Opioid inhibition of rapid eye movement sleep by a specific mu receptor agonist

Insomnia-related rodent models in drug discovery

Despite the widespread prevalence and important medical impact of insomnia, effective agents with few side effects are lacking in clinics. This is most likely due to relatively poor understanding of the etiology and pathophysiology of insomnia, and the lack of appropriate animal models for screening new compounds. As the main homeostatic, circadian, and neurochemical modulations of sleep remain essentially similar between humans and rodents, rodent models are often used to elucidate the mechanisms of insomnia and to develop novel therapeutic targets. In this article, we focus on several rodent models of insomnia induced by stress, diseases, drugs, disruption of the circadian clock, and other means such as genetic manipulation of specific neuronal activity, respectively, which could be used to screen for novel hypnotics. Moreover, important advantages and constraints of some animal models are discussed. Finally, this review highlights that the rodent models of insomnia may play a crucial role in novel drug development to optimize the management of insomnia.

S-Ketamine Improves Slow Wave Sleep and the Associated Changes in Serum Protein Among Gynecological Abdominal Surgery Patients: A Randomized Controlled Trial

Purpose

This study aims to evaluate the effect of S-ketamine on slow wave sleep (SWS) and the related changes in serum protein in gynecological patients after open abdomen surgery.

Methods

This was a randomized controlled trial. One hundred gynecological patients undergoing open abdomen surgery were randomized into an S-ketamine group (group S) or placebo group (0.9% saline; group C). During operation, patients in group S received adjuvant S-ketamine infusion (0.2 mg·kg-1·h-1) while those in group C received 0.9% saline. All patients were connected to patient-controlled intravenous analgesia (PCIA) pump in the end of the surgery and the patients in group S with an additional S-ketamine in PCIA pump. Polysomnogram (PSG) was monitored during the next night after surgery with PCIA pump. Blood samples were collected for proteomic analysis at 6:00 AM after PSG monitoring. The primary outcome was the percentage of SWS (also known as stage 3 non-rapid eye movement sleep, stage N3) on the next night after surgery, and the secondary outcome was subjective sleep quality, pain scores, and the changes in serum proteomics.

Results

Complete polysomnogram recordings were obtained from 64 study participants (31 in group C and 33 in group S). The administration of S-ketamine infusion resulted in a significant increase in the percentage of SWS/N3 compared to the control group (group C, median (IQR [range]), 8.9 (6.3, 12.5); group S, median (IQR [range]), 15.6 (12.4, 18.8), P<0.001). However, subjective evaluations of sleep quality revealed no significant variances between the two groups. The protein affected by S-ketamine was primarily associated with posttranslational modification, protein turnover, carbohydrate transport, and metabolism.

Conclusion

In patients undergoing open gynecological surgery, S-ketamine enhanced the percentage of objective sleep of SWS during the next night after surgery. Additionally, there were differences observed in serum protein levels between the two groups.

Trial Registration

ChiCTR2200055180. Registered on 02/01/2022.

Identification of Factors Contributing to Methadone-Induced Daytime Sleepiness in Cancer Patients and Proposal of the Conversion Ratio from Other Opioids to Oral Methadone: A Retrospective Cohort Study

Background

When methadone is used to treat cancer pain, the Japanese health insurance system recommends to determine the starting dose according to the equivalency conversion table based on the morphine-equivalent daily dose (MEDD) of prior opioids proposed by the National Comprehensive Cancer Network. Owing to the wide range in variability of the conversion table, methadone increases the incidence of daytime sleepiness.

Objective

To identify the factors associated with daytime sleepiness and propose a conversion ratio from pretreatment MEDD to oral methadone that decreases the risk of daytime sleepiness.

Design

Retrospective cohort study.

Setting/Subjects

One hundred patients who started oral methadone to relieve cancer pain at Ashiya Municipal Hospital (Hyogo, Japan) from January 1, 2013, to August 31, 2022, were enrolled.

Measurements

The primary endpoint, the conversion ratio from pretreatment MEDD to oral methadone without daytime sleepiness, was determined using receiver operator characteristic (ROC) curve analysis.

Results

The incidence of daytime sleepiness within seven days of methadone initiation was 40.0%. The factors identified as contributing to daytime sleepiness were pretreatment MEDD (odds ratio [OR]: 0.941, 95% confidence interval [CI]: 0.916-0.966, p <0.001) and methadone dose (OR: 1.395, 95% CI: 1.178-1.652, p <0.001). The conversion ratio from pretreatment MEDD to oral methadone was 0.24, with an area under the ROC curve of 0.909 (p <0.001).

Conclusions

Daytime sleepiness developed when methadone dose is high relative to pretreatment MEDD. To the best of our knowledge, this is the first study to suggest the conversion ratio from pretreatment MEDD to oral methadone without causing daytime sleepiness.

Sleep during and following critical illness: A narrative review

Sleep is a complex process influenced by biological and environmental factors. Disturbances of sleep quantity and quality occur frequently in the critically ill and remain prevalent in survivors for at least 12 mo. Sleep disturbances are associated with adverse outcomes across multiple organ systems but are most strongly linked to delirium and cognitive impairment. This review will outline the predisposing and precipitating factors for sleep disturbance, categorised into patient, environmental and treatment-related factors. The objective and subjective methodologies used to quantify sleep during critical illness will be reviewed. While polysomnography remains the gold-standard, its use in the critical care setting still presents many barriers. Other methodologies are needed to better understand the pathophysiology, epidemiology and treatment of sleep disturbance in this population. Subjective outcome measures, including the Richards-Campbell Sleep Questionnaire, are still required for trials involving a greater number of patients and provide valuable insight into patients’ experiences of disturbed sleep. Finally, sleep optimisation strategies are reviewed, including intervention bundles, ambient noise and light reduction, quiet time, and the use of ear plugs and eye masks. While drugs to improve sleep are frequently prescribed to patients in the ICU, evidence supporting their effectiveness is lacking.

Influence of general anesthesia on the postoperative sleep cycle in patients undergoing surgery and dental treatment: a scoping review on the incidence of postoperative sleep disturbance

General anesthesia may influence the postoperative sleep cycle; however, no clinical studies have fully evaluated whether anesthesia causes sleep disturbances during the postoperative period. In this scoping review, we explored the changes in postoperative sleep cycles during surgical procedures or dental treatment under general anesthesia. We compared and evaluated the influence of general anesthesia on sleep cycles and sleep disturbances during the postoperative period in adult and pediatric patients undergoing surgery and/or dental treatment. Literature was retrieved by searching eight public databases. Randomized clinical trials, observational studies, observational case-control studies, and cohort studies were included. Primary outcomes included the incidence of sleep, circadian cycle alterations, and/or sleep disturbances. The search strategy yielded six studies after duplicates were removed. Finally, six clinical trials with 1,044 patients were included. In conclusion, general anesthesia may cause sleep disturbances based on alterations in sleep or the circadian cycle in the postoperative period in patients scheduled for elective surgery.

