Harry S. Truman Memorial Veterans Hospital and Department of Neurology, University of Missouri-School of Medicine, Columbia, MO, USA.
J Pineal Res. 2018 Sep;65(2):e12498. doi: 10.1111/jpi.12498. Epub 2018 May 7.
Melatonin promotes sleep. However, the underlying mechanisms are unknown. Orexin neurons in the perifornical lateral hypothalamus (PFH) are pivotal for wake promotion. Does melatonin promote sleep by inhibiting orexin neurons? We used C57BL/6J mice and designed 4 experiments to address this question. Experiment 1 used double-labeled immunofluorescence and examined the presence of melatonin receptors on orexin neurons. Second, mice, implanted with bilateral guides targeted toward PFH and sleep-recording electrodes, were infused with melatonin (500 pmole/50 nL/side) at dark onset (onset of active period), and spontaneous bouts of sleep-wakefulness were examined. Third, mice, implanted with bilateral guides into the PFH, were infused with melatonin (500 pmole/50 nL/side) at dark onset and euthanized 2 hours later, to examine the activation of orexin neurons using c-Fos expression in orexin neurons. Fourth, mice, implanted with PFH bilateral guides and sleep-recording electrodes, were infused with melatonin receptor antagonist, luzindole (10 pmol/50 nL/side), at light onset (onset of sleep period), and spontaneous bouts of sleep-wakefulness were examined. Our results suggest that orexin neurons express MT1, but not MT2 receptors. Melatonin infusion into the PFH, at dark onset, site-specifically and significantly increased NREM sleep (43.7%, P = .003) and reduced wakefulness (12.3%, P = .013). Local melatonin infusion at dark onset inhibited orexin neurons as evident by a significant reduction (66%, P = .0004) in the number of orexin neurons expressing c-Fos. Finally, luzindole infusion-induced blockade of melatonin receptors in PFH at sleep onset significantly increased wakefulness (44.1%, P = .015). Based on these results, we suggest that melatonin may act via the MT1 receptors to inhibit orexin neurons and promote sleep.
褪黑素促进睡眠。然而，其潜在机制尚不清楚。外侧下丘脑穹窿周（PFH）中的食欲素神经元对于促进觉醒至关重要。褪黑素是否通过抑制食欲素神经元来促进睡眠？我们使用 C57BL/6J 小鼠设计了 4 项实验来解决这个问题。实验 1 使用双标记免疫荧光法，检测食欲素神经元上是否存在褪黑素受体。其次，将双侧导向器植入 PFH 并植入睡眠记录电极的小鼠，在暗期开始时（活动期开始时）给予褪黑素（500pmole/50nL/侧）输注，并检查自发的睡眠-觉醒发作。第三，将双侧导向器植入 PFH 的小鼠在暗期开始时给予褪黑素（500pmole/50nL/侧）输注，2 小时后处死，使用 c-Fos 表达检测食欲素神经元的激活。第四，将双侧 PFH 导向器和睡眠记录电极植入的小鼠，在光照开始时（睡眠期开始时）给予褪黑素受体拮抗剂，鲁米诺（10pmol/50nL/侧），并检查自发的睡眠-觉醒发作。我们的结果表明，食欲素神经元表达 MT1，但不表达 MT2 受体。在暗期开始时将褪黑素输注到 PFH 中，可特异性且显著增加非快速动眼睡眠（43.7%，P=.003）并减少觉醒（12.3%，P=.013）。在暗期开始时在 PFH 局部给予褪黑素可抑制食欲素神经元，这表现在表达 c-Fos 的食欲素神经元数量明显减少（66%，P=.0004）。最后，在睡眠开始时在 PFH 中注入鲁米诺诱导的褪黑素受体阻断显著增加了觉醒（44.1%，P=.015）。基于这些结果，我们认为褪黑素可能通过 MT1 受体抑制食欲素神经元并促进睡眠。
