Effects of rapid eye movement (REM) sleep deprivation on pain sensitivity in the rat

Estrogen receptor α regulates the IKKs/NF-kB activity involved in the development of mechanical allodynia induced by REM sleep deprivation in rats

Several signaling pathways that converge in NF-kB activation have been linked to developing and maintaining different types of pathological pain. In addition, some mechanisms implied in the establishment of chronic pain have been demonstrated to have a sex-dependent correlation. This study aimed to determine if the IKKs/NF-kB signaling pathway is involved in establishing REM sleep deprivation (REMSD) induced mechanical allodynia in rats and its possible regulation depending on estradiol and estrogen receptors. Intrathecal administration of BMS-345541 or minocycline, two drugs that reduce the IKKs/NF-kB activity, avoided the development of mechanical allodynia in female but not in male rats subjected to 48 h of REMSD. Ovariectomy in female rats abolished the effect of BMS-345541 and minocycline. Meanwhile, the 17-β-estradiol restitution restored it. Intrathecal administration of MPP, a selective ERα antagonist, but not PHTPP, a selective ERβ antagonist, avoided the effect of BMS-345541 in female rats without hormonal manipulation. In addition, the transient run-down of ERα in female rats abolished the effect of BMS-345541. All data suggest an important role of ERα as a regulator of the IKKs/NF-kB activity. REMSD increased the ERα protein expression in the dorsal root ganglia and the dorsal spinal cord in females but not in male rats. Interestingly, ERα activation or ERα overexpression allowed the effect of BMS-345541 in male rats. Data suggest an important regulatory role of ERα in the IKKs/NF-kB activity on establishing mechanical allodynia induced by REMSD in female rats.

Chronic REM sleep deprivation leads to manic- and OCD-related behaviors, and decreases hippocampal BDNF expression in female rats

BACKGROUND

Rapid-eye movement (REM) sleep deprivation (SD) can induce manic-like behaviors in rodents. On the other hand, lithium, as one of the oldest drugs used in neuropsychiatric disorders, is still one of the best drugs for the treatment and control of bipolar disorder. In this study, we aimed to investigate the role of chronic short-term REM SD in the induction of manic-like behaviors in female rats.

METHODS

The rats were exposed to REM SD for 14 days (6 hours/day). Lithium was intraperitoneally injected at the doses of 10, 50, and 100 mg/kg.

RESULTS

REM SD induced hyperactivity and OCD-like behavior, and decreased anxiety, depressive-like behavior, and pain subthreshold. REM SD also impaired passive avoidance memory and decreased hippocampal brain-derived neurotrophic factor (BDNF) expression level. Lithium at the doses of 50 and 100 mg/kg partly and completely abolished these effects, respectively. However, lithium (100 mg/kg) increased BDNF expression level in control and sham REM SD rats with no significant changes in behavior.

CONCLUSIONS

Chronic short-term REM SD may induce a mania-like model and lead to OCD-like behavior and irritability. In the present study, we demonstrated a putative rodent model of mania induced by chronic REM SD in female rats. We suggest that future studies should examine behavioral and mood changes following chronic REM SD in both sexes. Furthermore, the relationship between manic-like behaviors and chronic REM SD should be investigated.

The effect of REM-sleep disruption on affective processing: A systematic review of human and animal experimental studies

Evidence on the importance of rapid-eye-movement sleep (REMS) in processing emotions is accumulating. The focus of this systematic review is the outcomes of experimental REMS deprivation (REMSD), which is the most common method in animal models and human studies on REMSD. This review revealed that variations in the applied REMSD methods were substantial. Animal models used longer deprivation protocols compared with studies in humans, which mostly reported acute deprivation effects after one night. Studies on animal models showed that REMSD causes aggressive behavior, increased pain sensitivity, reduced sexual behavior, and compromised consolidation of fear memories. Animal models also revealed that REMSD during critical developmental periods elicits lasting consequences on affective-related behavior. The few human studies revealed increases in pain sensitivity and suggest stronger consolidation of emotional memories after REMSD. As pharmacological interventions (such as selective serotonin reuptake inhibitors [SSRIs]) may suppress REMS for long periods, there is a clear gap in knowledge regarding the effects and mechanisms of chronic REMS suppression in humans.