Sleep disturbance as a therapeutic target to improve opioid use disorder treatment

Sleep health is an important factor across several physical and mental health disorders, and a growing scientific consensus has identified sleep as a critical component of opioid use disorder (OUD), both in the active disease state and during OUD recovery. The goal of this narrative review is to collate the literature on sleep, opioid use, and OUD as a means of identifying therapeutic targets to improve OUD treatment outcomes. Sleep disturbance is common and often severe in persons with OUD, especially during opioid withdrawal, but also in persons on opioid maintenance therapies. There is ample evidence that sleep disturbances including reduced total sleep time, disrupted sleep continuity, and poor sleep quality often accompany negative OUD treatment outcomes. Sleep disturbances are bidirectionally associated with several other factors related to negative treatment outcomes, including chronic stress, stress reactivity, low positive affect, high negative affect, chronic pain, and drug craving. This constellation of outcome variables represents a more comprehensive appraisal of the quality of life and quality of recovery than is typically assessed in OUD clinical trials. To date, there are very few clinical trials or experimental studies aimed at improving sleep health in OUD patients, either as a means of improving stress, affect, and craving outcomes, or as a potential mechanistic target to reduce opioid withdrawal and drug use behaviors. As such, the direct impact of sleep improvement in OUD patients is largely unknown, yet mechanistic and clinical research suggests that therapeutic interventions that target sleep are a promising avenue to improve OUD treatment. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Pediatric sleep and pain: etiologies, consequences, and clinical considerations

STUDY OBJECTIVES

To examine current evidence of the relationship between sleep and pain from the neonatal period through adolescence. This review serves as a critical review of the literature and of the needs for future research on pediatric sleep and pain.

METHODS

The PubMed online database was queried from January 1, 1960, to March 1, 2020, producing 149 articles applicable to pain and sleep in the pediatric population. Of those, 97 articles were cited in this review with the key articles including over 3800 participants.

RESULTS

The pediatric literature supports the relationship between poor sleep (both sleep efficiency and nighttime awakenings) and subsequent risk for pain, especially among children with chronic disease. The reverse effect of pain on sleep is not yet well delineated. The key moderating factors explored in the literature are pharmacologic and nonpharmacologic therapies, psychologic health, and the etiology of pain. There is evidence that both altered sleep and pain early in life impact neurodevelopment, as seen by changes in sleep structure in clinical studies and alterations in brain development in animal models.

CONCLUSIONS

The complicated relationship between sleep and pain is critically important during pediatric development when alterations to a normal sleep structure can have a lifelong impact. It is becoming clear that sleep deprivation and poor sleep quality exacerbate pain. Further research is needed into the complex alterations of sleep in chronic pain conditions as well as treatments to improve sleep in pediatric care.

CITATION

Morris EE, Howell MJ, Pickup E, Iber C, Wang SG. Pediatric sleep and pain: etiologies, consequences, and clinical considerations. J Clin Sleep Med. 2022;18(9):2281-2289.

Is There Any Role for Opioids in the Management of Knee and Hip Osteoarthritis? A Systematic Review and Meta-Analysis

OBJECTIVE

Opioids have long been prescribed for chronic pain conditions, including osteoarthritis (OA). However, there is little information about their temporal efficacy, or differences in efficacy and safety between opioids with strong versus weak/intermediate μ opioid receptor-binding affinity. To explore these research questions, we conducted a systematic review and meta-analyses of randomized controlled trials (RCTs) conducted in patients with knee and/or hip OA.

METHODS

We searched Medline, Embase, PubMed Central, and the Cochrane Central Register of Controlled Trials from inception to December 2019 and sought unpublished data. Placebo-controlled RCTs of oral opioids in patients with knee and/or hip OA were included. Standardized mean differences (SMDs) were calculated for pain and function at 2, 4, 8, and 12 weeks. Subgroup analyses for strong and weak/intermediate opioids were conducted. Meta-regression was performed to assess the impact of dosage (morphine equivalency) on pain relief. Risk ratios were calculated for safety at the final follow-up.

RESULTS

A total of 18 RCTs (9,283 participants) were included. Opioids demonstrated small benefits on pain at each time point, with SMDs ranging from -0.28 (95% confidence interval [95% CI] -0.38, -0.17) to -0.19 (95% CI -0.29, -0.08); similar effects were observed for function. Strong opioids demonstrated consistently inferior efficacy and overall worse safety than weak/intermediate opioids. Meta-regression revealed that incremental pain relief achieved beyond 20-50-mg doses was not substantial in the context of increased safety risks.

CONCLUSION

Opioids provide minimal relief of OA symptoms within a 12-week period, and they are known to cause discomfort in a majority of patients. Clinicians and policy makers should reconsider the utility of opioids in the management of OA.

Why It Is Important to Consider the Effects of Analgesics on Sleep: A Critical Review

We review the known physiological mechanisms underpinning all of pain processing, sleep regulation, and pharmacology of analgesics prescribed for chronic pain. In particular, we describe how commonly prescribed analgesics act in sleep-wake neural pathways, with potential unintended impact on sleep and/or wake function. Sleep disruption, whether pain- or drug-induced, negatively impacts quality of life, mental and physical health. In the context of chronic pain, poor sleep quality heightens pain sensitivity and may affect analgesic function, potentially resulting in further analgesic need. Clinicians already have to consider factors including efficacy, abuse potential, and likely side effects when making analgesic prescribing choices. We propose that analgesic-related sleep disruption should also be considered. The neurochemical mechanisms underlying the reciprocal relationship between pain and sleep are poorly understood, and studies investigating sleep in those with specific chronic pain conditions (including those with comorbidities) are lacking. We emphasize the importance of further work to clarify the effects (intended and unintended) of each analgesic class to inform personalized treatment decisions in patients with chronic pain. © 2021 American Physiological Society. Compr Physiol 11:1-31, 2021.

Bidirectional Relationship between Opioids and Disrupted Sleep: Putative Mechanisms

Millions of Americans suffer from opiate use disorder, and over 100 die every day from opioid overdoses. Opioid use often progresses into a vicious cycle of abuse and withdrawal, resulting in very high rates of relapse. Although the physical and psychologic symptoms of opiate withdrawal are well-documented, sleep disturbances caused by chronic opioid exposure and withdrawal are less well-understood. These substances can significantly disrupt sleep acutely and in the long term. Yet poor sleep may influence opiate use, suggesting a bidirectional feed-forward interaction between poor sleep and opioid use. The neurobiology of how opioids affect sleep and how disrupted sleep affects opioid use is not well-understood. Here, we will summarize what is known about the effects of opioids on electroencephalographic sleep in humans and in animal models. We then discuss the neurobiology interface between reward-related brain regions that mediate arousal and wakefulness as well as the effect of opioids in sleep-related brain regions and neurotransmitter systems. Finally, we summarize what is known of the mechanisms underlying opioid exposure and sleep. A critical review of such studies, as well as recommendations of studies that evaluate the impact of manipulating sleep during withdrawal, will further our understanding of the cyclical feedback between sleep and opioid use. SIGNIFICANCE STATEMENT: We review recent studies on the mechanisms linking opioids and sleep. Opioids affect sleep, and sleep affects opioid use; however, the biology underlying this relationship is not understood. This review compiles recent studies in this area that fill this gap in knowledge.

