Effect of repeated gaboxadol administration on night sleep and next-day performance in healthy elderly subjects

An examination of sleep spindle metrics in the Sleep Heart Health Study: superiority of automated spindle detection over total sigma power in assessing age-related spindle decline

BACKGROUND

Sleep spindle activity is commonly estimated by measuring sigma power during stage 2 non-rapid eye movement (NREM2) sleep. However, spindles account for little of the total NREM2 interval and therefore sigma power over the entire interval may be misleading. This study compares derived spindle measures from direct automated spindle detection with those from gross power spectral analyses for the purposes of clinical trial design.

METHODS

We estimated spindle activity in a set of 8,440 overnight electroencephalogram (EEG) recordings from 5,793 patients from the Sleep Heart Health Study using both sigma power and direct automated spindle detection. Performance of the two methods was evaluated by determining the sample size required to detect decline in age-related spindle coherence with each method in a simulated clinical trial.

RESULTS

In a simulated clinical trial, sigma power required a sample size of 115 to achieve 95% power to identify age-related changes in sigma coherence, while automated spindle detection required a sample size of only 60.

CONCLUSIONS

Measurements of spindle activity utilizing automated spindle detection outperformed conventional sigma power analysis by a wide margin, suggesting that many studies would benefit from incorporation of automated spindle detection. These results further suggest that some previous studies which have failed to detect changes in sigma power or coherence may have failed simply because they were underpowered.

Emerging therapeutic targets for narcolepsy

INTRODUCTION

Narcolepsy type 1 (NT1) and type 2 (NT2) are chronic sleep disorders primarily characterized by excessive daytime sleepiness (EDS), disturbed sleep-wake regulation, and reduced quality of life. The precise disease mechanism is unclear, but it is certain that in NT1 the hypocretin/orexin (Hcrt) system is affected. Current treatment options are symptomatic - they improve EDS and/or reduce cataplexy. Complete symptom control is relatively rare - particularly problematic is residual daytime sleepiness.

AREAS COVERED

This review discusses various emerging treatment targets for narcolepsy. The focus is on the Hcrt receptors but included are also wake-promoting pathways, and sleep-stabilization through GABAergic mechanisms. Additionally, we discuss the potential of targeting the likely autoimmune basis of narcolepsy. PubMed and ClinicalTrials.gov was searched through June 2021 for relevant information.

EXPERT OPINION

Targeting Hcrt receptors has the potential to alleviate narcolepsy symptoms. Results from ongoing drug development programs are promising, but care needs to be taken when evaluating potential side effects. It is still largely unknown what roles Hcrt receptors play in the periphery and how these might be affected by treatment. Immunotherapies could potentially target the core pathophysiology of narcolepsy, but more work is needed to identify the best therapeutic target for this approach.

Drug Screening and Drug Repositioning as Promising Therapeutic Approaches for Spinal Muscular Atrophy Treatment

Spinal muscular atrophy (SMA) is the most common genetic disease affecting infants and young adults. Due to mutation/deletion of the survival motor neuron (SMN) gene, SMA is characterized by the SMN protein lack, resulting in motor neuron impairment, skeletal muscle atrophy and premature death. Even if the genetic causes of SMA are well known, many aspects of its pathogenesis remain unclear and only three drugs have been recently approved by the Food and Drug Administration (Nusinersen-Spinraza; Onasemnogene abeparvovec or AVXS-101-Zolgensma; Risdiplam-Evrysdi): although assuring remarkable results, the therapies show some important limits including high costs, still unknown long-term effects, side effects and disregarding of SMN-independent targets. Therefore, the research of new therapeutic strategies is still a hot topic in the SMA field and many efforts are spent in drug discovery. In this review, we describe two promising strategies to select effective molecules: drug screening (DS) and drug repositioning (DR). By using compounds libraries of chemical/natural compounds and/or Food and Drug Administration-approved substances, DS aims at identifying new potentially effective compounds, whereas DR at testing drugs originally designed for the treatment of other pathologies. The drastic reduction in risks, costs and time expenditure assured by these strategies make them particularly interesting, especially for those diseases for which the canonical drug discovery process would be long and expensive. Interestingly, among the identified molecules by DS/DR in the context of SMA, besides the modulators of SMN2 transcription, we highlighted a convergence of some targeted molecular cascades contributing to SMA pathology, including cell death related-pathways, mitochondria and cytoskeleton dynamics, neurotransmitter and hormone modulation.

Conditioned Aversion and Neuroplasticity Induced by a Superagonist of Extrasynaptic GABAA Receptors: Correlation With Activation of the Oval BNST Neurons and CRF Mechanisms

THIP (gaboxadol), a superagonist of the δ subunit-containing extrasynaptic GABA_A receptors, produces persistent neuroplasticity in dopamine (DA) neurons of the ventral tegmental area (VTA), similarly to rewarding drugs of abuse. However, unlike them THIP lacks abuse potential and induces conditioned place aversion in mice. The mechanism underlying the aversive effects of THIP remains elusive. Here, we show that mild aversive effects of THIP were detected 2 h after administration likely reflecting an anxiety-like state with increased corticosterone release and with central recruitment of corticotropin-releasing factor corticotropin-releasing factor receptor 1 (CRF₁) receptors. A detailed immunohistochemical c-Fos expression mapping for THIP-activated brain areas revealed a correlation between the activation of CRF-expressing neurons in the oval nucleus of the bed nuclei of stria terminalis and THIP-induced aversive effects. In addition, the neuroplasticity of mesolimbic DA system (24 h after administration) and conditioned place aversion by THIP after four daily acute sessions were dependent on extrasynaptic GABA_A receptors (abolished in δ-GABA_A receptor knockout mice) and activation of the CRF₁ receptors (abolished in wildtype mice by a CRF₁ receptor antagonist). A selective THIP-induced activation of CRF-expressing neurons in the oval part of the bed nucleus of stria terminalis may constitute a novel mechanism for inducing plasticity in a population of VTA DA neurons and aversive behavioral states.

