Reversal of the sleep-wake cycle by heroin self-administration in rats

Oral Fentanyl Consumption and Withdrawal Impairs Fear Extinction Learning and Enhances Basolateral Amygdala Principal Neuron Excitatory-Inhibitory Balance in Male and Female Mice

The number of opioid overdose deaths has increased over the past several years, mainly driven by an increase in the availability of highly potent synthetic opioids, like fentanyl, in the un-regulated drug supply. Over the last few years, changes in the drug supply, and in particular the availability of counterfeit pills containing fentanyl, have made oral use of opioids a more common route of administration. Here, we used a drinking in the dark (DiD) paradigm to model oral fentanyl self-administration using increasing fentanyl concentrations in male and female mice over 5 weeks. Fentanyl consumption peaked in both female and male mice at the 30 µg/mL dose, with female mice consuming significantly more fentanyl than male mice. Mice consumed sufficient fentanyl such that withdrawal was precipitated with naloxone, with males having more withdrawal symptoms, despite lower pharmacological exposure. We also performed behavioral assays to measure avoidance behavior and reward-seeking during fentanyl abstinence. Female mice displayed reduced avoidance behaviors in the open field assay, whereas male mice showed increased avoidance in the light/dark box assay. Female mice also exhibited increased reward-seeking in the sucrose preference test. Fentanyl-consuming mice of both sexes showed impaired cued fear extinction learning following fear conditioning and increased excitatory synaptic drive and increased excitability of BLA principal neurons. Our experiments demonstrate that long-term oral fentanyl consumption results in wide-ranging physiological and behavioral disruptions. This model could be useful to further study fentanyl withdrawal syndrome and behaviors and neuroplasticity associated with protracted fentanyl withdrawal.

Probing different paradigms of morphine withdrawal on sleep behavior in male and female C57BL/6J mice

Opioid misuse has dramatically increased over the last few decades resulting in many people suffering from opioid use disorder (OUD). The prevalence of opioid overdose has been driven by the development of new synthetic opioids, increased availability of prescription opioids, and more recently, the COVID-19 pandemic. Coinciding with increases in exposure to opioids, the United States has also observed increases in multiple Narcan (naloxone) administrations as a life-saving measures for respiratory depression, and, thus, consequently, naloxone-precipitated withdrawal. Sleep dysregulation is a main symptom of OUD and opioid withdrawal syndrome, and therefore, should be a key facet of animal models of OUD. Here we examine the effect of precipitated and spontaneous morphine withdrawal on sleep behaviors in C57BL/6 J mice. We find that morphine administration and withdrawal dysregulate sleep, but not equally across morphine exposure paradigms. Furthermore, many environmental triggers promote relapse to drug-seeking/taking behavior, and the stress of disrupted sleep may fall into that category. We find that sleep deprivation dysregulates sleep in mice that had previous opioid withdrawal experience. Our data suggest that the 3-day precipitated withdrawal paradigm has the most profound effects on opioid-induced sleep dysregulation and further validates the construct of this model for opioid dependence and OUD.

Probing different paradigms of morphine withdrawal on sleep behavior in male and female C57BL/6J mice

Opioid misuse has dramatically increased over the last few decades resulting in many people suffering from opioid use disorder (OUD). The prevalence of opioid overdose has been driven by the development of new synthetic opioids, increased availability of prescription opioids, and more recently, the COVID-19 pandemic. Coinciding with increases in exposure to opioids, the United States has also observed increases in multiple Narcan (naloxone) administrations as life-saving measures for respiratory depression, and, thus, consequently, naloxone-precipitated withdrawal. Sleep dysregulation is a main symptom of OUD and opioid withdrawal syndrome, and therefore, should be a key facet of animal models of OUD. Here we examine the effect of precipitated and spontaneous morphine withdrawal on sleep behaviors in C57BL/6J mice. We find that morphine administration and withdrawal dysregulate sleep, but not equally across morphine exposure paradigms. Furthermore, many environmental triggers promote relapse to drug-seeking/taking behavior, and the stress of disrupted sleep may fall into that category. We find that sleep deprivation dysregulates sleep in mice that had previous opioid withdrawal experience. Our data suggest that the 3-day precipitated withdrawal paradigm has the most profound effects on opioid-induced sleep dysregulation and further validates the construct of this model for opioid dependence and OUD.