Correlates of sleep quality and excessive daytime sleepiness in people with opioid use disorder receiving methadone treatment

PURPOSE

The aim of this study was to evaluate the prevalence and clinical correlates of impaired sleep quality and excessive daytime sleepiness among patients receiving methadone for opioid use disorder (OUD).

METHODS

Patients receiving methadone (n = 164) completed surveys assessing sleep quality (Pittsburgh Sleep Quality Index [PSQI]), daytime sleepiness (Epworth Sleepiness Scale [ESS]), and related comorbidities. We used bivariate and multivariable linear regression models to evaluate correlates of sleep quality and daytime sleepiness.

RESULTS

Ninety percent of patients had poor sleep quality (PSQI >5), and the mean PSQI was high (11.0 ±4). Forty-six percent reported excessive daytime sleepiness (ESS > 10). In multivariable analyses, higher PSQI (worse sleep quality) was significantly associated with pain interference (coefficient = 0.40; 95% CI = 0.18-0.62; β = 0.31), somatization (coefficient = 2.2; 95% CI = 0.75-3.6; β = 0.26), and negatively associated with employment (coefficient = - 2.6; 95% CI = - 4.9 to - 0.19; β = - 0.17). Greater sleepiness was significantly associated with body mass index (coefficient = 0.32; 95% CI = 0.18-0.46; β = 0.33), and there was a non-significant association between sleepiness and current chronic pain (coefficient = 1.6; 95% CI = 0.26-3.5; β = 0.13; p value = 0.09).

CONCLUSIONS

Poor sleep quality and excessive daytime sleepiness are common in patients receiving methadone for OUD. Chronic pain, somatization, employment status, and obesity are potentially modifiable risk factors for sleep problems for individuals maintained on methadone. People with OUD receiving methadone should be routinely and promptly evaluated and treated for sleep disorders.

Alcohol use disorder and sleep disturbances: a feed-forward allostatic framework

The development of alcohol use disorder (AUD) involves binge or heavy drinking to high levels of intoxication that leads to compulsive intake, the loss of control in limiting intake, and a negative emotional state when alcohol is removed. This cascade of events occurs over an extended period within a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. These three heuristic stages map onto the dysregulation of functional domains of incentive salience/habits, negative emotional states, and executive function, mediated by the basal ganglia, extended amygdala, and frontal cortex, respectively. Sleep disturbances, alterations of sleep architecture, and the development of insomnia are ubiquitous in AUD and also map onto the three stages of the addiction cycle. During the binge/intoxication stage, alcohol intoxication leads to a faster sleep onset, but sleep quality is poor relative to nights when no alcohol is consumed. The reduction of sleep onset latency and increase in wakefulness later in the night may be related to the acute effects of alcohol on GABAergic systems that are associated with sleep regulation and the effects on brain incentive salience systems, such as dopamine. During the withdrawal/negative affect stage, there is a decrease in slow-wave sleep and some limited recovery in REM sleep when individuals with AUD stop drinking. Limited recovery of sleep disturbances is seen in AUD within the first 30 days of abstinence. The effects of withdrawal on sleep may be related to the loss of alcohol as a positive allosteric modulator of GABAA receptors, a decrease in dopamine function, and the overactivation of stress neuromodulators, including hypocretin/orexin, norepinephrine, corticotropin-releasing factor, and cytokines. During the preoccupation/anticipation stage, individuals with AUD who are abstinent long-term present persistent sleep disturbances, including a longer latency to fall asleep, more time awake during the night, a decrease in slow-wave sleep, decreases in delta electroencephalogram power and evoked delta activity, and an increase in REM sleep. Glutamatergic system dysregulation that is observed in AUD is a likely substrate for some of these persistent sleep disturbances. Sleep pathology contributes to AUD pathology, and vice versa, possibly as a feed-forward drive to an unrecognized allostatic load that drives the addiction process.

Sleep and the Pharmacotherapy of Alcohol Use Disorder: Unfortunate Bedfellows. A Systematic Review With Meta-Analysis

Background: Sleep disorders are commonly associated with acute and chronic use of alcohol and with abstinence. To date, there are four approved drugs to treat alcohol use disorder (AUD): disulfiram, acamprosate, naltrexone, and nalmefene. These AUD therapies reduce the craving and risk of relapse into heavy drinking, but little is known about their effect on sleep. As recent evidences indicate a crucial role of sleep disorders in AUD, claiming that sleep problems may trigger alcohol abuse and relapses, it is fundamental to clarify the impact of those drugs on the sleep quality of AUD patients. This systematic review aims to answer the question: how does the pharmacotherapy for AUD affect sleep? Methods: We searched PubMed, Embase, CINAHL Plus, Cochrane, and Scopus using sleep- and AUD pharmacotherapy-related keywords. The articles included were appraised using the CASP checklists, and the risk of bias was assessed following the Cochrane risk-of-bias assessment tool. Finally, we pooled sleep outcomes in a meta-analysis to measure the overall effect. Results and Conclusion: We included 26 studies: only three studies focused on sleep as a main outcome, two with polysomnography (objective measurement), and one with subjective self-reported sleep, while all the other studies reported sleep problems among the adverse effects (subjective report). The only study available on disulfiram showed reduced REM sleep. Acamprosate showed no/little effect on self-reported sleep but improved sleep continuity and architecture measured by polysomnography. The two opioidergic drugs naltrexone and nalmefene had mainly detrimental effect on sleep, giving increased insomnia and/or somnolence compared with placebo, although not always significant. The meta-analysis confirmed significantly increased somnolence and insomnia in the naltrexone group, compared with the placebo. Overall, the currently available evidences show more sleep problems with the opioidergic drugs (especially naltrexone), while acamprosate seems to be well tolerated or even beneficial. Acamprosate might be a more suitable choice when patients with AUD report sleep problems. Due to the paucity of information available, and with the majority of results being subjective, more research on this topic is needed to further inform the clinical practice, ideally with more objective measurements such as polysomnography.

Electrocortical changes associating sedation and respiratory depression by the opioid analgesic fentanyl

Opioid drugs are the mainstay of pain management but present the side-effect of respiratory depression that can be lethal with overdose. In addition to their respiratory effect, opioids also induce a profound sedative state and produce electrocortical features characteristic of a state of reduced brain arousal, similar to anaesthesia or sleep. In such states, respiratory activity depends more on the integrity of the brainstem respiratory network than it does during wakefulness. Accordingly, we propose that sedation by fentanyl induces specific electrocortical changes consistent with reduced brain arousal, and that the magnitude of respiratory depression is associated with distinct electrocortical changes. To these aims, we determined the effects of systemic injections of fentanyl (dosage 100 µg ·kg) versus control on electrocortical  and respiratory activities of freely-behaving rats. We found that fentanyl induced electrocortical changes that differed from those observed in sleep or wakefulness. Fentanyl increased δ (1-3 Hz) frequency power (P < 0.001), but reduced α (7.5-13.5 Hz) and β2 (20-30 Hz) powers (P = 0.012 and P < 0.001, respectively), when compared to wakefulness. Interestingly, respiratory rate depression by fentanyl was significantly correlated with increased θ power (R = 0.61, P < 0.001), therefore showing a clear association between electrocortical activity and the magnitude of respiratory rate depression. Overall, we provide new evidence linking specific electrocortical changes to the severity of respiratory depression by opioids, which highlights the importance of considering the cortical and subcortical effects of opioids in addition to their impacts on breathing when evaluating opioid-induced respiratory depression.

