Vera L M, López-Olmeda J F, Bayarri M J, Madrid J A, Sánchez-Vázquez F J
Department of Physiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Chronobiol Int. 2005;22(1):67-78. doi: 10.1081/cbi-200038157.
Melatonin production by the pineal organ is influenced by light intensity, as has been described in most vertebrate species, in which melatonin is considered a synchronizer of circadian rhythms. In tench, strict nocturnal activity rhythms have been described, although the role of melatonin has not been clarified. In this study we investigated daily activity and melatonin rhythms under 12:12 light-dark (LD) conditions with two different light intensities (58.6 and 1091 microW/cm2), and the effect of I h broad spectrum white light pulses of different intensities (3.3, 5.3, 10.5, 1091.4 microW/cm2) applied at middarkness (MD) on nocturnal circulating melatonin. The results showed that plasma melatonin in tench under LD 12:12 and high light conditions displayed rhythmic variation, where values at MD (255.8 +/- 65.9 pg/ml) were higher than at midlight (ML) (70.7 +/- 31.9 pg/ml). Such a difference between MD and ML values was reduced in animals exposed to LD 12: 12 and low light intensity. The application of 1 h light pulses at MD lowered plasma melatonin to 111.6 +/- 3.2 pg/ml (in the 3.3-10.5 microW/cm2 range) and to 61.8 +/- 18.3 pg/ml (with the 1091.4 microW/cm2 light pulse) and totally suppressed nocturnal locomotor activity. These results show that melatonin rhythms persisted in tench exposed to low light intensity although the amplitude of the rhythm is affected. In addition, it was observed that light pulses applied at MD affected plasma melatonin content and locomotor activity. Such a low threshold suggests that the melatonin system is capable of transducing light even under dim conditions, which may be used by this nocturnal fish to synchronize to weak night light signals (e.g., moonlight cycles).
松果体器官分泌褪黑素受光照强度影响，多数脊椎动物物种均如此，在这些物种中，褪黑素被视为昼夜节律的同步器。在丁鱥中，已描述了严格的夜间活动节律，不过褪黑素的作用尚未明确。在本研究中，我们调查了在12:12明暗（LD）条件下，两种不同光照强度（58.6和1091微瓦/平方厘米）下的日常活动和褪黑素节律，以及在午夜黑暗（MD）时施加不同强度（3.3、5.3、10.5、1091.4微瓦/平方厘米）的1小时广谱白光脉冲对夜间循环褪黑素的影响。结果表明，在12:12 LD和高光条件下，丁鱥血浆褪黑素呈现节律性变化，MD时的值（255.8±65.9皮克/毫升）高于中午光照（ML）时的值（70.7±31.9皮克/毫升）。在暴露于12:12 LD和低光照强度的动物中，MD和ML值之间的这种差异减小。在MD时施加1小时光脉冲可使血浆褪黑素降至111.6±3.2皮克/毫升（在3.3 - 10.5微瓦/平方厘米范围内）和61.8±18.3皮克/毫升（使用1091.4微瓦/平方厘米光脉冲时），并完全抑制夜间运动活动。这些结果表明，尽管节律幅度受到影响，但暴露于低光照强度下的丁鱥中褪黑素节律仍然存在。此外，观察到在MD时施加的光脉冲会影响血浆褪黑素含量和运动活动。如此低的阈值表明，即使在昏暗条件下，褪黑素系统也能够传导光线，这种夜行性鱼类可能利用这一点来与微弱的夜间光信号（如月光周期）同步。