Sleep, cognition, and normal aging: integrating a half century of multidisciplinary research

Sleep is implicated in cognitive functioning in young adults. With increasing age, there are substantial changes to sleep quantity and quality, including changes to slow-wave sleep, spindle density, and sleep continuity/fragmentation. A provocative question for the field of cognitive aging is whether such changes in sleep physiology affect cognition (e.g., memory consolidation). We review nearly a half century of research across seven diverse correlational and experimental domains that historically have had little crosstalk. Broadly speaking, sleep and cognitive functions are often related in advancing age, though the prevalence of null effects in healthy older adults (including correlations in the unexpected, negative direction) indicates that age may be an effect modifier of these associations. We interpret the literature as suggesting that maintaining good sleep quality, at least in young adulthood and middle age, promotes better cognitive functioning and serves to protect against age-related cognitive declines.

Non-Benzodiazepine Receptor Agonists for Insomnia

Because of proven efficacy, reduced side effects, and less concern about addiction, non-benzodiazepine receptor agonists (non-BzRA) have become the most commonly prescribed hypnotic agents to treat onset and maintenance insomnia. First-line treatment is cognitive-behavioral therapy. When pharmacologic treatment is indicated, non-BzRA are first-line agents for the short-term and long-term management of transient and chronic insomnia related to adjustment, psychophysiologic, primary, and secondary causation. In this article, the benefits and risks of non-BzRA are reviewed, and the selection of a hypnotic agent is defined, based on efficacy, pharmacologic profile, and adverse events.

Acutely increasing δGABA(A) receptor activity impairs memory and inhibits synaptic plasticity in the hippocampus

Extrasynaptic γ-aminobutyric acid type A (GABA_A) receptors that contain the δ subunit (δGABA_A receptors) are expressed in several brain regions including the dentate gyrus (DG) and CA1 subfields of the hippocampus. Drugs that increase δGABA_A receptor activity have been proposed as treatments for a variety of disorders including insomnia, epilepsy and chronic pain. Also, long-term pretreatment with the δGABA_A receptor–preferring agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) enhances discrimination memory and increases neurogenesis in the DG. Despite the potential therapeutic benefits of such treatments, the effects of acutely increasing δGABA_A receptor activity on memory behaviors remain unknown. Here, we studied the effects of THIP (4 mg/kg, i.p.) on memory performance in wild-type (WT) and δGABA_A receptor null mutant (Gabrd^−/−) mice. Additionally, the effects of THIP on long-term potentiation (LTP), a molecular correlate of memory, were studied within the DG and CA1 subfields of the hippocampus using electrophysiological recordings of field potentials in hippocampal slices. The results showed that THIP impaired performance in the Morris water maze, contextual fear conditioning and object recognition tasks in WT mice but not Gabrd^−/− mice. Furthermore, THIP inhibited LTP in hippocampal slices from WT but not Gabrd^−/− mice, an effect that was blocked by GABA_A receptor antagonist bicuculline. Thus, acutely increasing δGABA_A receptor activity impairs memory behaviors and inhibits synaptic plasticity. These results have important implications for the development of therapies aimed at increasing δGABA_A receptor activity.

The Effects of Agonists of Ionotropic GABAAand Metabotropic GABABReceptors on Learning

The research described here investigates the role played by inhibitory processes in the discriminations made by the nervous system of humans and animals between familiar and unfamiliar and significant and nonsignificant events. This research compared the effects of two inhibitory mediators of gamma-aminobutyric acid (GABA): 1) phenibut, a nonselective agonist of ionotropic GABAAand metabotropic GABABreceptors and 2) gaboxadol a selective agonist of ionotropic GABAAreceptors on the process of developing active defensive and inhibitory conditioned reflexes in alert non-immobilized rabbits. It was found that phenibut, but not gaboxadol, accelerates the development of defensive reflexes at an early stage of conditioning. Both phenibut and gaboxadol facilitate the development of conditioned inhibition, but the effect of gaboxadol occurs at later stages of conditioning and is less stable than that of phenibut. The earlier and more stable effects of phenibut, as compared to gaboxadol, on storage in memory of the inhibitory significance of a stimulus may occur because GABABreceptors play the dominant role in the development of internal inhibition during an early stage of conditioning. On the other hand this may occur because the participation of both GABAAand GABABreceptors are essential to the process. We discuss the polyfunctionality of GABA receptors as a function of their structure and the positions of the relevant neurons in the brain as this factor can affect regulation of various types of psychological processes.

Memory consolidation — Mechanisms and opportunities for enhancement

Memory consolidation is the process by which relevant information is selected and transferred from a short-term, fragile state, into a stable, longer term domain from which it can be recalled. Effective memory underpins our ability to carry out everyday activities. When memory consolidation fails, such as in Alzheimer’s disease, the consequences can be devastating. Understanding the neurobiology of memory will help develop treatments for patients with memory loss. Here we describe the myriad processes involved in memory consolidation, including cholinergic and dopaminergic neurotransmission predominantly in hippocampal networks. We discuss established therapies as well as potential novel strategies for boosting cognition. Future approaches to enhancement of memory consolidation include not only pharmacological and neurosurgical treatments, but also lifestyle interventions — for example, modifications to sleep, exercise and diet.