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Visual vertigo: Vertigo of oculomotor origin

Since Róbert Bárány proposed his hypothesis on vestibulo-ocular reflex (VOR), dizziness associated with vertigo has been interpreted as being vestibular in origin. However, there have been many contradictory findings showing modulations of VOR, which have caused confusion as to VOR's role and accuracy. Further, there seems to be an influence of VOR when the anatomical inner ear structures are congenitally absent. Many people report vertiginous symptoms when they are exposed to visually challenging situations. These people with visually induced vertigo are usually found to have only mildly abnormal labyrinthine findings. Accurate visual information via binocular vision in animals, including humans, is important for the survival. Understanding how visual information is used in balance can help us to apply a different approach to the mechanism of vertigo. This article will review how accurate binocular viewing is possible for precise images through a complex oculomotor system and the proprioceptive senses of the external ocular muscles (EOMs). The proprioceptive senses from EOMs appear to affect motor efferents of the body. Oculomotor activities during viewing are important not just for learning but also for executing whole body motor responses. An error in the oculomotor afferents will cause a reaction to the error signal. This can be troubling for proper balancing during movement. Especially, common oculomotor causes (including fatigue of EOMs which is common in today's lifestyle) can contribute to many vertiginous conditions.

Buprenorphine Depresses Respiratory Variability in Obese Mice with Altered Leptin Signaling

BACKGROUND

Opiate-induced respiratory depression is sexually dimorphic and associated with increased risk among the obese. The mechanisms underlying these associations are unknown. The present study evaluated the two-tailed hypothesis that sex, leptin status, and obesity modulate buprenorphine-induced changes in breathing.

METHODS

Mice (n = 40 male and 40 female) comprising four congenic lines that differ in leptin signaling and body weight were injected with saline and buprenorphine (0.3 mg/kg). Whole-body plethysmography was used to quantify the effects on minute ventilation. The data were evaluated using three-way analysis of variance, regression, and Poincaré analyses.

RESULTS

Relative to B6 mice with normal leptin, buprenorphine decreased minute ventilation in mice with diet-induced obesity (37.2%; P < 0.0001), ob/ob mice that lack leptin (62.6%; P < 0.0001), and db/db mice with dysfunctional leptin receptors (65.9%; P < 0.0001). Poincaré analyses showed that buprenorphine caused a significant (P < 0.0001) collapse in minute ventilation variability that was greatest in mice with leptin dysfunction. There was no significant effect of sex or body weight on minute ventilation.

CONCLUSIONS

The results support the interpretation that leptin status but not body weight or sex contributed to the buprenorphine-induced decrease in minute ventilation. Poincaré plots illustrate that the buprenorphine-induced decrease in minute ventilation variability was greatest in mice with impaired leptin signaling. This is relevant because normal respiratory variability is essential for martialing a compensatory response to ventilatory challenges imposed by disease, obesity, and surgical stress.

Frequency and correlates of sleep disturbance in methadone and buprenorphine-maintained patients

BACKGROUND

Opioid use disorder (OUD) is a significant public health problem, and opioid maintenance treatment (OMT) on methadone or buprenorphine is a common approach. This study characterized sleep impairment in patients maintained on methadone or buprenorphine, and evaluated its association with psychiatric and medical comorbidities.

METHODS

Participants (N=185) maintained on methadone (N=125) or buprenorphine (N=60) for OUD completed the Medical Outcomes Study Sleep Scale (MOS) to provide a point-prevalence assessment of sleep impairment. Measures of lifetime problems and current functioning were also examined and compared as both a function of OMT and level of sleep impairment.

RESULTS

Participants reported high levels of sleep impairment on the MOS, including not getting the amount of sleep they needed (42.9%), not sleeping enough to feel rested (39.6%) and trouble falling asleep (23.3%) or falling back asleep after waking (25.8%). Few differences were observed between OMT groups, and psychiatric dysfunction emerged as the most robust predictor of sleep impairment ratings. Patients with sleep impairment, independent of OMT medications, also reported current opioid withdrawal, psychiatric impairment, negative affect, and pain.

CONCLUSIONS

Results demonstrate substantial and clinically-significant impairments in sleep that are associated with a variety of current problems that could impact OMT outcomes and decrease quality of life. Outcomes support the development of methods to improve sleep in OMT patients, and to examine the degree to which sleep improvements may be associated with improvements in mood and other health-related measures.

Obstructive sleep apnea, pain, and opioids: is the riddle solved?

PURPOSE OF REVIEW

Perioperative opioid-based pain management of patients suffering from obstructive sleep apnea (OSA) may present challenges because of concerns over severe ventilatory compromise. The interaction between intermittent hypoxia, sleep fragmentation, pain, and opioid responses in OSA, is complex and warrants a special focus of perioperative outcomes research.

RECENT FINDINGS

Life-threatening opioid-related respiratory events are rare. Epidemiologic evidence suggests that OSA together with other serious renal and heart disease, is among those conditions predisposing patients for opioid-induced ventilatory impairment (OIVI) in the postoperative period. Both intermittent hypoxia and sleep fragmentation, two distinct components of OSA, enhance pain. Intermittent hypoxia may also potentiate opioid analgesic effects. Activation of major inflammatory pathways may be responsible for the effects of sleep disruption and intermittent hypoxia on pain and opioid analgesia. Recent experimental evidence supports that these, seemingly contrasting, phenotypes of pain-increasing and opioid-enhancing effects of intermittent hypoxia, are not mutually exclusive. Although the effect of intermittent hypoxia on OIVI has not been elucidated, opioids worsen postoperative sleep-disordered breathing in OSA patients. A subset of these patients, characterized by decreased chemoreflex responsiveness and high arousal thresholds, might be at higher risk for OIVI.

SUMMARY

OSA may complicate opioid-based perioperative management of pain by altering both pain processing and sensitivity to opioid effect.

