Iigo Masayuki, Sato Masaru, Ikeda Emi, Kawasaki Shigekatsu, Noguchi Fumitaka, Nishi Genjirou
Department of Anatomy, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-ku, Kawasaki 216-8511, Japan.
Gen Comp Endocrinol. 2003 Sep;133(2):252-9. doi: 10.1016/s0016-6480(03)00168-0.
The wrasse Halichoeres tenuispinnis is a labrid teleost that exhibits robust circadian rhythms in locomotor activity under constant light (LL). This fish buries itself in the bottom sand during the subjective-night, thereby suggesting that behaviorally it adjusts its circadian clock to avoid photoreception. In this study, we determined ocular melatonin contents of the wrasse under various photic environments and used ocular melatonin to indicate photoreception. Under light-dark (LD) cycles, ocular melatonin contents of the wrasse exhibited a daily rhythm, with higher levels during the dark phase than those during the light phase. The duration of nocturnal melatonin elevation was longer under LD 9:15 than under LD 15:9. Acute exposure to 2-h light during the dark phase resulted in a significant decrease in ocular melatonin at mid-dark in an intensity-dependent manner. However, acute exposure to different intensities of light for 2h during the light phase had only a small effect on ocular melatonin contents at mid-day. Under LL, ocular melatonin contents in the wrasse reared with bottom sand present exhibited circadian rhythms and were significantly higher than those with transluscent acryl pellets on the bottom. These results indicate that the ocular melatonin rhythm in the wrasse is driven both by the photic environment and by a circadian clock, and that the wrasse that buries itself in the bottom sand can perceive low intensity of light.
细棘海猪鱼是一种隆头鱼科硬骨鱼，在持续光照（LL）条件下其运动活动表现出强烈的昼夜节律。这种鱼在主观夜间会将自己埋入底沙中，这表明在行为上它会调整其生物钟以避免光接收。在本研究中，我们测定了该海猪鱼在各种光照环境下的眼部褪黑素含量，并使用眼部褪黑素作为光接收的指标。在明暗（LD）循环条件下，海猪鱼的眼部褪黑素含量呈现出每日节律，黑暗期的含量高于光照期。在LD 9:15条件下夜间褪黑素升高的持续时间比在LD 15:9条件下更长。在黑暗期急性暴露于2小时光照会导致黑暗中期眼部褪黑素显著下降，且呈强度依赖性。然而，在光照期急性暴露于不同强度的光照2小时对中午时的眼部褪黑素含量影响较小。在LL条件下，饲养时有底沙的海猪鱼的眼部褪黑素含量呈现出昼夜节律，且显著高于底部有半透明丙烯酸小球的海猪鱼。这些结果表明，海猪鱼的眼部褪黑素节律受光照环境和生物钟共同驱动，并且埋入底沙中的海猪鱼能够感知低强度的光。
