The orexinergic system delivers excitation for multiple brain centers to facilitate behavioral arousal, with its malfunction resulting in narcolepsy, somnolence, and notably, visual hallucinations. Since the circadian clock underlies the daily arousal, a timed coordination is expected between the orexin system and its target subcortical visual system, including the superior colliculus (SC). Here, we use a combination of electrophysiological, immunohistochemical, and molecular approaches across 24 h, together with the neuronal tract-tracing methods to investigate the daily coordination between the orexin system and the rodent SC. Higher orexinergic input was found to occur nocturnally in the superficial layers of the SC, in time for nocturnal silencing of spontaneous firing in this visual brain area. We identify autonomous daily and circadian expression of clock genes in the SC, which may underlie these day–night changes. Additionally, we establish the lateral hypothalamic origin of the orexin innervation to the SC and that the SC neurons robustly respond to orexin A via OX₂ receptor in both excitatory and GABA_A receptor-dependent inhibitory manners. Together, our evidence elucidates the combination of intrinsic and extrinsic clock mechanisms that shape the daily function of the visual layers of the SC.

中文翻译：

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大鼠上丘中食欲门控的日常协调——对视觉系统内在时钟活动的影响

食欲系统为多个大脑中枢提供兴奋以促进行为唤醒，其故障会导致发作性睡病、嗜睡，尤其是视觉幻觉。由于生物钟是每日唤醒的基础，因此预计食欲素系统与其目标皮层下视觉系统（包括上丘 (SC)）之间会出现定时协调。在这里，我们在 24 小时内结合使用电生理学、免疫组织化学和分子方法，以及神经元束追踪方法来研究食欲素系统和啮齿动物 SC 之间的日常协调。发现更高的食欲输入在夜间发生在 SC 的浅层，及时在这个视觉大脑区域夜间沉默自发性放电。我们确定了 SC 中时钟基因的自主日常和昼夜节律表达，这可能是这些昼夜变化的基础。此外，我们确定了对 SC 的食欲素神经支配的外侧下丘脑起源，并且 SC 神经元通过 OX 对食欲素 A 做出强烈反应₂受体以兴奋性和 GABA _A受体依赖性抑制方式。总之，我们的证据阐明了塑造 SC 视觉层日常功能的内在和外在时钟机制的组合。