Effect of sedative-hypnotics, anesthetics and analgesics on sleep architecture in obstructive sleep apnea

The perioperative care of obstructive sleep apnea (OSA) patients is currently receiving much attention due to an increased risk for complications. It is established that postoperative changes in sleep architecture occur and this may have pathophysiological implications for OSA patients. Upper airway muscle activity decreases during rapid eye movement sleep (REMS). Severe OSA patients exhibit exaggerated chemoreceptor-driven ventilation during non-rapid eye movement sleep (NREMS), which leads to central and obstructive apnea. This article critically reviewed the literature relevant to preoperative screening for OSA, prevalence of OSA in surgical populations and changes in postoperative sleep architecture relevant to OSA patients. In particular, we addressed three questions in regard to the effects of sedative-hypnotics, anesthetics and analgesics on sleep architecture, the underlying mechanisms and the relevance to OSA. Indeed, these classes of drugs alter sleep architecture, which likely significantly contributes to abnormal postoperative sleep architecture, exacerbation of OSA and postoperative complications.

Sleep and physical activity measured by accelerometry in Crohn's disease

BACKGROUND

Sleep and physical activity are inherent to human living, yet appear affected by Crohn's disease (CD), resulting in fatigue and disability.

AIM

To objectively assess sleep quality and physical activity and their associations using accelerometers, comparing CD vs. matched healthy control (HC) subjects.

METHODS

Exactly 49 CD and 30 HC subjects completed surveys encompassing self-reported fatigue and sleep quality, pathology testing and wore an accelerometer for 7 days, measuring physical activity and sleep. In this cross-sectional observational study, per-group comparisons were performed and in CD, factors associated with reduced activity and/or sleep quality were assessed via multivariate analyses.

RESULTS

Regarding physical activity, CD subjects overall performed less total accelerometer counts (median 1.3 × 10(6) vs. 2.0 × 10(6) ), were more sedentary (97.7% vs. 96.2%) and completed fewer bouts of moderate-vigorous intensity exercise (1.0 vs. 5.0, each P < 0.01 (Mann-Whitney) than HC over 7 days. Factors associated with poor physical activity in CD included elevated serum CRP (OR = 22.6), lower vitamin D3 (OR = 13.1) and longer disease duration (OR = 1.2 per year, each P < 0.05). Regarding sleep, the CD group had similar total sleep time (median 458 vs. 447 min, P = 0.56), but more awakenings post-sleep onset (22 vs. 11, P = 0.01). Factors associated with severe sleep dysfunction in CD included lower haemoglobin (OR = 6.7) concurrent anti-TNF (OR = 6.5, each P < 0.05) and opioid therapy (OR = 6.6, P = 0.09).

CONCLUSION

Utilising objective measurement in a habitual context over 7 days, patients with Crohn's disease exhibited poorer sleep quality and less physical activity than well-matched healthy controls.

Sleep and fatigue in pediatric oncology: A review of the literature

Cancer in children has detrimental effects on sleep patterns and sleep quality, which in turn impacts on the perception of, and the ability to cope with, the emotional and physical challenges associated with both the disease and its treatment. This places an added burden on their quality of life that can last many years beyond diagnosis and treatment. In addition to the effect of the cancer itself, surgery, chemotherapy and radiotherapy can all contribute both short and long term to sleep disruption. Sleep disorders have also been associated with pain, fatigue, medication and hospitalisation in children suffering from cancer. This review will explore the relationship between childhood cancer and associated sleep disorders, in the acute stage of diagnosis, during treatment and in the years following. We will discuss the possible causes and the current treatment modalities used to treat sleep disorders in children with cancer, and in childhood cancer survivors. It has been estimated that the recent advances in treatment have improved the overall five year survival rate for all childhood cancers to over 80%, with some cancers achieving a near 100% cure rate such as early stage Wilms' tumour. Thus, recognition and appropriate treatment of associated sleep disorders is essential to optimise long term quality of life.

Fighting insomnia and battling lethargy: the yin and yang of palliative care

There is an interdependent relationship between insomnia and fatigue in the medical literature, but both remain distinct entities. Insomnia entails problematic sleep initiation, maintenance, or restoration with an accompanying decrease in perceived daytime function. Lethargy is a symptom that has a wide differential diagnosis that heavily overlaps with cancer-related fatigue; however, insomnia may contribute to worsened fatigue and lethargy in cancer patients. Insomnia is a major risk factor for mood disturbances such as depression, which may also contribute to lethargy in this at-risk population. The pathophysiology of fatigue and insomnia is discussed in this review, including their differential diagnoses as well as the emerging understanding of the roles of neurotransmitters, branched-chain amino acids, and inflammatory cytokines. Treatment approaches for insomnia and fatigue are also discussed and reviewed, including the role of hypnotics, psychotropics, hormonal agents, and alternative therapies.

Sleep in the Intensive Care Unit

Patients in the intensive care unit (ICU) are susceptible to sleep deprivation. Disrupted sleep is associated with increased morbidity and mortality in the critically ill patients. The etiology of sleep disruption is multifactorial. The article reviews the literature on sleep in the ICU, the effects of sleep deprivation, and strategies to promote sleep in the ICU. Until the impact of disrupted sleep is better explained, it is appropriate to provide critically ill patients with consolidated, restorative sleep.

Postoperative Changes in Sleep-disordered Breathing and Sleep Architecture in Patients with Obstructive Sleep Apnea

Background:

Anesthetics, analgesics, and surgery may profoundly affect sleep architecture and aggravate sleep-related breathing disturbances. The authors hypothesized that patients with preoperative polysomnographic evidence of obstructive sleep apnea (OSA) would experience greater changes in these parameters than patients without OSA.

Methods:

After obtaining approvals from the Institutional Review Boards, consented patients underwent portable polysomnography preoperatively and on postoperative nights (N) 1, 3, 5, and 7 at home or in hospital. The primary and secondary outcome measurements were polysomnographic parameters of sleep-disordered breathing and sleep architecture.

Results:

Of the 58 patients completed the study, 38 patients had OSA (apnea hypopnea index [AHI] &gt;5) with median preoperative AHI of 18 events per hour and 20 non-OSA patients had median preoperative AHI of 2. AHI was increased after surgery in both OSA and non-OSA patients (P &lt; 0.05), with peak increase on postoperative N3 (OSA vs. non-OSA, 29 [14, 57] vs. 8 [2, 18], median [25th, 75th percentile], P &lt; 0.05). Hypopnea index accounted for 72% of the postoperative increase in AHI. The central apnea index was low (median = 0) but was significantly increased on postoperative N1 in only non-OSA patients. Sleep efficiency, rapid eye movement sleep, and slow-wave sleep were decreased on N1 in both groups, with gradual recovery.

Conclusions:

Postoperatively, sleep architecture was disturbed and AHI was increased in both OSA and non-OSA patients. Although the disturbances in sleep architecture were greatest on postoperative N1, breathing disturbances during sleep were greatest on postoperative N3.

Factors Associated with Postoperative Exacerbation of Sleep-disordered Breathing

Introduction:

The knowledge on the mechanism of the postoperative exacerbation of sleep-disordered breathing may direct the perioperative management of patients with obstructive sleep apnea. The objective of this study is to investigate the factors associated with postoperative severity of sleep-disordered breathing.

Methods:

After obtaining approvals from Institutional Review Boards, consenting patients underwent portable polysomnography preoperatively, and on postoperative nights 1 and 3 in hospital or at home. The primary outcomes were polysomnography parameters measuring the sleep-disordered breathing. They were treated as repeated measurement variables and analyzed for associated factors by mixed models.