EEG spectral power density profiles during NREM sleep for gaboxadol and zolpidem in patients with primary insomnia

There is significant interest in the functional significance and the therapeutic value of slow-wave sleep (SWS)-enhancing drugs. A prerequisite for studies of the functional differences is characterization of the electroencephalography (EEG) spectra following treatment in relevant patients. We evaluate for the first time gaboxadol and zolpidem treatments in insomniac patients using power spectra analysis. We carried out two randomized, double-blind, crossover studies. Study 1, 38 patients received gaboxadol 10 mg and 20 mg and zolpidem 10 mg; study 2, 23 patients received gaboxadol 5 mg and 15 mg. Treatments were administered during two nights and compared with placebo. Gaboxadol 10, 15 and 20 mg enhanced slow-wave activity (SWA) and theta power. In 1 Hz bins gaboxadol 10 and 20 mg enhanced power up to 9 Hz. In study 2, 15 mg gaboxadol showed a similar effect pattern. Zolpidem suppressed theta and alpha power, and increased sigma power, with no effect on SWA. In the 1 Hz bins zolpidem suppressed power between 5-10 Hz. Gaboxadol dose-dependently increased SWA and theta power in insomniac patients. In contrast, zolpidem did not affect SWA, reduced theta and alpha activity and enhanced sigma power. EEG spectral power differences may be consequences of the different mechanisms of action for zolpidem and the SWS-enhancing agent, gaboxadol.

EEG power spectra response to a 4-h phase advance and gaboxadol treatment in 822 men and women

STUDY OBJECTIVE

To explore the effect of gaboxadol on NREM EEG in transient insomnia using power spectral analysis and evaluate the response between men and women.

METHODS

This was a randomized, double-blind, 3-way, parallel-group transient insomnia study in 22 sleep laboratories. After a baseline night (N1), subjects underwent a 4-h phase-advance of their habitual sleep time the following night (N2). Healthy subjects aged 18-64 y were given single-blind placebo on N1 followed by double-blind treatment on N2 (gaboxadol 10 mg [n = 271], 15 mg [n = 274], or placebo [n = 277])

RESULTS

At baseline, women showed significantly greater values in low frequency activity (< 10 Hz) and in high spindle/low beta frequency activity (14-18 Hz) compared to men. During the phase advance (placebo N2-baseline N1), there was a significant increase in power within the high spindle/low beta frequency range (15-17 Hz) and a significant reduction in beta activity (20-32 Hz), which was greater in women than men. Gaboxadol induced a significant (dose-related) increase in low frequencies (< 8 Hz) and a significant (dose-related) decrease within the alpha/spindle range (11-12 Hz). The effect was dependent upon sex, with a greater magnitude of effect observed in women than men.

CONCLUSION

Gaboxadol shows a characteristic NREM EEG spectral profile in a model of transient insomnia. Men and women show clear differences in NREM EEG activity at baseline, to gaboxadol treatment and to phase-shifts in habitual sleep/wake times. The exact mechanisms underlying the sex differences remain unclear, but sex is an important variable in studies evaluating sleep and gaboxadol. TRIAL REGISTRY INFORMATION:

TRIAL REGISTRY

www.clinicaltrials.gov, study identifier: NCT00102167.

New guidelines for diagnosis and treatment of insomnia

The Brazilian Sleep Association brought together specialists in sleep medicine, in order to develop new guidelines on the diagnosis and treatment of insomnias. The following subjects were discussed: concepts, clinical and psychosocial evaluations, recommendations for polysomnography, pharmacological treatment, behavioral and cognitive therapy, comorbidities and insomnia in children. Four levels of evidence were envisaged: standard, recommended, optional and not recommended. For diagnosing of insomnia, psychosocial and polysomnographic investigation were recommended. For non-pharmacological treatment, cognitive behavioral treatment was considered to be standard, while for pharmacological treatment, zolpidem was indicated as the standard drug because of its hypnotic profile, while zopiclone, trazodone and doxepin were recommended.

Pimavanserin tartrate, a 5-HT(2A) receptor inverse agonist, increases slow wave sleep as measured by polysomnography in healthy adult volunteers

OBJECTIVE

Determine the effects of pimavanserin tartrate [ACP-103; N-(4-flurophenylmethyl)-N-(1-methylpiperidin-4-yl)-N'-(4-(2-methylpropyloxy)phenylmethyl)carbamide], a selective serotonin 5-HT(2A) receptor inverse agonist, on slow wave sleep (SWS), other sleep parameters, and attention/vigilance.

METHODS

Forty-five healthy adults were randomized to pimavanserin (1, 2.5, 5, or 20 mg) or placebo in a double-blind fashion (n=9/group). Pimavanserin or placebo was administered once daily in the morning for 13 consecutive days. The effects of pimavanserin were measured after the first dose and again after 13 days. Sleep parameters were measured by polysomnography. Effects on attention/vigilance were measured by a continuous performance task.

RESULTS

Compared to placebo, pimavanserin significantly increased SWS following single and multiple dose administration. Pimavanserin also decreased number of awakenings. PSG variables not affected by pimavanserin included sleep period time, total sleep time, sleep onset latency, number of stage shifts, total time awake, early morning wake, and microarousal index. Changes in sleep architecture parameters, sleep profile parameters, and spectral power density parameters were consistent with a selective increase in SWS. Pimavanserin did not adversely affect performance on the continuous performance test measured in the evening before or morning after polysomnography.

CONCLUSIONS

These data suggest that pimavanserin selectively increases slow wave sleep and decreases awakenings, an effect that does not diminish with repeated administration.

Alterations in cyclic alternating pattern associated with phase advanced sleep are differentially modulated by gaboxadol and zolpidem

OBJECTIVE

to evaluate cyclic alternating pattern (CAP) in a phase advance model of transient insomnia and the effects of gaboxadol and zolpidem.

