Sumová A, Illnerová H
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
Am J Physiol. 1998 Mar;274(3):R857-63. doi: 10.1152/ajpregu.1998.274.3.R857.
To date, photic entrainment of the mammalian circadian system has been studied by following phase shifts of overt rhythms in the periphery governed by a circadian pacemaker located in the suprachiasmatic nucleus (SCN). The present study follows for the first time photic resetting of intrinsic rhythmicity of the SCN itself. Rats maintained under either a shorter photoperiod, with 12 h of light and 12 h of darkness per day, or under a long, 18:6-h light-dark photoperiod were exposed to a light stimulus during the dark period and then released into darkness, and the next day the SCN rhythm in the light-stimulated c-Fos protein immunoreactivity was followed as a marker of the SCN endogenous rhythmicity. After a light stimulus in the early night, the evening rise in the photic elevation of Fos protein photoinduction as well as the morning decline were phase delayed within one cycle. After a light stimulus in the late night, only the morning decline in the photic elevation of Fos was phase advanced the next night, not the evening rise; consequently, the interval enabling high photic elevation of Fos was reduced. After a light stimulus was administered around the middle of the night, the next night the evening rise in the light-stimulated Fos was eventually phase delayed, the morning decline was phase advanced, and the rhythm amplitude was reduced significantly; under 18:6-h light-dark, a mere 5-min light exposure exhibited such effects. The data indicate that resetting of the SCN rhythmicity in the light-elevated c-Fos 1 day after a resetting stimulus administration, i.e., during transient cycles, may proceed via nonparallel phase shifts of the evening rise and of the morning decline of the light-stimulated Fos, and via amplitude lowering and suggest a complex circadian pacemaking system in the rat SCN.
迄今为止，通过追踪位于视交叉上核（SCN）的昼夜节律起搏器所调控的外周明显节律的相位变化，对哺乳动物昼夜节律系统的光诱导进行了研究。本研究首次追踪了SCN自身内在节律性的光重置。将大鼠分别维持在较短的光周期（每天12小时光照和12小时黑暗）或较长的18:6小时光暗光周期下，在黑暗期给予光刺激，然后置于黑暗中，次日追踪光刺激后的c-Fos蛋白免疫反应性中的SCN节律，以此作为SCN内源性节律性的标志物。在深夜给予光刺激后，Fos蛋白光诱导的光升高的傍晚上升以及早晨下降在一个周期内均出现相位延迟。在深夜给予光刺激后，仅Fos光升高的早晨下降在次日夜间出现相位提前，而傍晚上升未出现；因此，使Fos产生高光诱导的间隔缩短。在午夜前后给予光刺激后，次日夜间光刺激的Fos的傍晚上升最终出现相位延迟，早晨下降出现相位提前，且节律幅度显著降低；在18:6小时光暗条件下，仅5分钟的光照就表现出这种效应。数据表明，在给予重置刺激1天后，即在短暂周期期间，光升高的c-Fos中SCN节律性的重置可能通过光刺激的Fos的傍晚上升和早晨下降的非平行相位变化以及幅度降低来进行，这提示大鼠SCN中存在一个复杂的昼夜节律起搏系统。
