The Network Mechanism of the Central Circadian Pacemaker of the SCN: Do AVP Neurons Play a More Critical Role Than Expected?

The suprachiasmatic nucleus (SCN) functions as the central circadian pacemaker in mammals and entrains to the environmental light/dark cycle. It is composed of multiple types of GABAergic neurons, and interneuronal communications among these neurons are essential for the circadian pacemaking of the SCN. However, the mechanisms underlying the SCN neuronal network remain unknown. This review will provide a brief overview of the current knowledge concerning the differential roles of multiple neuropeptides and neuropeptide-expressing neurons in the SCN, especially focusing on the emerging roles of arginine vasopressin-producing neurons uncovered by recent studies utilizing neuron type-specific genetic manipulations in mice

The roles of orexins in sleep/wake regulation

Orexin A and orexin B are hypothalamic neuropeptides initially identified as endogenous ligands for two orphan G-protein coupled receptors (GPCRs). A deficiency of orexin signaling results in the sleep disorder narcolepsy-cataplexy in humans, dogs, and rodents, a sleep disorder characterized by excessive daytime sleepiness and cataplexy. Multiple approaches, including molecular genetic, electrophysiological, pharmacological, and neuroanatomical studies have suggested that orexins play critical roles in the maintenance of wakefulness by regulating the function of monoaminergic and cholinergic neurons that are implicated in the regulation of wakefulness. Here, I review recent advances in the understanding of how orexins regulate sleep/wakefulness and prevent narcolepsy. © 2017 Elsevier Ireland Ltd and Japan Neuroscience Society.Embargo Period 12 month

Integrative physiology of orexins and orexin receptors.

金沢大学医薬保健研究域医学系Recent studies have established that the orexin system is a critical regulator of sleep/wake states. Deficiency of orexin signaling results in the sleep disorder narcolepsy-cataplexy in humans, dogs, and rodents. These findings have brought about the possibility of novel therapies for sleep disorders including narcolepsy-cataplexy. Furthermore, accumulating evidence has indicated that the orexin system regulates sleep and wakefulness through interactions with neuronal systems that regulate emotion, reward, and energy homeostasis. This review presents and discusses the current understanding of the integrative physiology of the orexin system

Orexin (Hypocretin) receptor agonists and antagonists for treatment of sleep disorders: Rationale for development and current status

Orexin A and orexin B are hypothalamic neuropeptides initially identified as endogenous ligands for two orphan G-protein coupled receptors (GPCRs). They play critical roles in the maintenance of wakefulness by regulating function of monoaminergic and cholinergic neurons that are implicated in the regulation of wakefulness. Loss of orexin neurons in humans is associated with narcolepsy, a sleep disorder characterized by excessive daytime sleepiness and cataplexy, further suggesting the particular importance of orexin in the maintenance of the wakefulness state. These findings have encouraged pharmaceutical companies to develop drugs targeting orexin receptors as novel medications of sleep disorders, such as narcolepsy and insomnia. Indeed, phase III clinical trials were completed last year of suvorexant, a non-selective (dual) antagonist for orexin receptors, for the treatment of primary insomnia, and demonstrate promising results. The New Drug Application (NDA) for suvorexant has been submitted to the US FDA. Thus, the discovery of a critical role played by the orexin system in the regulation of sleep/wakefulness has opened the door of a new era for sleep medicine. © 2013 Springer International Publishing Switzerland

Connectomics of orexin-producing neurons: interface of systems of emotion, energy homeostasis and arousal

金沢大学医薬保健研究域医学系Avoiding danger and finding food, which are life-sustaining activities that are regulated by emotion, reward and energy balance, require proper wakefulness. The orexin system controls sleep and wakefulness through interactions with systems that regulate emotion, reward and energy homeostasis. Recent findings have brought about the possibility of novel therapies targeting the orexin system for sleep disorders, including insomnia and narcolepsy-cataplexy, as well as other pathological conditions such as obesity and drug addiction . In this review, we will discuss the current understanding of the integrative physiology and clinical perspectives of the orexin system. We will briefly review signaling through orexin A and B receptors and discuss the role of orexins in the pathophysiology of narcolepsy. We will also examine connections between orexin neurons and other brain areas involved in feeding behavior, reward and emotion. Finally, we will consider the therapeutic potential of drugs that target orexin receptors. © 2011 Elsevier Ltd. All rights reserved

