Orexin OX2 Receptor Antagonists as Sleep Aids

Effects of methamphetamine on actigraphy-based sleep parameters in female rhesus monkeys: Orexin receptor mechanisms

BACKGROUND

The orexin system has been implicated as a mechanism underlying insomnia and methamphetamine-induced sleep disruptions, with a potential role for OX2 receptors in the sleep-modulating effects of orexin. The aim of the present study was to investigate the extent to which orexin receptors mediate the effects of acute methamphetamine administration on actigraphy-based sleep in female rhesus monkeys.

METHODS

Actigraphy-based sleep measures were obtained in female rhesus monkeys (n=5) under baseline and acute test conditions. First, morning (10h) i.m. injections of methamphetamine (0.03 - 0.56mg/kg) were administered to determine the effects of methamphetamine alone. Then, saline or methamphetamine (0.3mg/kg) were administered at 10h, and evening (17h30) oral treatments with vehicle, the non-selective orexin receptor antagonist suvorexant (1 - 10mg/kg, p.o.), or the OX2-selective orexin receptor antagonist MK-1064 (1 - 10mg/kg, p.o.) were given. The ability of suvorexant and MK-1064 (10mg/kg, p.o.) to improve actigraphy-based sleep was also assessed in a group of female monkeys quantitatively identified with "short-duration sleep" (n=4).

RESULTS

Methamphetamine dose-dependently disrupted actigraphy-based sleep parameters. Treatment with either suvorexant or MK-1064 dose-dependently improved actigraphy-based sleep in monkeys treated with methamphetamine. Additionally, both suvorexant and MK-1064 promoted actigraphy-based sleep in a group of monkeys with baseline short actigraphy-based sleep.

CONCLUSIONS

These findings suggest that orexin-mediated mechanisms play a role in the effects of methamphetamine on actigraphy-based sleep in female monkeys. Targeting the orexin system, in particular OX2 receptors, could be an effective option for treating sleep disruptions observed in individuals with methamphetamine use disorder.

Orexin 2 receptor antagonism sex-dependently improves sleep/wakefulness and cognitive performance in tau transgenic mice

BACKGROUND AND PURPOSE

Tau pathology contributes to a bidirectional relationship between sleep disruption and neurodegenerative disease. Tau transgenic rTg4510 mice model tauopathy symptoms, including sleep/wake disturbances, which manifest as marked hyperarousal. This phenotype can be prevented by early transgene suppression; however, whether hyperarousal can be rescued after onset is unknown.

EXPERIMENTAL APPROACH

Three 8-week experiments were conducted with wild-type and rTg4510 mice after age of onset of hyperarousal (4.5 months): (1) Tau transgene suppression with doxycycline (200 ppm); (2) inactive phase rapid eye movement (REM) sleep enhancement with the dual orexin receptor antagonist suvorexant (50 mg·kg-1 ·day-1 ); or (3) Active phase non-NREM (NREM) and REM sleep enhancement using the selective orexin 2 (OX2 ) receptor antagonist MK-1064 (40 mg·kg-1 ·day-1 ). Sleep was assessed using polysomnography, cognition using the Barnes maze, and tau pathology using immunoblotting and/or immunohistochemistry.

KEY RESULTS

Tau transgene suppression improved tauopathy and hippocampal-dependent spatial memory, but did not modify hyperarousal. Pharmacological rescue of REM sleep deficits did not improve spatial memory or tau pathology. In contrast, normalising hyperarousal by increasing both NREM and REM sleep via OX2 receptor antagonism restored spatial memory, independently of tauopathy, but only in male rTg4510 mice. OX2 receptor antagonism induced only short-lived hypnotic responses in female rTg4510 mice and did not improve spatial memory, indicating a tau- and sex-dependent disruption of OX2 receptor signalling.

CONCLUSIONS AND IMPLICATIONS

Pharmacologically reducing hyperarousal corrects tau-induced sleep/wake and cognitive deficits. Tauopathy causes sex-dependent disruptions of OX2 receptor signalling/function, which may have implications for choice of hypnotic therapeutics in tauopathies.