Pretreatment of the ROS Inhibitor Phenyl-N-tert-butylnitrone Alleviates Sleep Deprivation-Induced Hyperalgesia by Suppressing Microglia Activation and NLRP3 Inflammasome Activity in the Spinal Dorsal Cord

Sleep deprivation, a common perioperative period health problem, causes ocular discomfort and affects postsurgical pain. However, the mechanism of sleep deprivation-induced increased pain sensitivity is elusive. This study aims to explore the role of ROS in sleep deprivation (SD)-induced hyperalgesia and the underlying mechanism. A 48-h continuous SD was performed prior to the hind paw incision pain modeling in mice. We measured ROS levels, microglial activation, DNA damage and protein levels of iNOS, NLRP3, p-P65 and P65 in mouse spinal dorsal cord. The involvement of ROS in SD-induced prolongation of postsurgical pain was further confirmed by intrathecal injection of ROS inhibitor, phenyl-N-tert-butylnitrone (PBN). Pretreatment of 48-h SD in mice significantly prolonged postsurgical pain recovery, manifesting as lowered paw withdrawal mechanical threshold and paw withdrawal thermal latency. It caused ROS increase and upregulation of iNOS on both Day 1 and 7 in mouse spinal dorsal cord. In addition, upregulation of NLRP3 and p-P65, microglial activation and DNA damage were observed in mice pretreated with 48-h SD prior to the incision. Notably, intrathecal injection of PBN significantly reversed the harmful effects of SD on postsurgical pain recovery, hyperalgesia, microglial activation and DNA damage via the NF-κB signaling pathway. Collectively, ROS increase is responsible for SD-induced hyperalgesia through activating microglial, triggering DNA damage and enhancing NLRP3 inflammasome activity in the spinal dorsal cord.

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.

The Relationship Between Circadian Typology and Dry Eye Symptoms in Chinese College Students

PURPOSE

To explore the relationship between symptomatic dry eye and circadian typology in college students.

METHODS

This study included 269 students from 3 Chinese universities. All participants completed the ocular surface disease index (OSDI) questionnaire, the morningness-eveningness questionnaire (MEQ), and the Pittsburgh sleep quality index (PSQI) questionnaire. Participants were grouped into 3 types by the reduced MEQ (rMEQ) score:E-Type, N-Type, and M-Type. All these parameters were then analyzed for the effect on the severity of dry eye.

RESULTS

The occurrence rates of poor sleep quality (PSQI>5) and symptomatic dry eye (OSDI > 13) in the college students were 53.2% and 40.2%, respectively. The distribution of the circadian typology differed significantly among the college students with different dry eye severities (χ ² = 59.44, P = 0. 000), and E-type was associated with the most severe dry eye symptoms. The OSDI and PSQI scores were both significantly different among college students with different chronotypes (F = 22.14, P = 0.000; F = 15.21, P = 0.000; respectively). For both scores, the E-type scored the highest, followed by N-type, and M-type was the lowest. The circadian typology was an independent factor for dry eye. The risk of E-Type was 6.99 times higher than that of M-Type (P = 0.000), and the risk of N-types was 3.23 times higher than that of M-Type (P = 0.000). Sleep quality was also an independent risk factor for dry eye (P = 0.000). Gender and awareness of dry eye were not risk factors for dry eye.

CONCLUSION

The severity of dry eye symptoms and sleep quality were associated with different circadian typologies. The more the circadian preference tended to be E-type, the worse the sleep quality and the more serious dry eye symptoms would appear.

The Association Between Dry Eye and Sleep Disorders: The Evidence and Possible Mechanisms

Dry eye is a disease that severely affects patients' quality of life, increasing the global burden on public health and finance. There is growing evidence that a poor lifestyle is a significant risk factor for dry eye. Along with the development of society, sleep, as a way of life, is also constantly changing. The main manifestations of sleep disorders are reduced sleep time, circadian rhythm disturbances, and sleep breathing disturbances. Sleep disorders and their secondary systemic diseases have attracted wide attention in recent years. This review mainly explored the correlation between sleep disorders and dry eye, and found that sleep-related problems and other factors potentially leading from sleep disorders could be critical factors for dry eye. These results suggest that ophthalmologists should pay attention to the sleep health problems in patients with dry eye, and we hope that this paper can provide help for future research in this field.

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.

Noninvasive vagus nerve stimulation and morphine transiently inhibit trigeminal pain signaling in a chronic headache model

Noninvasive vagus nerve stimulation suppressed persistent trigeminal nociception in a chronic headache model similarly to morphine and may provide a safe, nonaddictive abortive therapy for chronic headache.

Introduction:

Chronic headache conditions are characterized by persistent sensitization of the trigeminal system, which involves dysfunction of descending pain modulation. We previously reported that noninvasive vagus nerve stimulation (nVNS) inhibits trigeminal nociception in models of episodic migraine through a mechanism involving enhanced serotonergic and GABAergic descending pain signaling.

Objectives:

The analgesic effectiveness of nVNS and morphine were investigated in an animal model of chronic headache mediated by the combination of the 3 migraine risk factors of neck muscle tension, paradoxical sleep deprivation, and pungent odors.

Methods:

Sprague–Dawley rats were injected with complete Freund's adjuvant in the trapezius and sleep deprived for 1 night to promote trigeminal sensitization. After 7 days, animals were exposed to a pungent odor, and mechanical nocifensive head withdrawal responses were determined using von Frey filaments. Beginning on day 3 after odor exposure, animals were treated daily with either nVNS or morphine for 7 days.