Results:

Three hundred seventy-six patients, 168 men and 208 women, completed polysomnography on preoperative and postoperative night 1. Age was 59 ± 12 yr (mean ± SD). Preoperative apnea–hypopnea index (AHI) was 12 (4, 26) (median [25th, 75th percentile]) events per hour. Thirty-five patients had minor surgeries, 292 intermediate surgeries, and 49 major surgeries, with 210 general anesthesia and 166 regional anesthesia. The 72-h opioid dose was 55 (14, 85) mg intravenous morphine-equivalent dose. Preoperative AHI, age, and 72-h opioid dose were associated with postoperative AHI. Preoperative central apnea index, male sex, and general anesthesia were associated with postoperative central apnea index. Slow wave sleep percentage was inversely associated with postoperative AHI and central apnea index.

Conclusions:

Patients with a higher preoperative AHI were predicted to have a higher postoperative AHI. Preoperative AHI, age, and 72-h opioid dose were positively associated with postoperative AHI. Preoperative central apnea, male sex, and general anesthesia were associated with postoperative central apnea index.

Amygdala opioid receptors mediate the electroacupuncture-induced deterioration of sleep disruptions in epilepsy rats

BACKGROUND

Clinical and experimental evidence demonstrates that sleep and epilepsy reciprocally affect each other. Previous studies indicated that epilepsy alters sleep homeostasis; in contrast, sleep disturbance deteriorates epilepsy. If a therapy possesses both epilepsy suppression and sleep improvement, it would be the priority choice for seizure control. Effects of acupuncture of Feng-Chi (GB20) acupoints on epilepsy suppression and insomnia treatment have been documented in the ancient Chinese literature, Lingshu Jing (Classic of the Miraculous Pivot). Therefore, this study was designed to investigate the effect of electroacupuncture (EA) stimulation of bilateral Feng-Chi acupoints on sleep disruptions in rats with focal epilepsy.

RESULTS

Our result indicates that administration of pilocarpine into the left central nucleus of amygdala (CeA) induced focal epilepsy and decreased both rapid eye movement (REM) sleep and non-REM (NREM) sleep. High-frequency (100 Hz) EA stimulation of bilateral Feng-Chi acupoints, in which a 30-min EA stimulation was performed before the dark period of the light:dark cycle in three consecutive days, further deteriorated pilocarpine-induced sleep disruptions. The EA-induced exacerbation of sleep disruption was blocked by microinjection of naloxone, μ- (naloxonazine), κ- (nor-binaltorphimine) or δ-receptor antagonists (natrindole) into the CeA, suggesting the involvement of amygdaloid opioid receptors.

CONCLUSION

The present study suggests that high-frequency (100 Hz) EA stimulation of bilateral Feng-Chi acupoints exhibits no benefit in improving pilocarpine-induced sleep disruptions; in contrast, EA further deteriorated sleep disturbances. Opioid receptors in the CeA mediated EA-induced exacerbation of sleep disruptions in epileptic rats.

Sleep quality in heroin addicts under methadone maintenance treatment

Hsu W-Y, Chiu N-Y, Liu J-T, Wang C-H, Chang T-G, Liao Y-C, Kuo P-I. Sleep quality in heroin addicts under methadone maintenance treatment.

Background: Sleep disturbance is a common phenomenon among opiate addicts. The side effects of opiate addiction or opiate withdrawal might result in sleep disturbance. However, their problems might be related to sedative medication abuse, alcohol abuse or heroin relapse. Sleep is an important issue in this population.

Objective: To evaluate the prevalence of sleep disorders in heroin addicts receiving methadone maintenance treatment (MMT) and analyse the correlation between related factors, such as age at opiate exposure, opiate exposure duration, duration in MMT, methadone current dosage, methadone attendance rate and the severity of sleep disorders.

Method: We enrolled 121 heroin addicts who were receiving MMT. We collected data on the duration of insomnia, hypnotic history, Visual Analogue Scale-10 of sleep quality, Pittsburgh Sleep Quality Index (PSQI), methadone dosage, methadone history and opiate history.

Results: The mean of the PSQI was 9.1 ± 5.4, and 70.2% of patients had PSQI scores >5, indicating they were poor sleepers. We also found the PSQI scores were correlated significantly with the methadone dosage.

Conclusions: The sleep disturbance prevalence rate of opiate addicts under MMT was high in Taiwan, as shown in the previous studies, and the severity of sleep disturbance has been underestimated.

Sedation and sleep disturbances in the ICU

Sedation in the ICU is, paradoxically, both a cause and a potential treatment for the sleep disruption almost universally observed in the critically ill. A patient-focused sedation strategy that minimizes unnecessary medication, avoids medication withdrawal, addresses the specific impediments to sleep, and serves as an adjunct to attentive environmental control may ultimately serve patients best.

Buprenorphine disrupts sleep and decreases adenosine concentrations in sleep-regulating brain regions of Sprague Dawley rat

BACKGROUND

Buprenorphine, a partial μ-opioid receptor agonist and κ-opioid receptor antagonist, is an effective analgesic. The effects of buprenorphine on sleep have not been well characterized. This study tested the hypothesis that an antinociceptive dose of buprenorphine decreases sleep and decreases adenosine concentrations in regions of the basal forebrain and pontine brainstem that regulate sleep.

METHODS

Male Sprague Dawley rats were implanted with intravenous catheters and electrodes for recording states of wakefulness and sleep. Buprenorphine (1 mg/kg) was administered systemically via an indwelling catheter and sleep-wake states were recorded for 24 h. In additional rats, buprenorphine was delivered by microdialysis to the pontine reticular formation and substantia innominata of the basal forebrain while adenosine was simultaneously measured.

RESULTS

An antinociceptive dose of buprenorphine caused a significant increase in wakefulness (25.2%) and a decrease in nonrapid eye movement sleep (-22.1%) and rapid eye movement sleep (-3.1%). Buprenorphine also increased electroencephalographic delta power during nonrapid eye movement sleep. Coadministration of the sedative-hypnotic eszopiclone diminished the buprenorphine-induced decrease in sleep. Dialysis delivery of buprenorphine significantly decreased adenosine concentrations in the pontine reticular formation (-14.6%) and substantia innominata (-36.7%). Intravenous administration of buprenorphine significantly decreased (-20%) adenosine in the substantia innominata.

CONCLUSIONS

Buprenorphine significantly increased time spent awake, decreased nonrapid eye movement sleep, and increased latency to sleep onset. These disruptions in sleep architecture were mitigated by coadministration of the nonbenzodiazepine sedative-hypnotic eszopiclone. The buprenorphine-induced decrease in adenosine concentrations in basal forebrain and pontine reticular formation is consistent with the interpretation that decreasing adenosine in sleep-regulating brain regions is one mechanism by which opioids disrupt sleep.