DESIGN

a randomized, double-blind, cross-over study in which habitual sleep time was advanced by 4 h.

SETTING

6 sleep research laboratories in US PARTICIPANTS: 55 healthy subjects (18-57 y)

INTERVENTIONS

Gaboxadol 15 mg (GBX), zolpidem 10 mg (ZOL), and placebo (PBO).

MEASUREMENTS

routine polysomnographic (PSG) measures, CAP, spectral power density, and self-reported sleep measures

RESULTS

The phase advance model of transient insomnia produced significant changes in CAP parameters. Both GBX and ZOL significantly and differentially modified CAP parameters in the direction of more stable sleep. GBX brought the CAP rate in stage 1 sleep and slow wave sleep (SWS) closer to baseline levels but did not significantly change the CAP rate in stage 2. ZOL reduced the CAP rate in stage 2 to near baseline levels, whereas the CAP rate in stage 1 and SWS was reduced substantially below baseline levels. The CAP parameter A1 index (associated with SWS and sleep continuity) showed the highest correlation with self-reported sleep quality, higher than any traditional PSG, spectral, or other self-reported measures.

CONCLUSION

disruptions in CAP produced by phase advanced sleep were significantly and differentially modulated by gaboxadol and zolpidem. The relative independence of CAP parameters from other electrophysiological measures of sleep, their high sensitivity to sleep disruption, and their strong association with subjective sleep quality suggest that CAP variables may serve as valuable endpoints in future insomnia research.

Ghrelin increases slow wave sleep and stage 2 sleep and decreases stage 1 sleep and REM sleep in elderly men but does not affect sleep in elderly women

Ghrelin increases non-REM sleep and decreases REM sleep in young men but does not affect sleep in young women. In both sexes, ghrelin stimulates the activity of the somatotropic and the hypothalamic-pituitary-adrenal (HPA) axis, as indicated by increased growth hormone (GH) and cortisol plasma levels. These two endocrine axes are crucially involved in sleep regulation. As various endocrine effects are age-dependent, aim was to study ghrelin's effect on sleep and secretion of GH and cortisol in elderly humans. Sleep-EEGs (2300-0700 h) and secretion profiles of GH and cortisol (2000-0700 h) were determined in 10 elderly men (64.0+/-2.2 years) and 10 elderly, postmenopausal women (63.0+/-2.9 years) twice, receiving 50 microg ghrelin or placebo at 2200, 2300, 0000, and 0100 h, in this single-blind, randomized, cross-over study. In men, ghrelin compared to placebo was associated with significantly more stage 2 sleep (placebo: 183.3+/-6.1; ghrelin: 221.0+/-12.2 min), slow wave sleep (placebo: 33.4+/-5.1; ghrelin: 44.3+/-7.7 min) and non-REM sleep (placebo: 272.6+/-12.8; ghrelin: 318.2+/-11.0 min). Stage 1 sleep (placebo: 56.9+/-8.7; ghrelin: 50.9+/-7.6 min) and REM sleep (placebo: 71.9+/-9.1; ghrelin: 52.5+/-5.9 min) were significantly reduced. Furthermore, delta power in men was significantly higher and alpha power and beta power were significantly lower after ghrelin than after placebo injection during the first half of night. In women, no effects on sleep were observed. In both sexes, ghrelin caused comparable increases and secretion patterns of GH and cortisol. In conclusion, ghrelin affects sleep in elderly men but not women resembling findings in young subjects.

Antagonism of serotonergic 5-HT2A/2C receptors: mutual improvement of sleep, cognition and mood?

Serotonin [5-hydroxytryptamine (5-HT)] and 5-HT receptors are involved in sleep and in waking functions such as cognition and mood. Animal and human studies support a particular role for the 5-HT(2A) receptor in sleep, which has led to renewed interest in this receptor subtype as a target for the development of novel pharmacological agents to treat insomnia. Focusing primarily on findings in healthy human volunteers, a review of the available data suggests that antagonistic interaction with 5-HT(2A) receptors (and possibly also 5-HT(2C) receptors) prolongs the duration of slow wave sleep and enhances low-frequency (< 7 Hz) activity in the sleep electroencephalogram (EEG), a widely accepted marker of sleep intensity. Despite certain differences, the changes in sleep and the sleep EEG appear to be remarkably similar to those of physiologically more intense sleep after sleep deprivation. It is currently unclear whether these changes in sleep are associated with improved vigilance, cognition and mood during wakefulness. While drug-induced interaction with sleep must be interpreted cautiously, too few studies are available to provide a clear answer to this question. Moreover, functional relationships between sleep and waking functions may differ between healthy controls and patients with sleep disorders. A multimodal approach investigating subjective and objective aspects of sleep and wakefulness provides a promising research avenue for shedding light on the complex relationships among 5-HT(2A/2C) receptor-mediated effects on sleep, the sleep EEG, cognition and mood in health and various diseases associated with disturbed sleep and waking functions.

Role of GABAA receptors in the physiology and pharmacology of sleep

Most sedative-hypnotics used in insomnia treatment target the gamma-aminobutyric acid (GABA)(A) receptors. A vast repertoire of GABA(A) receptor subtypes has been identified and displays specific electrophysiological and functional properties. GABA(A)-mediated inhibition traditionally refers to 'phasic' inhibition, arising from synaptic GABA(A) receptors which transiently inhibit neurons. However, there is growing evidence that peri- or extra-synaptic GABA(A) receptors are continuously activated by low GABA concentrations and mediate a 'tonic' conductance. This slower type of signaling appears to play a key role in controlling cell excitability. This review aims at summarizing recent knowledge on GABA transmission, including the emergence of tonic conductance, and highlighting the importance of GABA(A) receptor heterogeneity. The mechanism of action of sedative-hypnotic drugs and their effects on sleep and the electroencephalogram will be reported. Furthermore, studies using genetically engineered mice will be emphasized, providing insights into the role of GABA(A) receptors in mechanisms underlying physiological and pharmacological sleep. Finally, we will address the potential of GABA(A) receptor pharmacology for the treatment of insomnia.