Highlights

Morphine withdrawal differentially dysregulates the sleep of male and female mice3-day precipitated withdrawal results in larger changes than spontaneous withdrawalOpioid withdrawal affects responses to future sleep deprivation differently between sexes.

Metabotropic glutamate receptor function and regulation of sleep-wake cycles

Metabotropic glutamate (mGlu) receptors are the most abundant family of G-protein coupled receptors and are widely expressed throughout the central nervous system (CNS). Alterations in glutamate homeostasis, including dysregulations in mGlu receptor function, have been indicated as key contributors to multiple CNS disorders. Fluctuations in mGlu receptor expression and function also occur across diurnal sleep-wake cycles. Sleep disturbances including insomnia are frequently comorbid with neuropsychiatric, neurodevelopmental, and neurodegenerative conditions. These often precede behavioral symptoms and/or correlate with symptom severity and relapse. Chronic sleep disturbances may also be a consequence of primary symptom progression and can exacerbate neurodegeneration in disorders including Alzheimer's disease (AD). Thus, there is a bidirectional relationship between sleep disturbances and CNS disorders; disrupted sleep may serve as both a cause and a consequence of the disorder. Importantly, comorbid sleep disturbances are rarely a direct target of primary pharmacological treatments for neuropsychiatric disorders even though improving sleep can positively impact other symptom clusters. This chapter details known roles of mGlu receptor subtypes in both sleep-wake regulation and CNS disorders focusing on schizophrenia, major depressive disorder, post-traumatic stress disorder, AD, and substance use disorder (cocaine and opioid). In this chapter, preclinical electrophysiological, genetic, and pharmacological studies are described, and, when possible, human genetic, imaging, and post-mortem studies are also discussed. In addition to reviewing the important relationships between sleep, mGlu receptors, and CNS disorders, this chapter highlights the development of selective mGlu receptor ligands that hold promise for improving both primary symptoms and sleep disturbances.

Sleep is increased by liraglutide, a glucagon-like peptide-1 receptor agonist, in rats

INTRODUCTION

Sleep disturbances are prominent in drug use disorders, including those involving opioids in both humans and animals. Recent studies have shown that administration of liraglutide, a glucagon-like peptide-1 agonist, significantly reduces heroin taking and seeking in rats. In an effort to further understand the action of this substance on physiological functions and to evaluate safety issues for its potential clinical use, the aim of the present study was to determine whether the dose of liraglutide found effective in reducing responding for an opioid also could improve sleep in drug-naïve rats.

METHODS

Using a within-subjects design, adult male rats chronically implanted with EEG and EMG electrodes received subcutaneous injection of saline or 0.06, 0.10, 0.30 or 0.60 mg/kg liraglutide. The 0.10 and 0.30 mg/kg doses are known to be most effective in reducing responding for heroin in rats at light or dark onset during a 12:12 h light-dark cycle (0.10 mg/kg for taking and seeking, 0.30 mg/kg for seeking). EEG and EMG were recorded across the 24 h period following each injection.

RESULTS

After both dark and light onset injections, liraglutide dose-dependently decreased wakefulness and increased non-rapid eye movement (NREM) sleep except at the lowest dose. The bout length of wakefulness and NREM sleep were decreased and increased, respectively. Whether administered at light or dark onset, the above alterations occurred primarily during the dark period (i.e., during the active period). The animals' body weight was decreased after liraglutide treatments as expected since it is clinically used for the treatment of obesity.

CONCLUSION

These data indicate that liraglutide, at doses known to reduce responding for heroin and fentanyl, also increases NREM sleep, suggesting that the increase in sleep may contribute to the protective effects of liraglutide and may promote overall general health.