Results:

Exposure of animals sensitized by neck inflammation and sleep deprivation to a pungent odor resulted in a prolonged state of trigeminal nociception. Daily administration of nVNS or morphine significantly repressed the nocifensive response; however, cessation resulted in a return to heightened pretreatment nocifensive levels.

Conclusions:

The combination of reported migraine risk factors promotes a state of sustained trigeminal hypersensitivity characteristic of chronic headache. Daily nVNS was similarly effective as morphine in inhibiting nociception and may represent a safer, opioid-sparing therapeutic option for other chronic pain disorders involving sensitization of the trigeminal system by promoting descending pain modulation.

Sleep Deprivation and Neurological Disorders

Sleep plays an important role in maintaining neuronal circuitry, signalling and helps maintain overall health and wellbeing. Sleep deprivation (SD) disturbs the circadian physiology and exerts a negative impact on brain and behavioural functions. SD impairs the cellular clearance of misfolded neurotoxin proteins like α-synuclein, amyloid-β, and tau which are involved in major neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. In addition, SD is also shown to affect the glymphatic system, a glial-dependent metabolic waste clearance pathway, causing accumulation of misfolded faulty proteins in synaptic compartments resulting in cognitive decline. Also, SD affects the immunological and redox system resulting in neuroinflammation and oxidative stress. Hence, it is important to understand the molecular and biochemical alterations that are the causative factors leading to these pathophysiological effects on the neuronal system. This review is an attempt in this direction. It provides up-to-date information on the alterations in the key processes, pathways, and proteins that are negatively affected by SD and become reasons for neurological disorders over a prolonged period of time, if left unattended.

Differential Gene Expression in Brain and Liver Tissue of Wistar Rats after Rapid Eye Movement Sleep Deprivation

Sleep is essential for the survival of most living beings. Numerous researchers have identified a series of genes that are thought to regulate "sleep-state" or the "deprived state". As sleep has a significant effect on physiology, we believe that lack of total sleep, or particularly rapid eye movement (REM) sleep, for a prolonged period would have a profound impact on various body tissues. Therefore, using the microarray method, we sought to determine which genes and processes are affected in the brain and liver of rats following nine days of REM sleep deprivation. Our findings showed that REM sleep deprivation affected a total of 652 genes in the brain and 426 genes in the liver. Only 23 genes were affected commonly, 10 oppositely, and 13 similarly across brain and liver tissue. Our results suggest that nine-day REM sleep deprivation differentially affects genes and processes in the brain and liver of rats.

Sleep deprivation of rats increases postsurgical expression and activity of L-type calcium channel in the dorsal root ganglion and slows recovery from postsurgical pain

Perioperative sleep disturbance is a risk factor for persistent pain after surgery. Clinical studies have shown that patients with insufficient sleep before and after surgery experience more intense and long-lasting postoperative pain. We hypothesize that sleep deprivation alters L-type calcium channels in the dorsal root ganglia (DRG), thus delaying the recovery from post-surgical pain. To verify this hypothesis, and to identify new predictors and therapeutic targets for persistent postoperative pain, we first established a model of postsurgical pain with perioperative sleep deprivation (SD) by administering hind paw plantar incision to sleep deprivation rats. Then we conducted behavioral tests, including tests with von Frey filaments and a laser heat test, to verify sensory pain, measured the expression of L-type calcium channels using western blotting and immunofluorescence of dorsal root ganglia (an important neural target for peripheral nociception), and examined the activity of L-type calcium channels and neuron excitability using electrophysiological measurements. We validated the findings by performing intraperitoneal injections of calcium channel blockers and microinjections of dorsal root ganglion cells with adeno-associated virus. We found that short-term sleep deprivation before and after surgery increased expression and activity of L-type calcium channels in the lumbar dorsal root ganglia, and delayed recovery from postsurgical pain. Blocking these channels reduced impact of sleep deprivation. We conclude that the increased expression and activity of L-type calcium channels is associated with the sleep deprivation-mediated prolongation of postoperative pain. L-type calcium channels are thus a potential target for management of postoperative pain.

