Apergis-Schoute John, Iordanidou Panagiota, Faure Cedric, Jego Sonia, Schöne Cornelia, Aitta-Aho Teemu, Adamantidis Antoine, Burdakov Denis
Department of Pharmacology, University of Cambridge, Cambridge, CB2 1PD, United Kingdom,
Division of Neurophysiology, MRC National Institute for Medical Research, London NW7 1AA, United Kingdom.
J Neurosci. 2015 Apr 8;35(14):5435-41. doi: 10.1523/JNEUROSCI.5269-14.2015.
The lateral hypothalamus (LH) is a key regulator of multiple vital behaviors. The firing of brain-wide-projecting LH neurons releases neuropeptides promoting wakefulness (orexin/hypocretin; OH), or sleep (melanin-concentrating hormone; MCH). OH neurons, which coexpress glutamate and dynorphin, have been proposed to excite their neighbors, including MCH neurons, suggesting that LH may sometimes coengage its antagonistic outputs. However, it remains unclear if, when, and how OH actions promote temporal separation of the sleep and wake signals, a process that fails in narcolepsy caused by OH loss. To explore this directly, we paired optogenetic stimulation of OH cells (at rates that promoted awakening in vivo) with electrical monitoring of MCH cells in mouse brain slices. Membrane potential recordings showed that OH cell firing inhibited action potential firing in most MCH neurons, an effect that required GABAA but not dynorphin receptors. Membrane current analysis showed that OH cell firing increased the frequency of fast GABAergic currents in MCH cells, an effect blocked by antagonists of OH but not dynorphin or glutamate receptors, and mimicked by bath-applied OH peptide. In turn, neural network imaging with a calcium indicator genetically targeted to MCH neurons showed that excitation by bath-applied OH peptides occurs in a minority of MCH cells. Collectively, our data provide functional microcircuit evidence that intra-LH feedforward loops may facilitate appropriate switching between sleep and wake signals, potentially preventing sleep disorders.
外侧下丘脑（LH）是多种重要行为的关键调节因子。投射至全脑的LH神经元放电会释放促进清醒的神经肽（食欲素/下丘脑泌素；OH）或促进睡眠的神经肽（促黑素细胞激素；MCH）。有人提出，共表达谷氨酸和强啡肽的OH神经元会兴奋其相邻神经元，包括MCH神经元，这表明LH有时可能会同时激活其相互拮抗的输出。然而，OH的作用是否、何时以及如何促进睡眠和清醒信号的时间分离仍不清楚，而在由OH缺失引起的发作性睡病中，这一过程会失败。为了直接探究这一问题，我们将对OH细胞的光遗传学刺激（以促进体内觉醒的频率）与对小鼠脑片上MCH细胞的电监测相结合。膜电位记录显示，OH细胞放电抑制了大多数MCH神经元的动作电位发放，这种效应需要GABAA受体而非强啡肽受体。膜电流分析表明，OH细胞放电增加了MCH细胞中快速GABA能电流的频率，这种效应可被OH拮抗剂阻断，但不能被强啡肽或谷氨酸受体拮抗剂阻断，并可被浴加OH肽模拟。反过来，用基因靶向MCH神经元的钙指示剂进行神经网络成像显示，浴加OH肽引起的兴奋仅发生在少数MCH细胞中。总体而言，我们的数据提供了功能性微回路证据，表明LH内的前馈回路可能有助于睡眠和清醒信号之间进行适当切换，从而可能预防睡眠障碍。