Suvorexant, a Novel Dual Orexin Receptor Antagonist, for the Management of Insomnia

Purpose of Review

The present investigation is a comprehensive review regarding the use of Suvorexant for insomnia treatment. It covers the background, pathophysiology, and significance of addressing insomnia, the pharmaceutical details of Suvorexant, and its safety, efficacy, and implications in treating insomnia. We further discuss Suvorexant's role in targeting insomnia with other comorbidities.

Recent Findings

Insomnia refers to poor quality and/or quantity of sleep. While there are many existing treatments such as benzodiazepines, melatonin agonists, TCAs, and atypical antipsychotics used to target various receptors involved in normal induction and maintenance of sleep, Suvorexant is an antagonist that specifically targets orexin receptors. Recent clinical studies suggest that Suvorexant is both clinically safe and effective. Quantity and quality of sleep are measured in various ways, yet the consensus points towards Suvorexant's effectiveness in improving sleep time, onset, latency, and quality compared to placebo. In addition to helping improve isolated insomnia, Suvorexant helps improve sleep in patients that have other comorbidities such as obstructive sleep apnea, Alzheimer's disease, dementia, acute stroke, and delirium. While Suvorexant is safe, there are still adverse effects associated with the drug that needs to be considered. The most common adverse effects include dizziness, somnolence, headaches, and cognitive impairment.

Summary

Insomnia is a major public health concern that affects many people worldwide and has been linked to many adverse health outcomes. While there are existing treatments that target different receptors and pathways of normal sleep induction and maintenance, Suvorexant is a novel drug that targets dual orexin receptors. Its safety and efficacy, mechanism of action, pharmacokinetic parameters, and relative lack of rebound and withdrawal effects render suvorexant a reliable choice for the treatment of insomnia.

Cost-effectiveness analysis of lemborexant for treating insomnia in Japan: a model-based projection, incorporating the risk of falls, motor vehicle collisions, and workplace accidents

BACKGROUND

Lemborexant has demonstrated statistically significant improvements in sleep onset and sleep maintenance compared with placebo and zolpidem tartrate extended release, measured both objectively using polysomnography and subjectively using sleep diaries, in the phase 3 clinical trial SUNRISE 1. This study evaluated the cost-effectiveness of lemborexant compared with suvorexant, zolpidem immediate release (IR), and untreated insomnia.

METHODS

A decision-tree model was developed for falls, motor vehicle collisions, and workplace accidents associated with insomnia and insomnia treatments from a Japanese healthcare perspective and with a 6-month time horizon. The model extracted subjective sleep onset latency treatment responses and disutility values for non-responders from SUNRISE 1. Cost-effectiveness was assessed using incremental cost per quality-adjusted life year (QALY) gained. One-way and probabilistic sensitivity analyses were conducted to evaluate the impact of parameter uncertainty on the results.

RESULTS

In the base-case analysis, the mean estimated QALYs for lemborexant, suvorexant, zolpidem-IR, and untreated insomnia were 0.4220, 0.4204, 0.4113, and 0.4163, and expected medical costs were JPY 34 034, JPY 38 371, JPY 38 139, and JPY 15 383, respectively. Lemborexant saved JPY 4337 and JPY 4105 compared with suvorexant or zolpidem-IR, respectively, while conferring QALY benefits. The incremental cost-effectiveness ratio (ICER) of lemborexant compared with that of untreated insomnia was JPY 3 220 975 /QALY. Lemborexant was dominant over suvorexant and zolpidem-IR and was cost-effective when compared with untreated insomnia. Sensitivity analyses supported the results' robustness.

CONCLUSIONS

In a Japanese clinical practice setting, lemborexant may represent a better investment for treating insomnia in the healthcare system in Japan.