A 2-week efficacy and safety study of gaboxadol and zolpidem using electronic diaries in primary insomnia outpatients

OBJECTIVES

To evaluate the efficacy and safety profile of gaboxadol, a selective extrasynaptic GABA(A) agonist (SEGA) previously in development for the treatment of insomnia.

METHODS

This was a randomised, double-blind, placebo-controlled, parallel-group, 2-week, Phase III study of gaboxadol 5, 10 and 15mg in outpatients meeting the DSM-IV criteria of primary insomnia (N=742). Zolpidem 10mg was used as active reference.

RESULTS

At weeks 1 and 2, significant improvement in total sleep time (sTST) compared to placebo was seen for all doses of gaboxadol (all p<0.05). In addition, gaboxadol 10 and 15mg decreased the number of awakenings (sNAW) (p<0.05) while only gaboxadol 15mg improved wakefulness after sleep onset (sWASO) (p<0.05). At week 1, all doses of gaboxadol significantly improved time-to-sleep onset (sTSO) (p<0.05). At week 2, a sustained effect on sTSO was observed for gaboxadol 15mg. Zolpidem also showed effect on all of these variables. Gaboxadol and zolpidem improved sleep quality, freshness after sleep, daytime function and energy at both weeks. Transient rebound insomnia was observed following discontinuation of treatment with zolpidem, but not gaboxadol.

CONCLUSIONS

Gaboxadol 15mg treatment for 2 weeks significantly improved sleep onset and maintenance variables as well as sleep quality and daytime function, as did zolpidem. Gaboxadol 5 and 10mg also showed benefits on most efficacy variables. Gaboxadol was generally safe and well tolerated, with no evidence of withdrawal symptoms or rebound insomnia after discontinuation of short-term treatment. For zolpidem, transient rebound insomnia was observed.

Next-day residual effects of gaboxadol and flurazepam administered at bedtime: a randomized double-blind study in healthy elderly subjects

OBJECTIVE

To evaluate the next-day residual effects of the novel hypnotic, gaboxadol, following bedtime dosing in healthy elderly subjects.

METHODS

Healthy women (N = 15) and men (N = 10) aged 65-79 years received a single bedtime (22:00 h) dose of gaboxadol 10 mg, flurazepam 30 mg (positive control), and placebo in a randomized, double-blind, crossover study. Measures of information processing and psychomotor performance (choice reaction time, critical flicker fusion, digit symbol substitution, compensatory tracking, body sway), memory (immediate and delayed word recall), and daytime sleepiness (Multiple Sleep Latency Test), as well as subjective ratings (line analog rating scales, Leeds Sleep Evaluation Questionnaire), were obtained starting at 07:00 h the following morning. Adverse events were recorded.

RESULTS

Gaboxadol did not show next-day impairments versus placebo on any pharmacodynamic measures whereas the positive control, flurazepam, did show impairments versus placebo on most measures. Gaboxadol showed improvements versus placebo on some measures including subjective rating of next-day alertness/clumsiness on the Leeds Sleep Evaluation Questionnaire. Gaboxadol was generally well-tolerated; there were no serious adverse experiences and no subjects discontinued due to an adverse experience.

CONCLUSIONS

A single oral bedtime dose of gaboxadol 10 mg did not have next-day residual effects in healthy elderly subjects, as measured by a range of pharmacodynamic assessments, in contrast to the clear impairments produced by flurazepam 30 mg.

Slow wave sleep enhancement with gaboxadol reduces daytime sleepiness during sleep restriction

STUDY OBJECTIVES

To evaluate the impact of enhanced slow wave sleep (SWS) on behavioral, psychological, and physiological changes resulting from sleep restriction.

DESIGN

A double-blind, parallel group, placebo-controlled design was used to compare gaboxadol (GBX) 15 mg, a SWS-enhancing drug, to placebo during 4 nights of sleep restriction (5 h/night). Behavioral, psychological, and physiological measures of the impact of sleep restriction were assessed in both groups at baseline, during sleep restriction and following recovery sleep.

SETTING

Sleep research laboratory.

PARTICIPANTS

Forty-one healthy adults; 9 males and 12 females (mean age: 32.0 +/- 9.9 y) in the placebo group and 10 males and 10 females (mean age: 31.9 +/- 10.2 y) in the GBX group.

INTERVENTIONS

Both experimental groups underwent 4 nights of sleep restriction. Each group received either GBX 15 mg or placebo on all sleep restriction nights, and both groups received placebo on baseline and recovery nights.

MEASUREMENTS AND RESULTS

Polysomnography documented a SWS-enhancing effect of GBX with no group difference in total sleep time during sleep restriction. The placebo group displayed the predicted deficits due to sleep restriction on the multiple sleep latency test (MSLT) and on introspective measures of sleepiness and fatigue. Compared to placebo, the GBX group showed significantly less physiological sleepiness on the MSLT and lower levels of introspective sleepiness and fatigue during sleep restriction. There were no differences between groups on the psychomotor vigilance task (PVT) and a cognitive test battery, but these measures were minimally affected by sleep restriction in this study. The correlation between change from baseline in MSLT on Day 6 and change from baseline in SWS on Night 6 was significant in the GBX group and in both group combined.

