Grosse J, Hastings M H
Department of Anatomy, University of Cambridge, United Kingdom.
J Biol Rhythms. 1996 Dec;11(4):317-24. doi: 10.1177/074873049601100405.
Seasonal rhythms of reproduction in the Syrian hamster are triggered by the pineal hormone melatonin. By varying the parameters of systemic infusions of exogenous melatonin delivered to pinealectomized hamsters, it has been shown that the hypothalamus is sensitive to the duration of individual signals, which serve as an inverse coding of day length. It also has been shown that animals are sensitive to the temporal structure of a series of signals insofar as a series of melatonin infusions of appropriate number and duration may fail to invoke a gonadal response if they are presented at inappropriate frequencies. Although the endogenous circadian pacemaker of the suprachiasmatic nucleus (SCN) is not thought to be involved in the measurement of or response to melatonin signal duration, its contribution to the interpretation of a series of melatonin signals remains to be determined. Syrian hamsters are able to show a short-day-like gonadal response to a series of melatonin signals delivered on a variety of noncircadian schedules, including one in which a "random" pattern of infusions is employed. This study investigated the role of the SCN in the interpretation of such infusion paradigms. Adult male Syrian hamsters received electrolytic lesions of the SCN. Pinealectomized, lesioned, and intact hamsters then were infused with melatonin or saline at one of three different phases of the day in a random pattern such that no signal was predictive of the timing of the next. Other lesioned and intact animals received melatonin or saline at the same time daily. After 6 weeks, control saline-infused animals in both lesioned and intact groups had large testes. However, sham animals receiving melatonin in the random infusion pattern had regressed testes, as did the lesioned animals receiving melatonin at the same phase every day. By contrast, lesioned animals that received melatonin in the random pattern of infusion did not show a short-day gonadal response. These results suggest that although the SCN is not necessary for measurement of the duration of individual signals, it may play a role in the interpretation of a series of melatonin signals in which the number of melatonin signals and the period of time over which they are encountered need to be compared.
叙利亚仓鼠繁殖的季节性节律由松果体激素褪黑素触发。通过改变给予松果体切除的仓鼠外源性褪黑素全身输注的参数，已表明下丘脑对单个信号的持续时间敏感，这些信号作为日长的反向编码。还表明，动物对一系列信号的时间结构敏感，因为如果以不适当的频率呈现，一系列数量和持续时间合适的褪黑素输注可能无法引发性腺反应。尽管视交叉上核（SCN）的内源性昼夜节律起搏器不被认为参与褪黑素信号持续时间的测量或反应，但其对一系列褪黑素信号解释的贡献仍有待确定。叙利亚仓鼠能够对以各种非昼夜节律时间表传递的一系列褪黑素信号表现出类似短日照的性腺反应，包括采用“随机”输注模式的情况。本研究调查了SCN在解释此类输注模式中的作用。成年雄性叙利亚仓鼠接受了SCN的电解损伤。然后，松果体切除、损伤和完整的仓鼠在一天的三个不同阶段之一以随机模式输注褪黑素或生理盐水，使得没有信号能够预测下一个信号的时间。其他损伤和完整的动物每天在同一时间接受褪黑素或生理盐水。6周后，损伤组和完整组中接受生理盐水输注的对照动物睾丸较大。然而，以随机输注模式接受褪黑素的假手术动物睾丸萎缩，每天在同一阶段接受褪黑素的损伤动物也是如此。相比之下，以随机输注模式接受褪黑素的损伤动物没有表现出类似短日照的性腺反应。这些结果表明，虽然SCN对于单个信号持续时间的测量不是必需的，但它可能在解释一系列褪黑素信号中发挥作用，在这些信号中，需要比较褪黑素信号的数量和遇到它们的时间段。