Effects of single and dual hypocretin-receptor blockade or knockdown of hypocretin projections to the central amygdala on alcohol drinking in dependent male rats

Hypocretin/Orexin (HCRT) is a neuropeptide that is associated with both stress and reward systems in humans and rodents. The different contributions of signaling at hypocretin-receptor 1 (HCRT-R1) and hypocretin-receptor 2 (HCRT-R2) to compulsive alcohol drinking are not yet fully understood. Thus, the current studies used pharmacological and viral-mediated targeting of HCRT to determine participation in compulsive alcohol drinking and measured HCRT-receptor mRNA expression in the extended amygdala of both alcohol-dependent and non-dependent male rats. Rats were made dependent through chronic intermittent exposure to alcohol vapor and were tested for the acute effect of HCRT-R1-selective (SB-408124; SB-R1), HCRT-R2-selective (NBI-80713; NB-R2), or dual HCRT-R1/2 (NBI-87571; NB-R1/2) antagonism on alcohol intake. NB-R2 and NB-R1/2 antagonists each dose-dependently decreased overall alcohol drinking in alcohol-dependent rats, whereas, SB-R1 decreased alcohol drinking in both alcohol-dependent and non-dependent rats at the highest dose (30 mg/kg). SB-R1, NB-R2, and NB-R1/2 treatment did not significantly affect water drinking in either alcohol-dependent or non-dependent rats. Additional PCR analyses revealed a significant decrease in Hcrtr1 mRNA expression within the central amygdala (CeA) of dependent rats under acute withdrawal conditions compared to nondependent rats. Lastly, a shRNA-encoding adeno-associated viral vector with retrograde function was used to knockdown HCRT in CeA-projecting neurons from the lateral hypothalamus (LH). LH-CeA HCRT knockdown significantly attenuated alcohol self-administration in alcohol-dependent rats. These observations suggest that HCRT signaling in the CeA is necessary for alcohol-seeking behavior during dependence. Together, these data highlight a role for both HCRT-R1 and -R2 in dependent alcohol-seeking behavior.

Hypocretins (orexins): The ultimate translational neuropeptides

The hypocretins (Hcrts), also known as orexins, are two neuropeptides produced exclusively in the lateral hypothalamus. They act on two specific receptors that are widely distributed across the brain and involved in a myriad of neurophysiological functions that include sleep, arousal, feeding, reward, fear, anxiety and cognition. Hcrt cell loss in humans leads to narcolepsy with cataplexy (narcolepsy type 1), a disorder characterized by intrusions of sleep into wakefulness, demonstrating that the Hcrt system is nonredundant and essential for sleep/wake stability. The causal link between Hcrts and arousal/wakefulness stabilisation has led to the development of a new class of drugs, Hcrt receptor antagonists to treat insomnia, based on the assumption that blocking orexin-induced arousal will facilitate sleep. This has been clinically validated: currently, two Hcrt receptor antagonists are approved to treat insomnia (suvorexant and lemborexant), with a New Drug Application recently submitted to the US Food and Drug Administration for a third drug (daridorexant). Other therapeutic applications under investigation include reduction of cravings in substance-use disorders and prevention of neurodegenerative disorders such as Alzheimer's disease, given the apparent bidirectional relationship between poor sleep and worsening of the disease. Circuit neuroscience findings suggest that the Hcrt system is a hub that integrates diverse inputs modulating arousal (e.g., circadian rhythms, metabolic status, positive and negative emotions) and conveys this information to multiple output regions. This neuronal architecture explains the wealth of physiological functions associated with Hcrts and highlights the potential of the Hcrt system as a therapeutic target for a number of disorders. We discuss present and future possible applications of drugs targeting the Hcrt system for the treatment of circuit-related neuropsychiatric and neurodegenerative conditions.