CONCLUSIONS

The results of this study are consistent with the hypothesis that enhanced SWS, in this study produced by GBX, reduces physiological sleep tendency and introspective sleepiness and fatigue which typically result from sleep restriction.

Efficacy of the selective extrasynaptic GABAA agonist, gaboxadol, in a model of transient insomnia: A randomized, controlled clinical trial

OBJECTIVE

The hypnotic efficacy of gaboxadol, a selective extrasynaptic GABA A agonist (SEGA), was evaluated in a phase-advance model of transient insomnia.

METHODS

Healthy subjects (18-64 years) completed a randomized, double-blind, parallel group study in which the sleep period was advanced 4h from habitual sleep time. Polysomnographic (PSG) and self-reported sleep measures were used to compare gaboxadol 10mg (N =271) and 15 mg (N =274) versus placebo (N =277).

RESULTS

In the placebo group, the phase-advance procedure disrupted sleep maintenance as measured by PSG wakefulness after sleep onset (WASO) and self-reported WASO (sWASO), and also, to a lesser extent, disrupted sleep onset as measured by PSG latency to persistent sleep (LPS) and self-reported time to sleep onset (sTSO). Both doses of gaboxadol decreased WASO and sWASO versus placebo (p <or= 0.05). Gaboxadol 15 mg also reduced LPS versus placebo (p <or= 0.01) and both doses reduced sTSO versus placebo (p <or= 0.01). PSG and self-reported total sleep time as well as ratings of sleep quality were improved with both gaboxadol doses relative to placebo (all p <or= 0.01 or better). The amount of slow wave sleep (SWS) was greater with both doses of gaboxadol than with placebo (p <or= 0.001). No group differences in the amount of rapid eye movement sleep were found. Most PSG and self-report measures indicated a mild dose response. The percentage of subjects with adverse events was low (<10% in any treatment group) and all were mild or moderate; none were serious and gaboxadol did not impact morning gait or coordination.

CONCLUSIONS

Gaboxadol 10 and 15 mg were efficacious in significantly reducing the sleep maintenance and sleep onset disruption produced by this model of transient insomnia, with effects generally being most pronounced for the 15 mg dose. Gaboxadol also enhanced SWS.

Sleep-stabilizing effects of E-6199, compared to zopiclone, zolpidem and THIP in mice

Gamma aminobutyric acid (GABA)A receptor modulators constitute the majority of clinically used sedative-hypnotics. These compounds have the capacity to initiate and maintain sleep, but decrease REM sleep and delta activity within NREM sleep. In order to avoid such sleep adverse effects, the development of novel compounds remains of interest.

STUDY OBJECTIVES

The present study aimed at characterizing the acute effects of a novel putative hypnotic compound, E-6199, compared to zopiclone, zolpidem, and THIP on sleep-wakefulness patterns in mice. We also investigated whether repeated administration (daily injection during 10 days) of E-6199 was associated with tolerance and sleep disturbances at cessation of treatment.

MEASUREMENTS AND RESULTS

Polygraphic recordings were performed during 8 h after acute treatment with the various compounds. Under such conditions, E-6199 (5-20 mg/kg i.p.), zopiclone and zolpidem (2-10 mg/kg i.p.), but not THIP (2-10 mg/kg i.p.), exerted a marked sleep-promoting effect. Furthermore, E-6199 specifically increased the duration of NREM and markedly improved sleep continuity by lengthening NREM sleep episodes and reducing short awakenings and microarousal frequency. It also intensified NREM sleep by enhancing the slow wave activity within NREM at wake-NREM transitions. These effects were sustained and became even larger during chronic administration. Finally, abrupt E-6199 withdrawal did not elicit negative sleep effects.

CONCLUSIONS

Our findings demonstrate that E-6199 may be an effective hypnotic compound that promotes and improves NREMS, without producing EEG side effects, tolerance or withdrawal phenomena, when administered under chronic conditions.

Short-term treatment with gaboxadol improves sleep maintenance and enhances slow wave sleep in adult patients with primary insomnia

RATIONALE

Gaboxadol is a selective extrasynaptic GABA(A) agonist, previously in development for the treatment of insomniac patients.

OBJECTIVE

To evaluate the acute efficacy and safety of gaboxadol in primary insomnia (PI).

METHODS

This was a randomised, double-blind, four-way crossover, polysomnograph study comparing gaboxadol 10 and 20 mg (GBX20) to placebo in 40 adults with the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria for PI. Zolpidem 10 mg was used as an active reference. Treatment was administered on two consecutive nights in each treatment session. Next-day residual effects were evaluated 2 and 9 h after lights on.

RESULTS

Efficacy analysis included the per-protocol population (n = 38) from night 2. GBX20 reduced wake after sleep onset (p < 0.01). Both doses of gaboxadol, but not zolpidem, reduced the number of night awakenings (p < 0.001). GBX20 and zolpidem increased total sleep time (p < 0.05). Neither dose of gaboxadol nor zolpidem significantly reduced sleep onset latency, although a trend was seen for zolpidem. Gaboxadol enhanced slow wave sleep (SWS) dose-dependently (gaboxadol 10 mg: p < 0.01, GBX20: p < 0.001). Patients reported improved sleep quality following GBX20 (p < 0.05). Both doses of gaboxadol were generally well tolerated with almost exclusively mild to moderately severe adverse events (AEs). More frequent and severe AEs followed GBX20. No serious AEs were reported. No drug treatment was associated with next-day residual effects.

CONCLUSION

Acute administration of gaboxadol improves sleep maintenance and enhances SWS in a dose-dependent manner in adult patients with PI. Gaboxadol was not associated with next-day residual effects. Gaboxadol was generally well tolerated, although gaboxadol showed a dose-dependent increase in incidence and severity of AEs.

