Iigo M, Hara M, Ohtani-Kaneko R, Hirata K, Tabata M, Aida K
Department of Anatomy, St. Marianna University School of Medicine, Kawasaki, Miyamae, Japan.
Biol Signals. 1997 Jul-Dec;6(4-6):225-32. doi: 10.1159/000109132.
Photic and circadian regulations of melatonin rhythms in the pineal organ and the retina of several teleosts were studied to investigate the regulatory mechanisms of melatonin rhythms in fishes. In the eyecup preparations of the goldfish, Carassius auratus, both time of day and lighting conditions affected melatonin production, with high melatonin production observed only in the dark-treated group incubated during the 'subjective' night. Thus, in the goldfish retina, local photoreceptors and an ocular circadian clock seem to regulate melatonin production, as in the zebrafish retina and in the pineal organ of a number of teleosts, including the goldfish. However, this circadian regulation of melatonin rhythms is not universal among fishes. Although the superfused pineal organ of the masu salmon Oncorhynchus masou secreted melatonin in a rhythmic fashion under light-dark (LD) cycles, the rhythm disappeared under constant darkness (DD), as in the rainbow trout, with a large amount of melatonin released both during the subjective day and the subjective night. These results suggest that all salmonids lack circadian regulation of melatonin rhythms. Furthermore, when ocular melatonin rhythms were compared in two cyprinids, the ugui Tribolodon hakonensis and the oikawa Zacco platypus occupying different ecological niches, ocular melatonin contents exhibited daily variations, with higher values during the dark phase of LD cycles in both species. The rhythmic changes persisted in the ugui under DD, with higher levels at subjective midnight than at subjective midday; however, ocular melatonin levels in the oikawa were consistently high under DD. Thus, the circadian regulation of melatonin rhythms in fishes is influenced not only by phylogeny, but also by the ecological niches of the animals. These results suggest that the physiological functions of melatonin in the circadian and photoperiodic systems differ among fishes.
为了研究鱼类褪黑素节律的调节机制，对几种硬骨鱼松果体器官和视网膜中褪黑素节律的光调节和昼夜节律调节进行了研究。在金鱼（Carassius auratus）的眼杯制备物中，一天中的时间和光照条件都会影响褪黑素的产生，只有在“主观”夜间孵育的黑暗处理组中观察到高褪黑素产生。因此，在金鱼视网膜中，局部光感受器和眼内生物钟似乎像在斑马鱼视网膜以及包括金鱼在内的许多硬骨鱼的松果体器官中一样调节褪黑素的产生。然而，褪黑素节律的这种昼夜节律调节在鱼类中并不普遍。尽管马苏大麻哈鱼（Oncorhynchus masou）的离体松果体器官在明暗（LD）循环下以节律性方式分泌褪黑素，但与虹鳟鱼一样，在持续黑暗（DD）条件下该节律消失，在主观白天和主观夜间都会释放大量褪黑素。这些结果表明，所有鲑科鱼类都缺乏褪黑素节律的昼夜节律调节。此外，当比较两种鲤科鱼类——占据不同生态位的日本七鳃鳗（Tribolodon hakonensis）和宽鳍鱲（Zacco platypus）的眼内褪黑素节律时，眼内褪黑素含量呈现出每日变化，在两种鱼类的LD循环黑暗期含量都较高。在DD条件下，日本七鳃鳗的节律变化持续存在，主观午夜时的水平高于主观中午；然而，宽鳍鱲的眼内褪黑素水平在DD条件下一直很高。因此，鱼类褪黑素节律的昼夜节律调节不仅受系统发育的影响，还受动物生态位的影响。这些结果表明，褪黑素在昼夜节律和光周期系统中的生理功能在鱼类中有所不同。