Sleep restriction during opioid abstinence affects the hypothalamic-pituitary-adrenal (HPA) axis in male and female rats

Hypothalamic-pituitary-adrenal (HPA) axis dynamics are disrupted by opioids and may be involved in substance abuse; this persists during withdrawal and abstinence and is associated with co-morbid sleep disruption leading to vulnerability to relapse. We hypothesized that chronic sleep restriction (SR) alters the HPA axis diurnal rhythm and the sexually dimorphic response to acute stressor during opioid abstinence. We developed a rat model to evaluate the effect of persistent sleep loss during opioid abstinence on HPA axis dynamics in male and female rats. Plasma ACTH and corticosterone were measured diurnally and in response to acute restraint stress in rats Before (control) compared to During subsequent opioid abstinence without or with SR. Abstinence, regardless of sleep state, led to an increase in plasma ACTH and corticosterone in the morning in males. There was a tendency for higher PM plasma ACTH during abstinence in SR males (p = 0.076). ACTH and corticosterone responses to restraint were reduced in male SR rats whereas there was a failure to achieve the post-restraint nadir in female SR rats. There was no effect of the treatments or interventions on adrenal weight normalized to body weight. SR resulted in a dramatic increase in hypothalamic PVN AVP mRNA and plasma copeptin in male but not female rats. This corresponded to the attenuation of the HPA axis stress response in SR males during opioid abstinence. We have identified a potentially unique, sexually dimorphic role for magnocellular vasopressin in the control of the HPA axis during opioid abstinence and sleep restriction.

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.

Chronic Sleep Deprivation Blocks Voluntary Morphine Consumption but Not Conditioned Place Preference in Mice

The opioid epidemic remains a significant healthcare problem and is attributable to over 100,000 deaths per year. Poor sleep increases sensitivity to pain, impulsivity, inattention, and negative affect, all of which might perpetuate drug use. Opioid users have disrupted sleep during drug use and withdrawal and report poor sleep as a reason for relapse. However, preclinical studies investigating the relationship between sleep loss and substance use and the associated underlying neurobiological mechanisms of potential interactions are lacking. One of the most common forms of sleep loss in modern society is chronic short sleep (CSS) (<7 h/nightly for adults). Here, we used an established model of CSS to investigate the influence of disrupted sleep on opioid reward in male mice. The CSS paradigm did not increase corticosterone levels or depressive-like behavior after a single sleep deprivation session but did increase expression of Iba1, which typically reflects microglial activation, in the hypothalamus after 4 weeks of CSS. Rested control mice developed a morphine preference in a 2-bottle choice test, while mice exposed to CSS did not develop a morphine preference. Both groups demonstrated morphine conditioned place preference (mCPP), but there were no differences in conditioned preference between rested and CSS mice. Taken together, our results show that recovery sleep after chronic sleep disruption lessens voluntary opioid intake, without impacting conditioned reward associated with morphine.

Worsening sleep quality across the lifespan and persistent sleep disturbances in persons with opioid use disorder

STUDY OBJECTIVES

Individuals with opioid use disorder (OUD) may experience worsening sleep quality over time, and a subset of individuals may have sleep disturbances that precede opioid use and do not resolve following abstinence. The purpose of the present study was to (1) collect retrospective reports of sleep across the lifespan and (2) identify characteristics associated with persistent sleep disturbance and changes in sleep quality in persons with OUD.

METHODS

Adults with OUD (n = 154) completed a cross-sectional study assessing current and past sleep disturbance, opioid use history, and chronic pain. Repeated-measures analysis of variance was used to examine changes in retrospectively reported sleep quality, and whether changes varied by screening positive for insomnia and/or chronic pain. Multivariate linear regression analyses were used to identify additional correlates of persistent sleep disturbance.

RESULTS

Participants reported that their sleep quality declined over their lifespan. Changes in reported sleep over time varied based on whether the individual screened positive for co-occurring insomnia and/or chronic pain. In regression analyses, female sex (β = 0.16, P = .042), a greater number of treatment episodes (β = 0.20, P = .024), and positive screens for chronic pain (β = 0.19, P = .018) and insomnia (β=0.22, P = .013) were associated with self-reported persistent sleep disturbance. Only a portion of participants who screened positive for sleep disorders had received a formal diagnosis.

CONCLUSIONS

OUD treatment providers should routinely screen for co-occurring sleep disturbance and chronic pain. Interventions that treat co-occurring OUD, sleep disturbance, and chronic pain are needed.