Neurochemical regulation of sleep

This review summarizes recent developments in the field of sleep regulation, particularly in the role of hormones, and of synthetic GABA(A) receptor agonists. Certain hormones play a specific role in sleep regulation. A reciprocal interaction of the neuropeptides growth hormone (GH)-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) plays a key role in sleep regulation. At least in males GHRH is a common stimulus of non-rapid-eye-movement sleep (NREMS) and GH and inhibits the hypothalamo-pituitary adrenocortical (HPA) hormones, whereas CRH exerts opposite effects. Furthermore CRH may enhance rapid-eye-movement sleep (REMS). Changes in the GHRH:CRH ratio in favor of CRH appear to contribute to sleep EEG and endocrine changes during depression and normal ageing. In women, however, CRH-like effects of GHRH were found. Besides CRH somatostatin impairs sleep, whereas ghrelin, galanin and neuropeptide Y promote sleep. Vasoactive intestinal polypeptide appears to be involved in the temporal organization of human sleep. Beside of peptides, steroids participate in sleep regulation. Cortisol appears to promote REMS. Various neuroactive steroids exert specific effects on sleep. The beneficial effect of estrogen replacement therapy in menopausal women suggests a role of estrogen in sleep regulation. The GABA(A) receptor or GABAergic neurons are involved in the action of many of these hormones. Recently synthetic GABA(A) agonists, particularly gaboxadol and the GABA reuptake inhibitor tiagabine were shown to differ distinctly in their action from allosteric modulators of the GABA(A) receptor like benzodiazepines as they promote slow-wave sleep, decrease wakefulness and do not affect REMS.

The EEG effects of THIP (Gaboxadol) on sleep and waking are mediated by the GABA(A)delta-subunit-containing receptors

THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol, Gaboxadol) is a selective gamma-aminobutyric acid (GABA)(A) agonist, acting in vitro with high potency and efficacy at the extrasynaptic GABA(A)delta-containing receptors. THIP was suggested to be a potential hypnotic to treat insomnia, and it is currently in clinical trial. Here we assessed whether the GABA(A)delta-containing receptors mediate in vivo the effect of THIP on sleep and the sleep electroencephalogram (EEG). We performed EEG recordings in a mouse model deficient in the GABA(A)delta-subunit gene (delta(-/-) mice) and in wild-type littermate controls. THIP (4 and 6 mg/kg intraperitoneally) induced an abnormal EEG pattern, resulting in dramatic changes in the waking and non-rapid eye movement (NREM) sleep EEG spectra in wild-type mice. Indeed, a massive increase in EEG power lasting 2-3 h occurred in both the frontal and parietal derivation, especially in frequencies below 6 Hz. All effects were more prominent in the frontal EEG. Furthermore, the highest dose of THIP lengthened REM sleep latency and suppressed REM sleep. In contrast, vigilance states and sleep latencies were not affected in delta(-/-) mice. Moreover, only minor changes were observed in the NREM sleep EEG spectrum after THIP injection in the delta-subunit-deficient mice. The present findings do not indicate a sleep-promoting effect of THIP in mice, which is in accordance with a previous report in this species. Moreover, our results in vivo demonstrate that THIP acts preferentially at GABA(A) receptors containing the delta-subunit.

Treating insomnia: Current and investigational pharmacological approaches

Chronic insomnia affects a significant proportion of young adult and elderly populations. Treatment strategies should alleviate nighttime symptoms, the feeling of nonrestorative sleep, and impaired daytime function. Current pharmacological approaches focus primarily on GABA, the major inhibitory neurotransmitter in the central nervous system. Benzodiazepine receptor agonists (BzRA) have been a mainstay of pharmacotherapy; the classical benzodiazepines and non-benzodiazepines share a similar mode of action and allosterically enhance inhibitory chloride currents through the GABA(A) receptor, a ligand-gated protein comprising 5 subunits pseudosymmetrically arranged around a core anion channel. Variations in GABA(A) receptor subunit composition confer unique pharmacological, biophysical, and electrophysiological properties on each receptor subtype. Classical benzodiazepines bind non-selectively to GABA(A) receptors containing a gamma2 subunit, whereas non-benzodiazepine hypnotics bind with higher relative affinity to alpha1-containing receptors. The non-benzodiazepine compounds generally represent an improvement over benzodiazepines as a result of improved binding selectivity and pharmacokinetic profiles. However, the enduring potential for amnestic effects, next day residual sedation, and abuse and physical dependence, particularly at higher doses, underscores the need for new treatment strategies. Novel pharmacotherapies in development act on systems believed to be specifically involved in the regulation of the sleep-wake cycle. The recently approved melatonin receptor agonist, ramelteon, targets circadian mechanisms. Gaboxadol, an investigational treatment and a selective extrasynaptic GABA(A) receptor agonist (SEGA), targets GABA(A) receptors containing a delta subunit, which are located outside the synaptic junctions of thalamic and cortical neurons thought to play an important regulatory role in the onset, maintenance, and depth of the sleep process.

