Orexin neurons suppress narcolepsy via 2 distinct efferent pathways

Abstract

The loss of orexin neurons in humans is associated with the sleep disorder narcolepsy, which is characterized by excessive daytime sleepiness and cataplexy. Mice lacking orexin peptides, orexin neurons, or orexin receptors recapitulate human narcolepsy phenotypes, further highlighting a critical role for orexin signaling in the maintenance of wakefulness. Despite the known role of orexin neurons in narcolepsy, the precise neural mechanisms downstream of these neurons remain unknown. We found that targeted restoration of orexin receptor expression in the dorsal raphe (DR) and in the locus coeruleus (LC) of mice lacking orexin receptors inhibited cataplexy-like episodes and pathological fragmentation of wakefulness (i.e., sleepiness), respectively. The suppression of cataplexy-like episodes correlated with the number of serotonergic neurons restored with orexin receptor expression in the DR, while the consolidation of fragmented wakefulness correlated with the number of noradrenergic neurons restored in the LC. Furthermore, pharmacogenetic activation of these neurons using designer receptor exclusively activated by designer drug (DREADD) technology ameliorated narcolepsy in mice lacking orexin neurons. These results suggest that DR serotonergic and LC noradrenergic neurons play differential roles in orexin neuron-dependent regulation of sleep/wakefulness and highlight a pharmacogenetic approach for the amelioration of narcolepsy. IntroductionThe neuropeptides orexin A and orexin B (also termed hypocretin-1 and hypocretin-2, respectively) are implicated in feeding, the reward system, and sleep/wake regulation (1). They act on the G protein-coupled receptors orexin receptor type 1 (OX1R) and OX2R. Degenerative loss of orexin neurons in humans is associated with narcolepsy, a debilitating neurological disorder that provides a unique perspective on the mechanisms of sleep/wakefulness control (2). The syndrome consists of excessive daytime sleepiness that often results in sleep attacks (sudden onset of non-rapid eye movement [NREM] sleep), cataplexy (sudden bilateral skeletal muscle weakening triggered by emotions, without consciousness impairment), hypnagogic hallucinations, and sleep paralysis.The symptoms of narcolepsy can be divided into 2 independent pathological phenomena (1, 2). The first is dysregulation of NREM sleep onset: the inability to maintain a consolidated awake period, characterized by abrupt transitions from wakefulness to NREM sleep. This phenomenon manifests clinically as excessive daytime sleepiness or sleep attacks. The second is dysregulation of rapid eye movement (REM) sleep onset: the pathological intrusion of REM sleep or REM atonia into wakefulness or at sleep onset. It is during these periods that patients may experience cataplexy, hypnagogic hallucinations, and sleep paralysis.Similarly, mice with targeted deletion of the prepro-orexin gene (orexin -/-mice), mice in which orexin neurons are specifically ablated (orexin/ataxin-3 mice), and mice that lack both orexin receptors (Ox1r -/-Ox2r ...

Lateral Hypothalamus GABAergic Neurons Modulate Consummatory Behaviors Regardless of the Caloric Content or Biological Relevance of the Consumed Stimuli

“…This allowed us to rule out a role for the ZI and to conclude with confidence that GABAergic neurons, specifically in the LH, modulate consummatory behaviors. Finally, functional DREADD activity has been verified in numerous previous citations (Ferguson et al, 2013;Hasegawa et al, 2014;Krashes et al, 2011;Sasaki et al, 2011), and we showed that our Vgat-irescre mice expressing the AAV8-hSyn-DIO-hM3D(Gq)-mCherry DREADD in the LH exhibited increased c-Fos expression and electrophysiological activity following CNO application (see Supplementary Materials, Supplementary Figures S1 and S2). In summary, here we provide the first direct evidence that the LH GABAergic neurons under investigation modulate the consumption of any available stimulus, include those entailing calories (food, sucrose, and ethanol), those lacking calories (saccharin and water), and those lacking biological relevance (wood).…”

Nonpeptide orexin type-2 receptor agonist ameliorates narcolepsy-cataplexy symptoms in mouse models

“…In a previous report (17), the targeted restoration of OX2R expression in dorsal raphe, and of OX1R in the locus coeruleus, in mice lacking orexin receptors inhibited cataplexy-like episodes and pathological fragmentation of wakefulness, respectively, suggesting a role for OX1R in the consolidation of wakefulness. Considering these results, additional activation of OX1R may be necessary for full recovery of pathological fragmentation of wakefulness in narcoleptic mice.…”

“…Although these results suggest that orexin replacement could be an effective mechanistic therapy, orexins do not efficiently cross the blood-brain barrier (15) and are therefore difficult to use as a clinical drug. Because deficiency of OX2R signaling is primarily responsible for sleepiness and cataplexy-like episodes (6,(16)(17)(18), nonpeptidic OX2R agonists are promising candidates for a therapeutic agent to treat narcolepsy. We recently discovered a potent nonpeptidic OX2R agonist, YNT-185 (compound 30 in ref.…”

Pharmacogenetic Dissection of Neural Mechanisms Underlying the Regulation of Sleep–Wakefulness Using DREADDs

“…When AAV-Pet1/hM3Dq was microinjected into the DR, hM3Dq mRNA expression was detected in 78.4 ± 1.5% of serotonergic neurons in the DR, and 83.1 ± 1.0% of hM3Dq(+) cells were serotonergic (7). No hM3Dq mRNA expression was detected in the area surrounding the DR. I.p.…”

“…Since the development of DREADD technology by Dr. Bryan Roth's group at the University of North Carolina (1, 2), we have utilized DREADD technology to dissect neural circuits regulating the vigilance states. We so far have demonstrated (i) that changes in the activity of orexin neurons can alter the behavioral state of animals (6), (ii) that activation of dorsal raphe (DR) serotonergic neurons and locus coeruleous (LC) noradrenergic neurons suppress cataplexy and fragmentation of wakefulness, respectively, in narcoleptic mice (7), and (iii) that stimulation of GABAergic neurons in the preoptic area (POA) leads to an increase in the amount of non-rapid eye movement (NREM) sleep (8). These findings will be described below in more detail.…”