Orexin Signaling: A Complex, Multifaceted Process

The orexin system comprises two G protein-coupled receptors, OX₁ and OX₂ receptors (OX₁R and OX₂R, respectively), along with two endogenous agonists cleaved from a common precursor (prepro-orexin), orexin-A (OX-A) and orexin-B (OX-B). For the receptors, a complex array of signaling behaviors has been reported. In particular, it becomes obvious that orexin receptor coupling is very diverse and can be tissue-, cell- and context-dependent. Here, the early signal transduction interactions of the orexin receptors will be discussed in depth, with particular emphasis on the direct G protein interactions of each receptor. In doing so, it is evident that ligands, additional receptor-protein interactions and cellular environment all play important roles in the G protein coupling profiles of the orexin receptors. This has potential implications for our understanding of the orexin system’s function in vivo in both central and peripheral environments, as well as the development of novel agonists, antagonists and possibly allosteric modulators targeting the orexin system.

Differential sleep/wake response and sex effects following acute suvorexant, MK-1064 and zolpidem administration in the rTg4510 mouse model of tauopathy

Background and Purpose

Transgenic mouse models of tauopathy display prominent sleep/wake disturbances which manifest primarily as a hyperarousal phenotype during the active phase, suggesting that tau pathology contributes to sleep/wake changes. However, no study has yet investigated the effect of sleep‐promoting compounds in these models. Such information has implications for the use of hypnotics as potential therapeutic tools in tauopathy‐related disorders.

Experimental Approach

This study examined polysomnographic recordings in 6‐6.5‐month‐old male and female rTg4510 mice following acute administration of suvorexant (50 mg·kg⁻¹), MK‐1064 (30 mg·kg⁻¹) or zolpidem (10 mg·kg⁻¹), administered at the commencement of the active phase.

Key Results

Suvorexant, a dual OX receptor antagonist, promoted REM sleep in rTg4510 mice, without affecting wake or NREM sleep. MK‐1064, a selective OX₂ receptor antagonist, reduced wake and increased NREM and total sleep time. MK‐1064 normalised the hyperarousal phenotype of male rTg4510 mice, whereas female rTg4510 mice exhibited a more transient response. Zolpidem, a GABA_A receptor positive allosteric modulator, decreased wake and increased NREM sleep in both male and female rTg4510 mice. Of the three compounds, the OX₂ receptor antagonist MK‐1064 promoted and normalised physiologically normal sleep, especially in male rTg4510 mice.

Conclusions and Implications

Our findings indicate that hyperphosphorylated tau accumulation and associated hyperarousal does not significantly alter the responses of tauopathy mouse models to hypnotics. However, the sex differences observed in the sleep/wake response of rTg4510 mice to MK‐1064, but not suvorexant or zolpidem, raise questions about therapeutic implications for the use of OX₂ receptor antagonists in human neurodegenerative disorders.

The dual orexin receptor antagonist almorexant blocks the sleep-disrupting and daytime stimulant effects of methamphetamine in rhesus monkeys

BACKGROUND

The present study investigated the effects of the dual orexin receptor antagonist (DORA) almorexant, a sleep-modulating drug, on the sleep-disrupting effects of methamphetamine in adult rhesus monkeys.

METHODS

Monkeys were fitted with primate collars to which actigraphy monitors were attached. To determine the effects of methamphetamine on daytime activity and sleep-like parameters, monkeys were given acute injections of vehicle or methamphetamine (0.03, 0.1 or 0.3 mg/kg, i.m.) in the morning (9:00 h) (n = 4 males). We then determined the ability of almorexant to alter the daytime and/or sleep-like effects of the largest (effective) dose of methamphetamine. Vehicle or almorexant (1, 3 or 10 mg/kg, i.m.) were administered in the evening (16:30 h, 1.5 h before "lights off") following morning (9:00 h) administration of methamphetamine (0.3 mg/kg, i.m.), or as a pretreatment (8:30 h) before methamphetamine injections (9:00 h) (n = 4 males). The ability of almorexant (10 mg/kg) to improve sleep-like behaviors also was assessed in a group of monkeys quantitatively identified with short-duration sleep (n = 2 males, 2 females).

