Kanematsu N
Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
Hokkaido Igaku Zasshi. 1994 Jan;69(1):46-64.
Light has dual effects on the pineal melatonin; one is the entrainment of the circadian rhythm and the other is suppression of the melatonin synthesis. It is not known whether the entraining and suppressing effects of light are mediated by the same pathway or not. To elucidate the mechanism of the dual effects of light, (1) the sensitivity of the retina, (2) effects of acetylcholine agonist and, (3) the arrhythmicity induced by longterm continuous light, were studied by measuring melatonin continuously from a single rat by means of in vivo microdialysis. Pineal melatonin was suppressed by light more strongly at the late dark phase than at midnight, and by green light (520nm) than by red light (660nm). Pineal melatonin measured by microdialysis was decreased rapidly by a short light exposure and the melatonin rhythm was shifted on the following days. Microinjection of cholinergic agonist, carbachol, into the suprachiasmatic nucleus neither suppressed nor entrained the pineal melatonin rhythm. Immediately after the blinding, rats showed the circadian rhythm in pineal melatonin which had been abolished under long-term continuous light. While, it took several days for the locomotor rhythm to reappear. It is concluded that, (1) suppression of the pineal melatonin by light depends on the circadian phase and on the wavelength of light, (2) the threshold for light suppression is lower than that for phase-shift, (3) the melatonin rhythm starts to phase-shift on the following day of light pulse. (4) Acetylcholine is unlikely to be involved in the photic transmission both to the circadian clock and to the pineal, (5) arrhythmicity induced by long-term continuous light seems to be due to masking for the melatonin rhythm, and to uncoupling from the clock for the locomotor rhythm.
一是对昼夜节律的同步作用，另一是对褪黑素合成的抑制作用。目前尚不清楚光的同步和抑制作用是否通过相同途径介导。为阐明光的双重作用机制，通过体内微透析法对单只大鼠连续测量褪黑素，研究了(1)视网膜的敏感性、(2)乙酰胆碱激动剂的作用以及(3)长期持续光照诱导的节律紊乱。在黑暗后期，松果体褪黑素受光抑制的程度比午夜时更强，且绿光(520nm)比红光(660nm)的抑制作用更强。通过微透析测量的松果体褪黑素在短时间光照下迅速降低，且在随后几天褪黑素节律发生了改变。向视交叉上核微量注射胆碱能激动剂卡巴胆碱，既不抑制也不同步松果体褪黑素节律。致盲后，大鼠松果体褪黑素立即呈现昼夜节律，而在长期持续光照下该节律已消失。然而，运动节律的重新出现需要数天时间。研究得出以下结论：(1)光对松果体褪黑素的抑制作用取决于昼夜节律相位和光的波长；(2)光抑制的阈值低于相位移动的阈值；(3)褪黑素节律在光脉冲后的第二天开始发生相位移动；(4)乙酰胆碱不太可能参与向昼夜节律时钟和松果体的光信号传递；(5)长期持续光照诱导的节律紊乱似乎是由于对褪黑素节律的掩盖以及与运动节律时钟的解耦。