Bmal1 in the nervous system is essential for normal adaptation of circadian locomotor activity and food intake to periodic feeding

Temporal restriction of feeding can entrain circadian behavioral and physiological rhythms in mammals. These changes in biological rhythms are postulated to be brought about by a putative food-entrainable oscillator (FEO) that is independent of the suprachiasmatic nucleus (SCN). However, the anatomical substrates and molecular machinery of FEO remain elusive. We report here that mice with a nervous system-specific deletion of Bmal1, an essential clock component, had a marked deficit in entrainment of locomotor activity by periodic feeding, accompanied by reduced food intake and subsequent loss of body weight. These mice exhibited a nearly normal light-entrainable activity rhythm driven by the SCN, because deletion of the Bmal1 gene in the SCN was only partial. These findings suggest that an SCN-independent FEO in the nervous system requires Bmal1 and plays a critical role in adaptation of circadian locomotor activity and food intake to periodic feeding. © 2011 the authors

Pharmacogenetic dissection of neural mechanisms underlying the regulation of sleep-wakefulness using DREADDs

Sleep and wakefulness are controlled by a complex network of neurons harboring diverse neurochemical characteristics, including glutamatergic, GABAergic, monoaminergic, cholinergic, and peptidergic neurons. To understand the precise role of each type of neuron in this circuit, it is useful to artificially manipulate the activity of a particular type of neuron to see its effect on behavior. The DREADD system has made such a strategy possible. Here, we review our recent work using DREADD to pharmacogenetically dissect neural mechanisms regulating sleep-wakefulness, describe the protocol we used, and discuss the technical aspects of our studies. © Springer Science+Business Media New York 2015. All rights reserved.Book Chapter, Embargo Period 12 month

Molecular Basis and Disorders of Control of Apetite and Fat Accumulation

金沢大学医薬保健研究域医学系本研究では、食欲･食物探索活動と食物摂取のタイミングを合わせ、限られた食餌機会を有効に利用するための第2の概日ペースメーカー「食餌同調性概日ペースメーカー」の神経基盤の解明を進めるとともに、食餌同調性概日ペースメーカーによる末梢臓器機能の調節様式を明らかにすることを目的した。食餌同調性概日ペースメーカー存在部位の絞り込みでは、SCNを除いた視床下部で特異的にBmal1（概日分子時計に必須の因子）を欠損したマウスを作製し、その食餌同調性概日行動リズムを検討した。しかし、用いたCreドライバーマウス自体で食餌同調性の食物探索行動が顕著に減弱してしまい、視床下部特異的Bmal1欠損の影響を調べることができなかった。また、以前我々は、視床下部背内側核緻密部を食餌同調性概日ペースメーカーの座と提唱したが、当該領域に特異的にCreを発現するトランスジェニックマウスを見出した。SCN以外の脳領域でBmal1を欠損したマウスでは給餌時刻に合わせた食物探索活動や摂食が著しく減少する。この「脳内食餌同調性概日ペースメーカーを特異的に欠損したモデルマウス」を用いて、諸臓器に内在する末梢概日時計を脳内食餌同調性概日ペースメーカーが調節する可能性について検討し、胃内在性概日時計の食餌への同調を促進することを明らかにした。しかしながらこのモデルマウスにおいて、グレリン血中濃度の食餌性同調性概日リズムについては異常が観察されなかった。脳内の食餌同調性概日ペースメーカーは餌探索活動や食欲などの脳機能を制御する一方で、末梢臓器機能の調節には大きな役割は果たさない可能性が考えられた。研究課題/領域番号:25126708, 研究期間(年度):2013-04-01 – 2015-03-3

