Effects of Magnetic Fields on Biological Clock Generating Circadian Rhythm

有研究表明，50Hz磁场可抑制松果体夜间褪黑激素的分泌。支配松果体的交感神经元由生物钟的内在活动驱动，称为视交叉上核（SCN）。本研究首次尝试研究50Hz磁场暴露对SCN自身产生的昼夜节律是否有影响。磁场暴露的线圈系统，三组四方形梅里特线圈相互垂直组合，放置在一个磁和电磁屏蔽室。将玻璃涂层双极金属微电极立体定位插入乌拉坦麻醉的大鼠SCN中，以测量SCN的细胞外活性，将大鼠置于屏蔽室中，将其头部水平固定在线圈系统的中心。在整个实验过程中，大鼠保持在黑暗和安静的条件下。将大鼠分为四组，一组为对照组，三组为实验组。对照组大鼠在实验过程中暴露于40 μ T向下的静磁场。实验大鼠暴露于50Hz、峰峰值为40 μ T的正弦磁场中，磁场分别沿着垂直轴（z轴）、平行于头部纵轴（x轴）或垂直于水平面x轴（y轴），外加向下的静磁场。连续记录SCN细胞外活性超过60小时，对照组SCN活性出现明显的昼夜节律。50 Hz磁场沿着z轴暴露大鼠的SCN活性呈现与对照组相似的昼夜节律，而50 Hz磁场沿着x轴或y轴暴露大鼠的SCN活性的昼夜节律明显紊乱。

Some reports have shown that the5O Hz magnetic field could suppress the nocturnal melatonin secretion in the pineal gland. The sympathetic neurons that innervate the pineal gland are driven by the intrinsic activity of the biological clock, known as the suprachiasmatic nucleus (SCN). The study reported here is the first attempt to investigate whether the 50Hz magnetic field exposure have any effects on the circadian rhythm generated in SCN itself.Wister rats were employed in the experiments. The coil system for magnetic field exposure, three sets of four-square Merritt coils combined perpendicularly one another, was placed in a magnetically and electromagnetically shielded room. A glass-coated bipolar metal microelectrode was inserted stereotaxically into the SCN of a rat anesthetized with Urethane in order to measure the extracellular activity of SCN, and the rat was put into the shielded room and its head was fixed horizontally at the center of the coil system. The rat was kept in the dark and silent condition throughout the experiment. Rats were divided into four groups, one control and three experimentalgroups. The control rats were exposed with 40 muT static magnetic field directing downward during the experiments. The experimental rats were exposed with 50Hz, peak-to-peak of 40 muT, sinusoidal magnetic field along the vertical axis (z-axis), parallel to the longitudinal axis of the head (x-axis) or perpendicular to x-axis in horizontal plane (y-axis) respectively added to the downward static magnetic field. The extracellular activity of SCN was recorded for more than 60 hours.Clear circadian rhythm appeared in the SCN activity of the control rat. The SCN activity of the rat exposed with the 50Hz magnetic field along z-axis showed circadian rhythm similar way to the control, whereas the remarkable disorder of the circadian rhythm of SCN activity was observed when the rat was exposed with the 50 Hz magnetic field along x-axis or y-axis.