Neuropsychiatric adverse effects of centrally acting antiobesity drugs

INTRODUCTION

Central neurochemical systems including the monoamine, opioid, and cannabinoid systems have been promising targets for antiobesity drugs that modify behavioral components of obesity. In addition to modulating eating behavior, centrally acting antiobesity drugs are also likely to alter emotional behavior and cognitive function due to the high expression of receptors for the neurochemical systems targeted by these drugs within the fronto-striatal and limbic circuitry.

METHODS

This paper reviewed the neuropsychiatric adverse effects of past and current antiobesity drugs, with a central mechanism of action, linking the adverse effects to their underlying neural substrates and neurochemistry.

RESULTS

Antiobesity drugs were found to have varying neuropsychiatric adverse event profiles. Insomnia was the most common adverse effect with drugs targeting monoamine systems (sibutramine, bupropion and tesofensine). These drugs had some positive effects on mood and anxiety and may have added therapeutic benefits in obese patients with comorbid depression and anxiety symptoms. Sedation and tiredness were the most common adverse effects reported with drugs targeting the m-opioid receptors (i.e., naltrexone) and combination therapies targeting the opioid and monoamine systems (i.e., Contrave™). Cognitive impairments were most frequently associated with the antiepileptic drugs, topiramate and zonisamide, consistent with their sedative properties. Drugs targeting the cannabinoid system (rimonabant and taranabant) were consistently associated with symptoms of anxiety and depression, including reports of suicidal ideation. Similar adverse events have also been noted for the D₁/D₅ antagonist ecopipam.

CONCLUSION

These findings highlight the need to assess neuropsychiatric adverse events comprehensively using sensitive and validated methods early in the clinical development of candidate antiobesity drugs with a central mechanism of action.

Opioid-induced decreases in rat brain adenosine levels are reversed by inhibiting adenosine deaminase

BACKGROUND

Opioids disrupt sleep and adenosine promotes sleep, but no studies have characterized the effects of opioids on adenosine levels in brain regions known to regulate states of arousal. Delivering opioids to the pontine reticular formation (PRF) and substantia innominata (SI) region of the basal forebrain disrupts sleep. In contrast, administering adenosine agonists to the PRF or SI increases sleep. These findings encouraged the current study testing the hypothesis that microdialysis delivery of opioids to the PRF or SI decreases adenosine levels in the PRF or SI, respectively.

METHODS

A microdialysis probe was placed in the PRF of isoflurane anesthetized rats and perfused with Ringer's solution (control) followed by Ringer's solution containing morphine (0, 10, 30, 100, or 300 microm), fentanyl (100 microm), morphine (100 microm) and the adenosine deaminase inhibitor EHNA (100 microm), or naloxone (10 microm) and morphine (100 microm). Additional experiments measured adenosine levels in the SI before and during microdialysis delivery of morphine, fentanyl, and morphine plus EHNA.

RESULTS

Morphine caused a significant (P < 0.05) concentration-dependent decrease in PRF adenosine levels. The significant decrease (-20%) in adenosine caused by 100 microm morphine was blocked by coadministration of naloxone. Fentanyl also significantly decreased (-13.3%) PRF adenosine. SI adenosine levels were decreased by morphine (-26.8%) and fentanyl (-27.4%). In both PRF and SI, coadministration of morphine and EHNA prevented the significant decrease in adenosine levels caused by morphine alone.

CONCLUSIONS

These data support the interpretation that decreased adenosine levels in sleep-regulating brain regions may be one of the mechanisms by which opioids disrupt sleep.

Sedation and sleep disturbances in the ICU

The need for compassionate care of the critically ill often compels clinicians to treat these patients with pharmacologic sedation. Although patients may appear to be asleep under the influence of these sedating medications, the relationship between sleep and sedation is complex and not fully understood. These medications exert their effects at different points along the central nervous system's natural sleep pathway, leading to similarities and differences between the two states. This relationship is important because critically ill patients sleep poorly and this phenomenon has been linked to poor intensive care unit outcomes. Therefore, greater awareness of the effects of these medications on sleep may lead to sedation protocols that further improve outcomes. This article reviews the relationship between sedation and sleep from physiologic and clinical perspectives.

Pharmacology I: effects on sleep of commonly used ICU medications. Crit Care Clin. 2008;24:477-491, vi. [PMID: 18538196 DOI: 10.1016/j.ccc.2008.02.008]

Critically ill patients are almost universally administered medications to treat their acute illnesses and to maximize their comfort. The effects of many of these medications on their sleep, however, may be important. It is known that critically ill patients have severely disrupted sleep and that this disrupted sleep has a negative impact on ICU outcomes. This article reviews how some commonly used ICU medications may affect patients' sleep.

Delirium and use of sedation agents in intensive care

AIM

The aim of the review was to consider the relationship between delirium and aspects of sedative and analgesic drug use in mechanically ventilated intensive care patients. The basis for routine delirium screening and the implications for nurses are discussed along with a brief outline of the treatment of delirium.

BACKGROUND AND CONTEXT

Delirium is common in intensive care patients and like other markers of organ failure is associated with worse outcomes. The risk of developing delirium is dependent on the patients' individual vulnerability and on the burden of precipitating factors they are exposed to. Detection of delirium in intensive care patients is often difficult and requires the regular use of a validated screening tool. Intensive care patients are exposed to multiple delirium risk factors, and sedative and analgesic agents present an important subgroup, which we can attempt to control. Sedative and analgesic drug choice, their mode of administration, monitoring and titration have consequences for delirium development.

METHOD

Literature review.

CONCLUSIONS

Sedative and analgesic drugs have an important role in the prevention and treatment of delirium in intensive care patients. Routine delirium screening should be included as part of sedation monitoring practice. When detected, treatment is focused on the prompt correction of precipitating factors, non-pharmacological interventions and appropriate drug therapy for symptom control.

Opioids, sleep architecture and sleep-disordered breathing

Opioid use whether acute or chronic, illicit or therapeutic is prevalent in Western societies. Opioid receptors are located in the same nuclei that are active in sleep regulation and opioid peptides are suggested to be involved in the induction and maintenance of the sleep state. mu-Opioids are the most commonly used opioids and are recognized respiratory depressants that cause abnormal awake ventilatory responses to hypercapnia and hypoxia. Abnormal sleep architecture has been reported during the process of opioids induction, maintenance and withdrawal. During induction and maintenance of opioid use there is reduction of rapid eye movement (REM) sleep and slow wave sleep. More recently, central sleep apnoea (CSA) has been reported with chronic opioid use and 30% of stable methadone maintenance treatment patients have CSA. Given these facts, it is sobering to note the paucity of human data available regarding the effects of short and long-term opioid use on sleep architecture and respiration during sleep. In this manuscript, we review the current knowledge regarding the effects of mu-opioids on sleep and respiration during sleep and suggest research pathways to advance our knowledge and to explore the possible responsible mechanisms related to these effects.

