Scheer F A J L, Pirovano C, Van Someren E J W, Buijs R M
Department of Hypothalamic Integration Mechanisms, Netherlands Institute for Brain Research, Amsterdam, The Netherlands.
Neuroscience. 2005;132(2):465-77. doi: 10.1016/j.neuroscience.2004.12.012.
The mammalian biological clock, located in the suprachiasmatic nucleus (SCN), is crucial for circadian rhythms in physiology and behavior. However, equivocal findings have been reported on its role in the circadian regulation of body temperature. The goal of the present studies was to investigate the interaction between the SCN and environmental light in the regulation of body temperature. All recordings were performed by telemetry in free moving male Wistar rats. Firstly, we demonstrated an endogenous circadian rhythm in body temperature independent of locomotor activity. This rhythm was abolished by stereotactic lesioning of the SCN. Secondly, we demonstrated a circadian phase-dependent suppressive effect of light ('negative masking') on body temperature. Light suppressed body temperature more at the end of the subjective night (circadian time [CT] 22) than in the middle (CT 6) and at the end (CT 10) of the subjective day. This circadian-phase dependent suppression was not demonstrated in SCN-lesioned animals. Surprisingly, after half a year of recovery from lesioning of the SCN, light regained its suppressing action on body temperature, resulting in a daily body temperature rhythm only under light-dark conditions. In contrast to body temperature, light could not substantially mimic a daytime inhibitory SCN-output in the regulation of heart rate and locomotor activity. The present results suggest that, after lesioning of the SCN as main relay station for the immediate body temperature-inhibition by light, secondary relay nuclei can fully take over this function of the SCN. These findings provide a possible explanation for the controversy in literature over the question whether the SCN is required for the diurnal rhythm in body temperature. Furthermore, they show that light may have an acute effect on behavior and physiology of the organism via the SCN, which extends beyond the generally acknowledged effect on melatonin secretion.
位于视交叉上核（SCN）的哺乳动物生物钟对于生理和行为的昼夜节律至关重要。然而，关于其在体温昼夜调节中的作用，已有相互矛盾的研究结果报道。本研究的目的是探讨SCN与环境光在体温调节中的相互作用。所有记录均通过遥测技术在自由活动的雄性Wistar大鼠中进行。首先，我们证明了体温存在独立于运动活动的内源性昼夜节律。这种节律通过SCN的立体定向损伤而被消除。其次，我们证明了光对体温具有昼夜相依赖性抑制作用（“负性掩盖”）。在主观夜间结束时（昼夜时间[CT]22），光对体温的抑制作用比在主观白天的中间（CT6）和结束时（CT10）更强。在SCN损伤的动物中未观察到这种昼夜相依赖性抑制作用。令人惊讶的是，在SCN损伤半年恢复后，光恢复了其对体温的抑制作用，导致仅在明暗条件下出现每日体温节律。与体温不同，在心率和运动活动的调节中，光不能充分模拟白天抑制性的SCN输出。目前的结果表明，作为光对体温直接抑制作用的主要中继站，SCN损伤后，次级中继核可以完全接管SCN的这一功能。这些发现为文献中关于体温昼夜节律是否需要SCN的争议提供了一种可能的解释。此外，它们表明光可能通过SCN对生物体的行为和生理产生急性影响，这超出了普遍认可的对褪黑素分泌的影响。
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