Silver R, LeSauter J
Barnard College of Columbia University, New York, New York 10027.
J Biol Rhythms. 1993;8 Suppl:S89-92.
It is well established that the mammalian suprachiasmatic nucleus (SCN) is a biological pacemaker that entrains the activity of organisms to their environment and controls circadian rhythmicity. However, neither the nature of these coupling signal or signals from the SCN, nor their target or targets in the brain, are well understood. Fiber efferents from the SCN reach nearby hypothalamic regions, suggesting a coupling role for neural efferent pathways. The SCN produces diffusible signals that reach nearby hypothalamic sites and the cerebrospinal fluid, suggesting a role for a diffusible efferent pathway. We consider the possibility of redundant coupling signals of the SCN, and review evidence suggesting that diffusible elements may be sufficient to sustain locomotor rhythmicity in adult animals and to restore locomotor rhythmicity in lesioned hamsters bearing SCN grafts. We also provide data for the occurrence of signals that synchronize oscillators, regardless of initial phase. The distinct role of neural and diffusible SCN coupling signals, and the role of SCN-driven rhythmic systems (pineal melatonin rhythms, body temperature), remain to be explored.
哺乳动物的视交叉上核（SCN）作为生物起搏器，使生物体的活动与环境同步并控制昼夜节律，这一点已得到充分证实。然而，这些来自SCN的耦合信号的性质、它们在大脑中的一个或多个靶点，都尚未被完全理解。SCN的纤维传出神经到达附近的下丘脑区域，这表明神经传出通路具有耦合作用。SCN产生可扩散信号，这些信号到达附近的下丘脑部位和脑脊液，这表明存在一条可扩散的传出通路。我们考虑了SCN冗余耦合信号的可能性，并回顾了相关证据，这些证据表明可扩散成分可能足以维持成年动物的运动节律，并恢复带有SCN移植体的损伤仓鼠的运动节律。我们还提供了关于同步振荡器信号出现的数据，无论其初始相位如何。神经和可扩散的SCN耦合信号的独特作用，以及SCN驱动的节律系统（松果体褪黑素节律、体温）的作用，仍有待探索。