Sleep and GABA levels in the oral part of rat pontine reticular formation are decreased by local and systemic administration of morphine

Morphine, a mu-opioid receptor agonist, is a commonly prescribed treatment for pain. Although highly efficacious, morphine has many unwanted side effects including disruption of sleep and obtundation of wakefulness. One mechanism by which morphine alters sleep and wakefulness may be by modulating GABAergic signaling in brain regions regulating arousal, including the pontine reticular nucleus, oral part (PnO). This study used in vivo microdialysis in unanesthetized Sprague-Dawley rat to test the hypothesis that mu-opioid receptors modulate PnO GABA levels. Validation of the high performance liquid chromatographic technique used to quantify GABA was obtained by dialyzing the PnO (n=4 rats) with the GABA reuptake inhibitor nipecotic acid (500 microM). Nipecotic acid caused a 185+/-20% increase in PnO GABA levels, confirming chromatographic detection of GABA and demonstrating the existence of functional GABA transporters in rat PnO. Morphine caused a concentration-dependent decrease in PnO GABA levels (n=25 rats). Coadministration of morphine (100 microM) with naloxone (1 microM), a mu-opioid receptor antagonist, blocked the morphine-induced decrease in PnO GABA levels (n=5 rats). These results show for the first time that mu-opioid receptors in rat PnO modulate GABA levels. A second group of rats (n=6) was used to test the hypothesis that systemically administered morphine also decreases PnO GABA levels. I.v. morphine caused a significant (P<0.05) decrease (19%) in PnO GABA levels relative to control i.v. infusions of saline. Finally, microinjections followed by 2 h recordings of electroencephalogram and electromyogram tested the hypothesis that PnO morphine administration disrupts sleep (n=8 rats). Morphine significantly (P<0.05) increased the percent of time spent in wakefulness (65%) and significantly (P<0.05) decreased the percent of rapid eye movement (REM) sleep (-53%) and non-REM sleep (-69%). The neurochemical and behavioral data suggest that morphine may disrupt sleep, at least in part, by decreasing GABAergic transmission in the PnO.

Beta-endorphin modulates the acute response to a social conflict in male mice but does not play a role in stress-induced changes in sleep

Beta-endorphin is an endogenous opioid peptide that is released during stress and has been associated with many physiological functions. In this experiment beta-endorphin deficient mice were used to study the role of endorphins in the acute physiological and behavioral responses to a social conflict, as well as their role in social stress-induced changes in sleep. Adult male beta-endorphin deficient and wild type mice were subjected to the stress of a 1 h social conflict with an aggressive dominant conspecific. After the conflict, the beta-endorphin deficient mice had higher corticosterone levels but the peak increase in body temperature was not different from that in wild type animals. In fact, body temperature returned to baseline levels faster in the beta-endorphin deficient mice. During their interaction with the aggressive conspecific several of the beta-endorphin deficient mice showed clear signs of counter aggression whereas this was not seen in any of the wild type mice. Overall, the beta-endorphin deficient mice and wild type mice had fairly similar sleep patterns under baseline conditions and also showed similar amounts of NREM sleep, REM sleep and EEG slow-wave energy after the social conflict. In addition, no differences were found in the sleep patterns of mice that showed counter aggression and mice that did not. In conclusion, the results suggest that beta-endorphin modulates the acute endocrine, thermoregulatory and behavioral response to a social conflict but the data do not support a major role for beta-endorphin in the regulation of sleep or social stress-induced alterations in sleep.

Opioids, sleep, and cancer-related fatigue

Oddly enough, little is known about the effects on sleep of commonly administered analgesic medications. Even less is known about their effect on next-day fatigue, mood, and cognitive functioning. We speculate that part of the fatigue typically experienced by cancer patients can be attributed to disruption of sleep by opioid medications they are taking. Fatigue and sleep are critical to the quality of life of cancer patients. Research is needed to assess the sleep and next-day consequences that can be expected from typical doses of different types of pain medications.

Definition of and mechanism for opioid-induced sedation

Although sedation is acknowledged to be one of the most common side effects of opioid analgesics, the mechanisms and characteristics of this phenomenon remain elusive, and research in this area is extremely limited. This report integrates research findings on the mechanism of action of opioids with research findings on the phenomenon of consciousness to develop a model of how opioids may act in the central nervous system to produce sedation. Based on this integration, a definition of opioid-induced sedation is proposed to encourage dialogue and research on this perplexing and clinically significant phenomenon.

Association of airway obstruction, sleep, and phasic abdominal muscle activity after upper abdominal surgery

We recorded nasal gas flow, sleep stage, and abdominal muscle EMG pattern in 11 patients throughout the night after abdominal surgery, to examine the association between phasic activity of the abdominal muscles, sleep stage, and flow disturbance. We used a miniaturized data logging system, and obtained satisfactory records in eight patients. The data were divided into 30-s epochs. Each epoch was classified as either awake or asleep. The epochs were also classified for the presence of phasic activity in the external oblique abdominal muscle, and for evidence of airway obstruction. Association between these features was tested by a quasi likelihood log linear model. Values given are median (quartiles) for the eight subjects. Sleep occurred for 62 (46-69)% of the study time. During sleep, inspiratory flow was normal for 69 (48-81)% of the time, whereas during wakefulness, the flow pattern was normal for 51 (28-77)% of the time. Phasic activity was present 16 (12-25)% of the time during sleep and 24 (19-37)% of the time during wakefulness (P<0.001). In the awake state, when breathing was normal, phasic activity was present 16 (11-30)% of the time. When breathing was obstructed, phasic activity was present 38 (25-44)% of the time (P<0.001). These surprising findings suggest that sleep may be seriously disturbed by airway obstruction, so that a stable sleep state is not reached. We could not confirm previous findings that disturbed breathing in post-operative patients only occurs during sleep.

Infant stress and sleep deprivation as an aetiological basis for the sudden infant death syndrome

SIDS is almost invariably sleep-related. Viable syndrome aetiology must be compatible with its many epidemiologically diverse risk factors, each of which directly or indirectly associates with the creation of psychological and/or physiological infant stress, and the subsequent disruption of normal, contented sleep. During essential deep 'rebound' recovery sleep, arousal ability and upper airway muscle tone decrease further to that in normal sleep, with subsequent upper airway obstruction. When stress impact causes sufficient sleep disruption and physiological fatigue, a failure to arouse and so restore sufficient tone to overcome such obstruction results in sudden, unexpected death. SIDS has therefore many causes which share a final lethal mechanical pathway. Evidence is presented for obstructive apnoea during sleep as being the primary syndrome death mode, for sleep disruption, reduced arousal ability, and infant stress in SIDS, and for risk factor association with the creation of this stress. Specific infant vulnerability in the first 6 months of life to stress predominantly related to total dependency on a carer for gratification of need, and to obstructive sleep apnoea due to normal anatomical, physical, and respiratory immaturity, including rapid physiological fatigue, and peaks in sleep and thermal stress vulnerability, are discussed. Further reasons for the limited age period of SIDS, and for reduced neonatal risk, are given. Prone sleeping risk can relate to positional airway obstruction during normal sleep without prior infant stress. Much of SIDS aetiology appears to concern factors related to socio-economic deprivation and subsequent sub-optimal infant care.