光和温度周期同时存在时，它们对PMR的影响取决于光周期和温度周期之间的相位关系，以及同步刺激的强度，如温度周期的振幅。（5）暴露于恒定低温（10摄氏度）会消除PMR，但在24小时温度周期（32摄氏度/10摄氏度）下仍能表现出节律，且节律在周期的10摄氏度阶段达到峰值。（6）白天出现的6小时黑暗脉冲不会引发褪黑素水平过早升高。这些研究表明环境刺激如何控制松果体褪黑素合成和分泌的节律。先前的研究支持一种模型，即蜥蜴的松果体在多振荡器昼夜节律系统中充当昼夜节律起搏器，并认为褪黑素是松果体可能与系统其他部分进行通信的一种激素。因此，蜥蜴的松果体可能充当光和热内分泌转换器，将光和温度信息转化为PMR形式的内部信号。反过来，PMR可能控制位于其他地方的昼夜节律时钟的相位和周期，确保正确的内部事件在一天中的正确时间发生。