GABAA receptor alpha 4 subunits mediate extrasynaptic inhibition in thalamus and dentate gyrus and the action of gaboxadol

The neurotransmitter GABA mediates the majority of rapid inhibition in the CNS. Inhibition can occur via the conventional mechanism, the transient activation of subsynaptic GABAA receptors (GABAA-Rs), or via continuous activation of high-affinity receptors by low concentrations of ambient GABA, leading to "tonic" inhibition that can control levels of excitability and network activity. The GABAA-R alpha4 subunit is expressed at high levels in the dentate gyrus and thalamus and is suspected to contribute to extrasynaptic GABAA-R-mediated tonic inhibition. Mice were engineered to lack the alpha4 subunit by targeted disruption of the Gabra4 gene. alpha4 Subunit knockout mice are viable, breed normally, and are superficially indistinguishable from WT mice. In electrophysiological recordings, these mice show a lack of tonic inhibition in dentate granule cells and thalamic relay neurons. Behaviorally, knockout mice are insensitive to the ataxic, sedative, and analgesic effects of the novel hypnotic drug, gaboxadol. These data demonstrate that tonic inhibition in dentate granule cells and thalamic relay neurons is mediated by extrasynaptic GABAA-Rs containing the alpha4 subunit and that gaboxadol achieves its effects via the activation of this GABAA-R subtype.

Emerging pharmacotherapeutic agents for insomnia: a hypnotic panacea?

The burden of insomnia has had a significant effect not only on the socioeconomic matrix, but also the medical terrain, as signified by the increased morbidity and mortality of its associated psychiatric and organic sequelae. To this end, a plethora of pharmacotherapeutic agents have been recently introduced that address the vital need to combat insomnia and prevent the perpetuation in its chronic form. The previously and currently dispensed barbiturates and benzodiazepines, respectively, have paved the way for newer agents that are purported to be just as effective, or even more so, with a favourable profile in all domains of sleep. In assessing both published clinical studies and unpublished reports conducted on these emerging agents, this article profiles the most contemporary, therapeutic options in lieu of older hypnotics, over-the-counter medications and supplements. Furthermore, this paper aims to indicate both the future course of hypnotics and the developments currently in progress.

Eszopiclone

PURPOSE

The pharmacology, pharmacokinetics, indications, clinical efficacy, adverse effects, drug interactions, dosing, and administration of eszopiclone are discussed.

SUMMARY

The pharmacology of eszopiclone is not well understood. Eszopiclone is the S-isomer of racemic zopiclone. The relative bioavailability of oral racemic zopiclone is about 80%. Eszopiclone is rapidly absorbed after oral administration, with peak serum concentrations ranging from 1 to 1.3 hours. The efficacy of eszopiclone has been evaluated in healthy adults, including elderly patients, for the treatment of transient and chronic insomnia. Compared with placebo, eszopiclone has been shown to considerably reduce sleep induction and improve sleep maintenance, duration, quality, and depth, as well as next-day functioning. The most common adverse effects reported are unpleasant taste, headache, and dry mouth. Dosing should be individualized, and the lowest effective dose should be used to minimize the risk of adverse events. The recommended starting dosage for nonelderly patients is 2 mg immediately before bedtime, with adjustment to 3 mg if clinically indicated. Dosage adjustment is necessary in patients with severe hepatic disease and in those receiving concomitant potent cytochrome P-450 isoenzyme 3A4 inhibitors. No dosage adjustment is required for patients with renal dysfunction. The cost of eszopiclone is 3.70 dollars per tablet for all dosage strengths (1-, 2-, and 3-mg tablets).

CONCLUSION

Its favorable adverse-effect profile and approved labeling for the treatment of chronic insomnia makes eszopiclone a viable alternative for insomnia treatment. Published data are limited, however, and more clinical trials, including comparator studies, are needed to further evaluate the use of this drug.

Treatment of sleep disorders in elderly patients

Sleep disorders are common among the elderly and are associated with diminished quality of life, increased risk for development of psychiatric disorders, inappropriate use of sleep aids, and decreased daytime functioning. The most common and important sleep disorders in the elderly include insomnia, obstructive sleep apnea syndrome, restless legs syndrome, rapid eye movement sleep behavior disorder, and the advanced sleep phase syndrome. In this article, we summarize the current treatment strategies for each of these sleep-related disorders. Before contemplating specific treatments, the authors recommend that more conservative and nonpharmacologic therapies be attempted first because the elderly are more likely to have medication side effects or complications related to surgery. Many sleep problems can be treated by simple sleep hygiene modifications that can be implemented and adopted easily. For others, therapies that specifically consider older adults may be required. For each of the sleep disorders we provide an updated discussion of therapies beginning with diet and lifestyle, pharmacologic treatment, interventional procedures, surgery, assistive devices, physical and speech therapy, exercise, and emerging therapies with specific considerations for older adults.

GABA(A) receptor subtypes as targets for neuropsychiatric drug development

The main inhibitory neurotransmitter system in the brain, the gamma-aminobutyric acid (GABA) system, is the target for many clinically used drugs to treat, for example, anxiety disorders and epilepsy and to induce sedation and anesthesia. These drugs facilitate the function of pentameric A-type GABA (GABA(A)) receptors that are extremely widespread in the brain and composed from the repertoire of 19 subunit variants. Modern genetic studies have found associations of various subunit gene polymorphisms with neuropsychiatric disorders, including alcoholism, schizophrenia, anxiety, and bipolar affective disorder, but these studies are still at their early phase because they still have failed to lead to validated drug development targets. Recent neurobiological studies on new animal models and receptor subunit mutations have revealed novel aspects of the GABA(A) receptors, which might allow selective targeting of the drug action in receptor subtype-selective fashion, either on the synaptic or extrasynaptic receptor populations. More precisely, the greatest advances have occurred in the clarification of the molecular and behavioral mechanisms of action of the GABA(A) receptor agonists already in the clinical use, such as benzodiazepines and anesthetics, rather than in the introduction of novel compounds to clinical practice. It is likely that these new developments will help to overcome the present problems of the chronic treatment with nonselective GABA(A) agonists, that is, the development of tolerance and dependence, and to focus the drug action on the neurobiologically and neuropathologically relevant substrates.