The role of 5-HT4 serotonin receptors in the CA1 hippocampal region on memory acquisition impairment induced by total (TSD) and REM sleep deprivation (RSD)

Sleep is a circadian rhythm that is modulated by endogenous circadian clock located in the suprachiasmatic nucleus (SCN). Sleep modulates memory acquisition and promotes memory consolidation. Studies have shown that sleep deprivation (SD) impairs different types of memory including passive avoidance. Furthermore, the hippocampus plays a significant role in modulating passive avoidance memory. On the other hand, 5-HT4 receptors are expressed in the hippocampus and involved in learning and memory processes. In this study, we aimed to investigate the role of CA1 hippocampal 5-HT4 receptors in memory acquisition impairment induced by total sleep deprivation (TSD: 24 h) and REM sleep deprivation (RSD: 24 h). The water box apparatus was used to induce TSD, while multi-platform apparatus was applied to induce RSD. Passive avoidance memory test was also used to evaluate memory acquisition. The results showed that, intra-CA1 pre-training injection of RS67333 (5-HT4 agonist) and RS23597 (5-HT4 antagonist) at the doses of 0.01 and 0.1 µg/rat decreased memory acquisition, but did not alter pain perception and locomotor activity. Furthermore, TSD and RSD decreased memory acquisition; however, only TSD decreased locomotor activity and induced analgesic effect. The sub-threshold doses of RS67333 and RS23597, 0.001 and 0.0001 µg/rat, respectively, reversed the effect of TSD on memory acquisition and locomotor activity. In addition, only RS23597 reversed TSD-induced analgesia. In RSD condition, the subthreshold dose of RS23597 improved RSD-induced memory acquisition deficit. In conclusion, CA1 hippocampal 5-HT4 receptors play an important role in TSD/RSD-induced cognitive alterations.

Psychological Sleep Interventions for Migraine and Tension-Type Headache: A Systematic Review and Meta-Analysis

Disordered sleep, poor sleep quality, and insufficient or excessive sleep duration are known triggers of primary and secondary headaches. Given this, it is plausible that improving sleep will subsequently reduce headache activity. We report a systematic review of the literature, examining studies utilising psychological sleep interventions for the treatment of migraine and tension-type headache. PubMed, EMBASE, CINAHL, PsycINFO, and Cochrane Central were searched, using terms pertaining to psychological sleep interventions and headaches. Meta-analysis was performed for two outcome measures; headache frequency, and headache intensity. 103 studies were retrieved, of which 55 were duplicates. After completing reviews, three studies were retained. An additional eligible study was published after the initial search, and was found via monthly update searches, resulting in a total of four included studies. The effects of psychological sleep interventions (and in one study, combined with drug therapy) significantly reduced headache frequency and headache intensity. Three studies improved various sleep outcomes such as duration, efficiency, and excessive sleepiness. Psychological sleep interventions improve headache frequency and sleep, however there is conflicting evidence for the effect on headache intensity between studies. Limitations include the small number of studies conducted to date. Despite this, the notable improvements in headaches and sleep achieved after psychological sleep interventions indicates further research on this promising topic is warranted.

Effects of prolonged paradoxical sleep deprivation with or without acute cold stress on hemodynamic perturbations in rats

Prolonged paradoxical sleep deprivation (PSD) and cold stress (CS) are known to cause sympathoexcitation and increase the risk of cardiovascular disease. The present study examined the effect of PSD with CS on hemodynamic perturbations by investigating blood pressure and heart rate variability (BPV and HRV) in conscious rats. Adult male Sprague-Dawley rats were divided into three groups (n = 10, each): normal sleep (NS), PSD of 72 h, and recovery sleep of 7 days after PSD. When compared with NS, PSD increased systolic blood pressure in all three conditions: before CS (PreCS), CS, and after CS (PostCS). The PSD also increased heart rate in both PreCS and PostCS. Furthermore, spectral power changes were observed throughout the experiment. The PSD increased very-low-frequency BPV in PreCS, decreased very-low-frequency HRV in CS, and increased low-frequency BPV in all three conditions. The PSD increased low-frequency HRV in PreCS, increased high-frequency BPV in both CS and PostCS, and also increased high-frequency HRV in both PreCS and CS but decreased that in PostCS. On the other hand, when compared with PSD, recovery sleep has reversed most cardiovascular changes in PSD toward the NS level. However, when compared with NS, spectral powers of very-low-frequency BPV in the recovery phase showed a lower level. These results showed that in the resting condition, PSD might evoke sympathoexcitation with a tendency to increase both very-low-frequency BPV and very-low-frequency HRV, as the intensified myogenic oscillations. However, in the CS condition, PSD evoked the sympathoexcitation yet might attenuate such myogenic oscillations.