RESULTS

Morning methamphetamine administration dose-dependently impaired sleep in rhesus monkeys (0.3 mg/kg significantly increased sleep latency and decreased sleep efficiency). Administration of almorexant, both as a pretreatment or as an evening treatment, improved methamphetamine-induced sleep impairment in a dose dependent manner. Morning pretreatment with almorexant also blocked the daytime stimulant effects of methamphetamine. Evening, but not morning, treatment with almorexant in a group of monkeys with baseline short-duration sleep improved sleep measures.

CONCLUSIONS

Our findings indicate that orexin receptor systems are involved in methamphetamine-induced hyperarousal and sleep disruption.

Orexin receptors: Targets and applications

Over the years, elucidating targets from the neural circuits that can be used to treat disorders pertaining to the nervous system and extending their scope to other systems have always proved interesting to researchers. The role of various peptides and neurotransmitters has been elucidated and is being developed as therapeutic targets. Out of these, orexins are neuropeptides produced in the hypothalamus that stimulate a specific type of G-Protein coupled receptors (GPCR) called orexin receptors and bring about various physiological and pathological roles. Orexin receptors are of interest not only because of their wide applications such as insomnia, obesity, and inflammatory disorders but also because of their contribution to promising aspects of drug discovery such as optogenetics and their tremendous growth from the stage of being orphans to orexins. This review will discuss in detail the structure of orexin receptors, their physiological role, and various applications in disease states adding a note on agonists and antagonists and finally summarizing the recent drug approvals in the field.

Hypocretin/Orexin Receptor Pharmacology and Sleep Phases

The hypocretins/orexins are two excitatory neuropeptides, alternately called HCRT1 or orexin-A and HCRT2 or orexin-B, that are the endogenous ligands for two G-protein-coupled receptors, HCRTR1/OX1R and HCRTR2/OX2R. Shortly after the discovery of this system, degeneration of hypocretin/orexin-producing neurons was implicated in the etiology of the sleep disorder narcolepsy. The involvement of this system in a disorder characterized by the loss of control over arousal state boundaries also suggested its role as a critical component of endogenous sleep-wake regulatory circuitry. The broad projections of the hypocretin/orexin-producing neurons, along with differential expression of the two receptors in the projection fields of these neurons, suggest distinct roles for these receptors. While HCRTR1/OX1R is associated with regulation of motivation, reward, and autonomic functions, HCRTR2/OX2R is strongly linked to sleep-wake control. The association of hypocretin/orexin with these physiological processes has led to intense interest in the therapeutic potential of compounds targeting these receptors. Agonists and antagonists for the hypocretin/orexin receptors have shown potential for the treatment of disorders of excessive daytime somnolence and nocturnal hyperarousal, respectively, with the first antagonists approved by the US Food and Drug Administration (FDA) in 2014 and 2019 for the treatment of insomnia. These and related compounds have also been useful tools to advance hypocretin/orexin neurobiology.

The Dual Orexin Receptor Antagonist DORA-22 Improves Mild Stress-induced Sleep Disruption During the Natural Sleep Phase of Nocturnal Rats

Dual orexinergic antagonists (DORAs) have been recently developed as a pharmacotherapy alternative to established hypnotics. Hypnotics are largely evaluated in preclinical rodent models in the dark/active period yet should be ideally evaluated in the light/inactive period, analogous to when sleep disruption occurs in humans. We describe here the hypnotic efficacy of DORA-22 in rodent models of sleep disturbance produced by cage changes in the light/inactive period. Rats were administered DORA-22 or the GABA receptor-targeting hypnotic eszopiclone early in the light period, then exposed to six hourly clean cage changes with measurements of NREM sleep onset latency. Both compounds initially promoted sleep (hours 1 and 2), with DORA-22 exhibiting a more rapid hypnotic onset; and exhibited extended efficacy, evident six hours after administration in a sleep latencies test. A common complaint concerning hypnotic use is lingering hypersomnolence, and this is a concern in pharmacotherapy of the elderly. A second study was designed to determine a minimal dose of DORA-22 which would initially promote sleep but exhibit minimal extended hypnotic effect.Animals were administered DORA-22, then exposed for six hours to a single cage previously dirtied by a conspecific, followed by return to home cage. EEG measures indicated that all DORA-22 doses largely promoted sleep in the first hour. The lowest dose (1 mg/kg) did not decrease sleep onset latency at the six-hour timepoint, suggesting no residual hypersomnolence. We described here DORA-22 hypnotic efficacy during the normal sleep period of nocturnal rats, and demonstrate that well-chosen (low) hypnotic doses of DORA-22 may be hypnotically effective yet have minimal lingering effects.