"LIVING IN SPACE" - Integral Understanding of life-regulation mechanism from "SPACE"

金沢大学医薬保健研究域医学系概日リズム周期の操作は地球外生活に有用な技術となる。概日リズム中枢・視交叉上核(SCN)は、多種ニューロンから成るネットワークである。本研究では、SCN神経ネットワークの概日周期決定機構を理解し、さらに周期操作方法の開発を目指す。以前、AVPニューロンのみで細胞時計周期を長くする(casein kinase 1d: CK1dを欠損する)と、概日行動リズムの周期も延長することから、AVPニューロンが概日周期を決定するペースメーカー細胞の少なくとも一部であることを見出した。昨年度はCK1dをSCN全体、AVPニューロンのみ、VIPニューロンのみで欠損したマウスの行動周期を比較し、AVPニューロンがSCN全体が発振する概日周期の主要な決定要因と結論した。本年度は各マウス系統のSCNスライスの概日リズムを、Per2::Lucレポーターマウスを用いた発光イメージングで解析した。AVPニューロン特異的欠損マウスは行動リズム周期延長にもかかわらず、SCNスライスのPER2::LUCリズムに一貫した周期延長が再現されない。in vivoではSCN背側部（AVPニューロンが主）と腹側部が相互作用し単一の長周期をSCNが発振するが、スライスでは神経連絡や細胞外環境が保たれず、腹側部が優位になり背側部の周期までを制御すると考えられた。SCN全体欠損マウスではスライスでも比較的長期間周期延長が観察されたが、振動は明らかに減衰した。腹側部－背側部相互作用の分子実体を明らかにすべく、AVPニューロン特異的欠損マウスのSCNスライスで周期延長を再現できる薬理学的処理を検索中で、手がかりを得つつある。またファイバーフォトメトリーを用い、当該マウスの生体内でのSCN活動リズムを測定中である。概日リズム操作も行い、化学遺伝学でVIPニューロンを刺激すると、行動リズムが時刻依存的にシフトすることを見いだした。研究課題/領域番号:18H04972, 研究期間(年度):2018-04-01 – 2020-03-31出典：研究課題「概日リズム周期の決定機構解明と操作」課題番号18H04972（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PUBLICLY-18H04972/）を加工して作

Manipulating the Cellular Circadian Period of Arginine Vasopressin Neurons Alters the Behavioral Circadian Period

As the central pacemaker in mammals, the circadian clock in the suprachiasmatic nucleus (SCN) of the hypothalamus is a heterogeneous structure consisting of multiple types of GABAergic neurons with distinct chemical identities [1, 2]. Although individual cells have a cellular clock driven by autoregulatory transcriptional/translational feedback loops of clock genes, interneuronal communication among SCN clock neurons is likely essential for the SCN to generate a highly robust, coherent circadian rhythm [1]. However, neuronal mechanisms that determine circadian period length remain unclear. The SCN is composed of two subdivisions: a ventral core region containing vasoactive intestinal peptide (VIP)-producing neurons and a dorsal shell region characterized by arginine vasopressin (AVP)-producing neurons. Here we examined whether AVP neurons act as pacemaker cells that regulate the circadian period of behavior rhythm in mice. The deletion of casein kinase 1 delta (CK1δ) specific to AVP neurons, which was expected to lengthen the period of cellular clocks [3–6], lengthened the free-running period of circadian behavior as well. Conversely, the overexpression of CK1δ specific to SCN AVP neurons shortened the free-running period. PER2::LUC imaging in slices confirmed that cellular circadian periods of the SCN shell were lengthened in mice without CK1δ in AVP neurons. Thus, AVP neurons may be an essential component of circadian pacemaker cells in the SCN. Remarkably, the alteration of the shell-core phase relationship in the SCN of these mice did not impair the generation per se of circadian behavior rhythm, thereby underscoring the robustness of the SCN network. © 2016 Elsevier LtdEmbargo Period 12 month