Nicotine and sleep deprivation: impact on pain sensitivity and immune modulation in rats

Repeated nicotine administration has been associated with increased paradoxical sleep in rats and antinociceptive properties, whereas paradoxical sleep deprivation (PSD) elicits pronociceptive and inflammatory responses. Thus, we aimed to evaluate the effect of repeated nicotine administration and its withdrawal combined with PSD on pain sensitivity and inflammatory markers. Sixty adult male Wistar rats were subjected to repeated injections of saline (SAL) or nicotine (NIC) for 12 days or 7 days of nicotine followed by acute mecamylamine administration on day 8 to precipitate nicotine abstinence (ABST). On day 9, the animals were submitted to PSD for 72 h or remained in control condition (CTRL); on day 12, thermal pain threshold was assessed by the hot plate test. PSD significantly decreased the latency to paw withdrawal in all groups compared to their respective controls. ABST-PSD animals presented higher levels of interleukin (IL)-6 compared to all groups, except ABST-CTRL. After adjustment for weight loss, IL-6, IL-4 and tumor necrosis factor alpha, ABST-PSD was associated with the lowest pain threshold. Nicotine and IL-4 levels were predictors of higher pain threshold. Hyperalgesia induced by PSD prevailed over the antinociceptive action of nicotine, while the association between PSD and ABST synergistically increased IL-6 concentrations and decreased pain threshold.

Preemptive Caffeine Administration Blocks the Increase in Postoperative Pain Caused by Previous Sleep Loss in the Rat: A Potential Role for Preoptic Adenosine A2A Receptors in Sleep-Pain Interactions

Sleep and pain are reciprocally related, but the precise mechanisms underlying this relationship are poorly understood. This study used a rat model of surgical pain to examine the effect of previous sleep loss on postoperative pain and tested the hypothesis that preoptic adenosinergic mechanisms regulate sleep-pain interactions. Relative to ad libitum sleep, 6 hours of total sleep deprivation prior to a surgical incision significantly enhanced postoperative mechanical hypersensitivity in the affected paw and prolonged the time to recovery from surgery. There were no sex-specific differences in these measures. There were also no changes in adrenocorticotropic hormone and corticosterone levels after sleep deprivation, suggesting that this effect was not mediated by the stress associated with the sleep perturbation. Systemic administration of the nonselective adenosine receptor antagonist caffeine at the onset of sleep deprivation prevented the sleep deprivation-induced increase in postoperative hypersensitivity. Microinjection of the adenosine A2A receptor antagonist ZM 241385 into the median preoptic nucleus (MnPO) blocked the increase in surgical pain levels and duration caused by prior sleep deprivation and eliminated the thermal hyperalgesia induced by sleep deprivation in a group of nonoperated (i.e., without surgical incision) rats. These data show that even a brief sleep disturbance prior to surgery worsens postoperative pain and are consistent with our hypothesis that adenosine A2A receptors in the MnPO contribute to regulate these sleep-pain interactions.

Chronic Pain and Sleep Disorders in Primary Care

BACKGROUND

Chronic pain (CP) and sleep disorders (SD) are highly prevalent in the general population. However, comprehensive data regarding the prevalence and characteristics of pain and SD in primary care are rare.

METHODS

From N = 578 patients N = 570 were included within 8 weeks (mean age: 50.8 ± 18.7 years, females: 289). Sociodemographic data, Insomnia Severity Index (ISI), and parts of a self-report questionnaire for pain (Multidimensional German Pain Questionnaire) were recorded and additional medical information (pain medication, sleep medication) was gathered from the patient charts.

RESULTS

Of the total sample, 33.2% (n = 189) suffer from CP (pain ≥ 6 months) and 29.1% (n = 166) from SD. 45.5% of the CP patients suffer from SD and 26.5% from clinical insomnia (ISI ≥ 15). SD (β = 0.872, SE = 0.191,  t = 4,572, p < 0.001, CI [0.497; 1.246]) and older age (β = 0.025, SE = 0.005, t = 5.135, p < 0.001, CI [0.015; 0.035]) were significantly associated with pain experience.

CONCLUSION

About a quarter of CP patients suffer from clinical insomnia. The suggested bidirectional relation should be considered during comprehensive assessment and treatment of patients.

Decreased alertness due to sleep loss increases pain sensitivity in mice

Extended daytime and nighttime activities are major contributors to the growing sleep deficiency epidemic, as is the high prevalence of sleep disorders like insomnia. The consequences of chronic insufficient sleep for health remain uncertain. Sleep quality and duration predict presence of pain the next day in healthy subjects, suggesting that sleep disturbances alone may worsen pain, and experimental sleep deprivation in humans supports this claim. We demonstrate that sleep loss, but not sleep fragmentation, in healthy mice increases sensitivity to noxious stimuli (referred to as 'pain') without general sensory hyper-responsiveness. Moderate daily repeated sleep loss leads to a progressive accumulation of sleep debt and also to exaggerated pain responses, both of which are rescued after restoration of normal sleep. Caffeine and modafinil, two wake-promoting agents that have no analgesic activity in rested mice, immediately normalize pain sensitivity in sleep-deprived animals, without affecting sleep debt. The reversibility of mild sleep-loss-induced pain by wake-promoting agents reveals an unsuspected role for alertness in setting pain sensitivity. Clinically, insufficient or poor-quality sleep may worsen pain and this enhanced pain may be reduced not by analgesics, whose effectiveness is reduced, but by increasing alertness or providing better sleep.