CITATION

Ellis JD, Mayo JL, Gamaldo CE, Finan PH, Huhn AS. Worsening sleep quality across the lifespan and persistent sleep disturbances in persons with opioid use disorder. J Clin Sleep Med. 2022;18(2):587-595.

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.

Sleeping Patterns in Patients with Opioid Use Disorder: Effects of Opioid Maintenance Treatment and Detoxification

The aim of the study was to explore whether abstinent patients on recent opioid detoxification or on opioid maintenance treatment suffer from sleeping problems. 199 patients on opioid maintenance treatment (methadone, diacetylmorphine and buprenorphine) or recent opioid detoxification were included in this exploratory cross-sectional study. We used the Pittsburgh Sleep Quality Index (PSQI) and the Regensburger Insomnia Scale (RIS) in order to assess potential sleeping problems. There was a significant effect of the condition "opioid maintenance" or "recent opioid detoxification" on the total score of PSQI and RIS. All opioid maintenance drugs used by the study population were associated with more sleeping problems compared to the detoxification group when calculated with RIS values. Recently abstinent patients (opioid detoxification) displayed significantly fewer sleep disturbances than opioid-maintained patients. Since sleeping problems can seriously impair treatment success and quality of life, screening for sleep disturbances and their subsequent treatment is of pronounced relevance.

Direct activation of G-protein-gated inward rectifying K+ channels promotes nonrapid eye movement sleep

STUDY OBJECTIVES

A major challenge in treating insomnia is to find effective medicines with fewer side effects. Activation of G-protein-gated inward rectifying K+ channels (GIRKs) by GABAB agonists baclofen or γ-hydroxybutyric acid (GHB) promotes nonrapid eye movement (NREM) sleep and consolidates sleep. However, baclofen has poor brain penetration, GHB possesses abuse liability, and in rodents both drugs cause spike-wave discharges (SWDs), an absence seizure activity. We tested the hypothesis that direct GIRK activation promotes sleep without inducing SWD using ML297, a potent and selective GIRK activator.

METHODS

Whole-cell patch-clamp recordings from hypocretin/orexin or hippocampal neurons in mouse brain slices were made to study neuronal excitability and synaptic activity; spontaneous activity, locomotion, contextual and tone-conditioned memory, and novel object recognition were assessed. Electroencephalogram/electromyogram (EEG/EMG) recordings were used to study GIRK modulation of sleep.

RESULTS

ML297, like baclofen, caused membrane hyperpolarization, decreased input resistance, and blockade of spontaneous action potentials. Unlike baclofen, ML297 (5-10 µM) did not cause significant depression of postsynaptic excitatory and inhibitory currents (EPSCs-IPSCs), indicating preferential postsynaptic inhibition. ML297 (30 mg/kg, i.p.) inhibited wake activity and locomotion, and preferentially increased NREM sleep without altering EEG delta power, REM sleep, inducing SWDs, or impairing conditioned memory and novel object recognition.

CONCLUSIONS

This study finds that direct activation of neuronal GIRK channels modulates postsynaptic membrane excitability and prolongs NREM sleep without changing sleep intensity, inducing SWDs, or impairing memory in rodents. These results suggest that direct GIRK activation with a selective compound may present an innovative approach for the treatment of chronic insomnia.

Morphine-Induced Dendritic Spine Remodeling in Rat Nucleus Accumbens Is Corticosterone Dependent

BACKGROUND

Chronic morphine treatments produce important morphological changes in multiple brain areas including the nucleus accumbens.

METHODS

In this study, we have investigated the effect of chronic morphine treatment at a relatively low dose on the morphology of medium spiny neurons in the core and shell of the nucleus accumbens in rats 1 day after the last injection of a chronic morphine treatment (5 mg/kg once per day for 14 days). Medium spiny neurons were labeled with 1,1' dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate crystal and analyzed by confocal laser-scanning microscope.