Decreased Orexin Receptor 1 mRNA Expression in the Locus Coeruleus in Both Tau Transgenic rTg4510 and Tau Knockout Mice and Accompanying Ascending Arousal System Tau Invasion in rTg4510

BACKGROUND

Sleep/wake disturbances (e.g., insomnia and sleep fragmentation) are common in neurodegenerative disorders, especially Alzheimer's disease (AD) and frontotemporal dementia (FTD). These symptoms are somewhat reminiscent of narcolepsy with cataplexy, caused by the loss of orexin-producing neurons. A bidirectional relationship between sleep disturbance and disease pathology suggests a detrimental cycle that accelerates disease progression and cognitive decline. The accumulation of brain tau fibrils is a core pathology of AD and FTD-tau and clinical evidence supports that tau may impair the orexin system in AD/FTD. This hypothesis was investigated using tau mutant mice.

OBJECTIVE

To characterize orexin receptor mRNA expression in sleep/wake regulatory brain centers and quantify noradrenergic locus coeruleus (LC) and orexinergic lateral hypothalamus (LH) neurons, in tau transgenic rTg4510 and tau-/- mice.

METHODS

We used i n situ hybridization and immunohistochemistry (IHC) in rTg4510 and tau-/- mice.

RESULTS

rTg4510 and tau-/- mice exhibited a similar decrease in orexin receptor 1 (OX1R) mRNA expression in the LC compared with wildtype controls. IHC data indicated this was not due to decreased numbers of LC tyrosine hydroxylase-positive (TH) or orexin neurons and demonstrated that tau invades TH LC and orexinergic LH neurons in rTg4510 mice. In contrast, orexin receptor 2 (OX2R) mRNA levels were unaffected in either model.

CONCLUSION

The LC is strongly implicated in the regulation of sleep/wakefulness and expresses high levels of OX1R. These findings raise interesting questions regarding the effects of altered tau on the orexin system, specifically LC OX1Rs, and emphasize a potential mechanism which may help explain sleep/wake disturbances in AD and FTD.

Targeting the Orexin System for Prescription Opioid Use Disorder

Prescription opioids are potent analgesics that are used for clinical pain management. However, the nonmedical use of these medications has emerged as a major concern because of dramatic increases in abuse and overdose. Therefore, effective strategies to prevent prescription opioid use disorder are urgently needed. The orexin system has been implicated in the regulation of motivation, arousal, and stress, making this system a promising target for the treatment of substance use disorder. This review discusses recent preclinical studies that suggest that orexin receptor blockade could be beneficial for the treatment of prescription opioid use disorder.

Hypnotics with novel modes of action

Insomnia and, more generally, lack of sleep are on the rise. Traditionally treated by classical hypnotics, such as benzodiazepines and Z drugs, which both act on the GABA_A receptor, and other modalities, including nondrug therapies, such as cognitive behavioural therapy, there is a range of new hypnotics which are being developed or have recently received market approval. Suvorexant and the like target the orexin/hypocretin system: they should have less side effects in terms of drug-drug interactions with e.g. alcohol, less memory impairment and dependence potential compared to classical hypnotics.