Is increased spinal nociception another hallmark for Parkinson's disease?

Augmented spinal nociception during the "off" phase has been observed early in Parkinson's disease further increasing with disease duration. To find out whether increased spinal nociception represents a premotor feature, experimental pain sensitivity was assessed in idiopathic REM-sleep behavior disorder (IRBD) patients with or without signs of a neurodegenerative disorder compared to early Parkinson's disease (ePD) patients and healthy controls (HC). Spinal nociception as measured by the nociceptive flexion reflex (NFR) and experimental pain sensitivity as measured by heat and electrical pain thresholds were determined in 14 IRBD, 15 ePD patients in the medication-defined "off" state and 27 HC in an explorative cohort study. No significant differences between IRBD and HC were found with regard to spinal nociception (NFR) and experimental pain sensitivity. However, IRBD patient with anosmia and/or abnormal DaTSCAN tended to increased experimental pain sensitivity. In contrast, early PD patients exhibited increased NFR responses compared to HC, and a tendency for increased spinal nociception compared to IRBD patients. Increased spinal nociception may represent an early but not a premotor, non-motor feature of PD. Whether increased pain sensitivity already presents a premotor feature should be assessed in further studies.

Polysomnographic Measurement of Sleep Duration and Bodily Pain Perception in the Sleep Heart Health Study

STUDY OBJECTIVES

To determine whether total sleep time (TST) and specific sleep stage duration are associated with bodily pain perception and whether sex, age, or subjective sleepiness modifies this relationship.

METHODS

Data from adults ages 39-90 y (n = 5,199) who took part in the Sleep Heart Health Study Exam 1 were analyzed. TST, rapid eye movement (REM) sleep time, and slow wave sleep (SWS) time were measured by unattended, in-home nocturnal polysomnography. Bodily pain perception was measured via the Short Form-36 questionnaire bodily pain component. We used logistic regression to examine associations between total and individual sleep stage durations and bodily pain perception controlling for age, sex, race, body mass index, apnea-hypopnea index, antidepressant use, and important cardiovascular conditions (smoking [pack-years], history of diabetes, and history of percutaneous coronary intervention and/or coronary artery bypass graft).

RESULTS

In the fully adjusted model, REM sleep time and SWS time were not associated with "moderate to severe pain," whereas TST was: Each 1-h decrement in TST was associated with a 7% increased odds of "moderate to severe pain" (odds ratio 1.07, 95% confidence interval 1.002, 1.14). Due to modification of the association between SWS time and "moderate to severe pain" by sex (P for interaction = 0.01), we performed analyses stratified by sex: Each 1-h decrement in SWS time was associated with a 20% higher odds of "moderate to severe pain" among men (odds ratio 1.20, 95% confidence interval 1.03-1.42) whereas an association was not observed among women.

CONCLUSIONS

Shorter TST among all subjects and shorter SWS time in men was associated with "moderate to severe pain." REM sleep time was not associated with bodily pain perception in this cohort.

Sleep Deprivation and Recovery Sleep Prior to a Noxious Inflammatory Insult Influence Characteristics and Duration of Pain

STUDY OBJECTIVES

Insufficient sleep and chronic pain are public health epidemics. Sleep loss worsens pain and predicts the development of chronic pain. Whether previous, acute sleep loss and recovery sleep determine pain levels and duration remains poorly understood. This study tested whether acute sleep deprivation and recovery sleep prior to formalin injection alter post-injection pain levels and duration.

METHODS

Male Sprague-Dawley rats (n = 48) underwent sleep deprivation or ad libitum sleep for 9 hours. Thereafter, rats received a subcutaneous injection of formalin or saline into a hind paw. In the recovery sleep group, rats were allowed 24 h between sleep deprivation and the injection of formalin. Mechanical and thermal nociception were assessed using the von Frey test and Hargreaves' method. Nociceptive measures were performed at 1, 3, 7, 10, 14, 17 and 21 days post-injection.

RESULTS

Formalin caused bilateral mechanical hypersensitivity (allodynia) that persisted for up to 21 days post-injection. Sleep deprivation significantly enhanced bilateral allodynia. There was a synergistic interaction when sleep deprivation preceded a formalin injection. Rats allowed a recovery sleep period prior to formalin injection developed allodynia only in the injected limb, with higher mechanical thresholds (less allodynia) and a shorter recovery period. There were no persistent changes in thermal nociception.

CONCLUSION

The data suggest that acute sleep loss preceding an inflammatory insult enhances pain and can contribute to chronic pain. The results encourage studies in a model of surgical pain to test whether enhancing sleep reduces pain levels and duration.