RESULTS

Our results show an increase of thin spines and a decrease of stubby spines specifically in the shell of morphine-treated rats compared with control. Since morphine-treated rats also presented an elevation of corticosterone level in plasma, we explored whether spine alterations induced by morphine treatment in the nucleus accumbens could be affected by the depletion of the hormone. Thus, bilaterally adrenalectomized rats were treated with morphine in the same conditions. No more alteration in stubby spines in the shell was detected in morphine-treated rats with a depletion of corticosterone, while a significant increase was observed in mushroom spines in the shell and stubby spines in the core. Regarding the thin spines, the increase observed with morphine compared with saline was lower in adrenalectomized rats than in nonadrenalectomized animals.

CONCLUSION

These results indicate that dendritic spine remodeling in nucleus accumbens following chronic morphine treatment at relatively low doses is dependent on corticosterone levels.

Heroin self-administration as a function of time of day in rats

RATIONALE

Drug addiction is a complex disease that is impacted by numerous factors. One such factor, time of day, influences drug intake, but there have been no investigations of how time of day affects the amount of drug taken and the development of addiction-like behavior. Previous data from our group show circadian disruption in rats given access to heroin during the light phase, which is important because circadian disruption, itself, can increase drug intake. Thus, the goal of this experiment was to determine how time of day of access affects heroin self-administration and the development of addiction-like behaviors including escalation of heroin intake, willingness to work for heroin on a progressive ratio schedule of reinforcement, seeking during extinction, incubation of seeking, and reinstatement of heroin-seeking behavior.

MATERIALS AND METHODS

Male Sprague Dawley rats were given the opportunity to self-administer heroin for 6 h per trial during the second half of either the light or dark phase for 18 trials, including one progressive ratio challenge. Rats then underwent 14 days of abstinence, with a 5-h extinction test occurring on both the first and the 14th days of abstinence. The second extinction test was followed by a heroin prime and 1 h of reinstatement testing. On the following day, a subset of rats were tested in an additional extinction test where rats were tested either at the same time of the day as their previous self-administration sessions or during the opposite light/dark phase.

RESULTS

Relative to Light Access rats, Dark Access rats took more heroin, exhibited more goal-directed behavior, exhibited more seeking during the dark phase, failed to extinguish seeking during the 5-h extinction test in the dark phase, and exhibited greater incubation of heroin seeking following abstinence. However, Dark Access rats did not escalate drug taking over trials, work harder for drug, or seek more during drug-induced reinstatement than Light Access rats.

CONCLUSIONS

These results show that time of access to heroin affects overall heroin intake and seeking in extinction, but does not affect other addiction-like behaviors in rats.

Exposure to environmental enrichment attenuates addiction-like behavior and alters molecular effects of heroin self-administration in rats

Environmental factors profoundly affect the addictive potential of drugs of abuse and may also modulate the neuro-anatomical/neuro-chemical impacts of uncontrolled drug use and relapse propensity. This study examined the impact of environmental enrichment on heroin self-administration, addiction-related behaviors, and molecular processes proposed to underlie these behaviors. Male Sprague-Dawley rats in standard and enriched housing conditions intravenously self-administered similar amounts of heroin over 14 days. However, environmental enrichment attenuated progressive ratio, extinction, and reinstatement session responding after 14 days of enforced abstinence. Molecular mechanisms, namely DNA methylation and gene expression, are proposed to underlie abstinence-persistent behaviors. A global reduction in methylation is reported to coincide with addiction, but no differences in total genomic methylation or repeat element methylation were observed in CpG or non-CpG (CH) contexts across the mesolimbic circuitry as assessed by multiple methods including whole genome bisulfite sequencing. Immediate early gene expression associated with drug seeking, taking, and abstinence also were examined. EGR1 and EGR2 were suppressed in mesolimbic regions with heroin-taking and environmental enrichment. Site-specific methylation analysis of EGR1 and EGR2 promoter regions using bisulfite amplicon sequencing (BSAS) revealed hypo-methylation in the EGR2 promoter region and EGR1 intragenic CpG sites with heroin-taking and environmental enrichment that was associated with decreased mRNA expression. Taken together, these findings illuminate the impact of drug taking and environment on the epigenome in a locus and gene-specific manner and highlight the need for positive, alternative rewards in the treatment and prevention of drug addiction.