The role of co-neurotransmitters in sleep and wake regulation

Sleep and wakefulness control in the mammalian brain requires the coordination of various discrete interconnected neurons. According to the most conventional sleep model, wake-promoting neurons (WPNs) and sleep-promoting neurons (SPNs) compete for network dominance, creating a systematic "switch" that results in either the sleep or awake state. WPNs and SPNs are ubiquitous in the brainstem and diencephalon, areas that together contain <1% of the neurons in the human brain. Interestingly, many of these WPNs and SPNs co-express and co-release various types of the neurotransmitters that often have opposing modulatory effects on the network. Co-transmission is often beneficial to structures with limited numbers of neurons because it provides increasing computational capability and flexibility. Moreover, co-transmission allows subcortical structures to bi-directionally control postsynaptic neurons, thus helping to orchestrate several complex physiological functions such as sleep. Here, we present an in-depth review of co-transmission in hypothalamic WPNs and SPNs and discuss its functional significance in the sleep-wake network.

Sleep Physiology, Circadian Rhythms, Waking Performance and the Development of Sleep-Wake Therapeutics

Disturbances of the sleep-wake cycle are highly prevalent and diverse. The aetiology of some sleep disorders, such as circadian rhythm sleep-wake disorders, is understood at the conceptual level of the circadian and homeostatic regulation of sleep and in part at a mechanistic level. Other disorders such as insomnia are more difficult to relate to sleep regulatory mechanisms or sleep physiology. To further our understanding of sleep-wake disorders and the potential of novel therapeutics, we discuss recent findings on the neurobiology of sleep regulation and circadian rhythmicity and its relation with the subjective experience of sleep and the quality of wakefulness. Sleep continuity and to some extent REM sleep emerge as determinants of subjective sleep quality and waking performance. The effects of insufficient sleep primarily concern subjective and objective sleepiness as well as vigilant attention, whereas performance on higher cognitive functions appears to be better preserved albeit at the cost of increased effort. We discuss age-related, sex and other trait-like differences in sleep physiology and sleep need and compare the effects of existing pharmacological and non-pharmacological sleep- and wake-promoting treatments. Successful non-pharmacological approaches such as sleep restriction for insomnia and light and melatonin treatment for circadian rhythm sleep disorders target processes such as sleep homeostasis or circadian rhythmicity. Most pharmacological treatments of sleep disorders target specific signalling pathways with no well-established role in either sleep homeostasis or circadian rhythmicity. Pharmacological sleep therapeutics induce changes in sleep structure and the sleep EEG which are specific to the mechanism of action of the drug. Sleep- and wake-promoting therapeutics often induce residual effects on waking performance and sleep, respectively. The need for novel therapeutic approaches continues not at least because of the societal demand to sleep and be awake out of synchrony with the natural light-dark cycle, the high prevalence of sleep-wake disturbances in mental health disorders and in neurodegeneration. Novel approaches, which will provide a more comprehensive description of sleep and allow for large-scale sleep and circadian physiology studies in the home environment, hold promise for continued improvement of therapeutics for disturbances of sleep, circadian rhythms and waking performance.

The hypocretin/orexin system as a target for excessive motivation in alcohol use disorders

The hypocretin/orexin (ORX) system has been repeatedly demonstrated to regulate motivation for drugs of abuse, including alcohol. In particular, ORX seems to be critically involved in highly motivated behaviors, as is observed in high-seeking individuals in a population, in the seeking of highly palatable substances, and in models of dependence. It seems logical that this system could be considered as a potential target for treatment for addiction, particularly alcohol addiction, as ORX pharmacological manipulations significantly reduce drinking. However, the ORX system also plays a role in a wide range of other behaviors, emotions, and physiological functions and is disrupted in a number of non-dependence-associated disorders. It is therefore important to consider how the ORX system might be optimally targeted for potential treatment for alcohol use disorders either in combination with or separate from its role in other functions or diseases. This review will focus on the role of ORX in alcohol-associated behaviors and whether and how this system could be targeted to treat alcohol use disorders while avoiding impacts on other ORX-relevant functions. A brief overview of the ORX system will be followed by a discussion of some of the factors that makes it particularly intriguing as a target for alcohol addiction treatment, a consideration of some potential challenges associated with targeting this system and, finally, some future directions to optimize new treatments.