Short-Term Sleep Disturbance-Induced Stress Does not Affect Basal Pain Perception, but Does Delay Postsurgical Pain Recovery

Chronic sleep disturbance-induced stress is known to increase basal pain sensitivity. However, most surgical patients frequently report short-term sleep disturbance/deprivation during the pre- and postoperation periods and have normal pain perception presurgery. Whether this short-term sleep disturbance affects postsurgical pain is elusive. Here, we report that pre- or postexposure to rapid eye movement sleep disturbance (REMSD) for 6 hours daily for 3 consecutive days did not alter basal responses to mechanical, heat, and cold stimuli, but did delay recovery in incision-induced reductions in paw withdrawal threshold to mechanical stimulation and paw withdrawal latencies to heat and cold stimuli on the ipsilateral side of male or female rats. This short-term REMSD led to stress shown by an increase in swim immobility time, a decrease in sucrose consumption, and an increase in the level of corticosterone in serum. Blocking this stress via intrathecal RU38486 or bilateral adrenalectomy abolished REMSD-caused delay in recovery of incision-induced reductions in behavioral responses to mechanical, heat, and cold stimuli. Moreover, this short-term REMSD produced significant reductions in the levels of mu opioid receptor and kappa opioid receptor, but not Kv1.2, in the ipsilateral L4/5 spinal cord and dorsal root ganglia on day 9 after incision (but not after sham surgery).

PERSPECTIVE

Our findings show that short-term sleep disturbance either pre- or postsurgery does not alter basal pain perception, but does exacerbate postsurgical pain hypersensitivity. The latter may be related to the reductions of mu and kappa opioid receptors in the spinal cord and dorsal root ganglia caused by REMSD plus incision. Prevention of short-term sleep disturbance may help recovery from postsurgical pain in patients.

Effect of a sleep aid in analgesia after arthroscopic rotator cuff repair

PURPOSE

The aim of this study was to evaluate the effects and safety of a sleep aid for postoperative analgesia in patients undergoing arthroscopic rotator cuff repair.

MATERIALS AND METHODS

Seventy-eight patients were prospectively assigned to either the zolpidem group (multimodal analgesia+zolpidem; 39 patients) or the control group (multimodal analgesia; 39 patients). Self-rated pain levels were assessed twice a day using a visual analog scale (VAS). The need for additional rescue analgesic, duration of functional recovery, and adverse effects were assessed for the first 5 days after surgery.

RESULTS

The mean number of times that additional rescue analgesic was required during 5 days after surgery was 2.1±2.0 in the zolpidem group and 3.3±2.8 in the control group, a significant difference. There were no significant differences between the two groups in mean VAS pain scores during the first 5 days after surgery, although the zolpidem group had lower VAS pain scores than the control group. Additionally, there were no significant differences in duration of functional recovery and adverse effects between the two groups.

CONCLUSION

The use of zolpidem for analgesia after arthroscopic rotator cuff repair provided a significant reduction in the need for rescue analgesic without increasing adverse effects. Nevertheless, mean VAS pain scores during the first 5 days after surgery did not differ between the zolpidem group and the control group.

Development and pharmacological characterization of a model of sleep disruption-induced hypersensitivity in the rat

BACKGROUND

Sleep disturbance is a commonly reported co-morbidity in chronic pain patients, and conversely, disruption of sleep can cause acute and long-lasting hypersensitivity to painful stimuli. The underlying mechanisms of sleep disruption-induced pain hypersensitivity are poorly understood. Confounding factors of previous studies have been the sleep disruption protocols, such as the 'pedestal over water' or 'inverted flower pot' methods, that can cause large stress responses and therefore may significantly affect pain outcome measures.

METHODS

Sleep disruption was induced by placing rats for 8 h in a slowly rotating cylindrical cage causing arousal via the righting reflex. Mechanical (Von Frey filaments) and thermal (Hargreaves) nociceptive thresholds were assessed, and plasma corticosterone levels were measured (mass spectroscopy). Sleep disruption-induced hypersensitivity was pharmacologically characterized with drugs relevant for pain treatment, including gabapentin (30 mg/kg and 50 mg/kg), Ica-6p (Kv7.2/7.3 potassium channel opener; 10 mg/kg), ibuprofen (30 mg/kg and 100 mg/kg) and amitriptyline (10 mg/kg).

RESULTS

Eight hours of sleep disruption caused robust mechanical and heat hypersensitivity in the absence of a measurable change in plasma corticosterone levels. Gabapentin had no effect on reduced nociceptive thresholds. Ibuprofen attenuated mechanical thresholds, while Ica-6p and amitriptyline attenuated only reduced thermal nociceptive thresholds.

CONCLUSIONS

These results show that acute and low-stress sleep disruption causes mechanical and heat hypersensitivity in rats. Mechanical and heat hypersensitivity exhibited differential sensitivity to pharmacological agents, thus suggesting dissociable mechanisms for those two modalities. Ultimately, this model could help identify underlying mechanisms linking sleep disruption and hypersensitivity.

Sleep deprivation aggravates median nerve injury-induced neuropathic pain and enhances microglial activation by suppressing melatonin secretion

STUDY OBJECTIVES

Sleep deprivation is common in patients with neuropathic pain, but the effect of sleep deprivation on pathological pain remains uncertain. This study investigated whether sleep deprivation aggravates neuropathic symptoms and enhances microglial activation in the cuneate nucleus (CN) in a median nerve chronic constriction injury (CCI) model. Also, we assessed if melatonin supplements during the sleep deprived period attenuates these effects.

DESIGN

Rats were subjected to sleep deprivation for 3 days by the disc-on-water method either before or after CCI. In the melatonin treatment group, CCI rats received melatonin supplements at doses of 37.5, 75, 150, or 300 mg/kg during sleep deprivation. Melatonin was administered at 23:00 once a day.

PARTICIPANTS

Male Sprague-Dawley rats, weighing 180-250 g (n = 190), were used.

MEASUREMENTS

Seven days after CCI, behavioral testing was conducted, and immunohistochemistry, immunoblotting, and enzyme-linked immunosorbent assay were used for qualitative and quantitative analyses of microglial activation and measurements of proinflammatory cytokines.

RESULTS

In rats who underwent post-CCI sleep deprivation, microglia were more profoundly activated and neuropathic pain was worse than those receiving pre-CCI sleep deprivation. During the sleep deprived period, serum melatonin levels were low over the 24-h period. Administration of melatonin to CCI rats with sleep deprivation significantly attenuated activation of microglia and development of neuropathic pain, and markedly decreased concentrations of proinflammatory cytokines.

CONCLUSIONS

Sleep deprivation makes rats more vulnerable to nerve injury-induced neuropathic pain, probably because of associated lower melatonin levels. Melatonin supplements to restore a circadian variation in melatonin concentrations during the sleep deprived period could alleviate nerve injury-induced behavioral hypersensitivity.

Weighing the balance: how analgesics used in chronic pain influence sleep?

Pain and sleep share a bidirectional relationship, with each influencing the other. Several excellent reviews have explored this relationship. In this article, we revisit the evidence and explore existing research on this complex inter-relationship. The primary focus of the article is on the pharmacological treatment of chronic non-malignant pain and the main purpose is to review the effect of various pharmacological agents used in the management of chronic pain on sleep. This has not been comprehensively done before. We explore the clinical use of these agents, their impact on sleep architecture and sleep physiology, the mechanism of action on sleep parameters and sleep disorders associated with these agents. Pharmacological classes reviewed include antidepressants, opioid analgesics, anti-epileptics, cannabinoids and non-steroidal anti-inflammatory agents, drugs most commonly used to manage chronic pain. The objective is to help health professionals gain better insight into the complex effect that commonly used analgesics have on an individual's sleep and how this could impact on the effectiveness of the drug as an analgesic. We conclude that antidepressants have both positive and negative effects on sleep, so do opioids, but in the latter case the evidence shifts towards the counterproductive side. Some anticonvulsants are sleep sparing and non-steroidal anti-inflammatory drugs (NSAIDs) are sleep neutral. Cannabinoids remain an underexplored and researched group.

Reduced sleep, stress responsivity, and female sex contribute to persistent inflammation-induced mechanical hypersensitivity in rats

Studies in humans suggest that female sex, reduced sleep opportunities and biological stress responsivity increase risk for developing persistent pain conditions. To investigate the relative contribution of these three factors to persistent pain, we employed the Sciatic Inflammatory Neuritis (SIN) model of repeated left sciatic perineurial exposures to zymosan, an inflammatory stimulus, to determine their impact upon the development of persistent mechanical hypersensitivity. Following an initial moderate insult, a very low zymosan dose was infused daily for eight days to model a sub-threshold inflammatory perturbation to which only susceptible animals would manifest or maintain mechanical hypersensitivity. Using Sprague Dawley rats, maintaining wakefulness throughout the first one-half of the 12-h light phase resulted in a bilateral reduction in paw withdrawal thresholds (PWTs); zymosan infusion reduced ipsilateral PWTs in all animals and contralateral PWTs only in females. This sex difference was validated in Fischer 344, Lewis and Sprague Dawley rats, suggesting that females are the more susceptible phenotype for both local and centrally driven responses to repeated low-level inflammatory perturbations. Hypothalamic-pituitary-adrenal (HPA) axis hyporesponsive Lewis rats exhibited the most robust development of mechanical hypersensitivity and HPA axis hyperresponsive Fischer 344 rats matched the Lewis rats' mechanical hypersensitivity throughout the latter four days of the protocol. If HPA axis phenotype does indeed influence these findings, the more balanced responsivity of Sprague Dawley rats would seem to promote resilience in this paradigm. Taken together, these findings are consistent with what is known regarding persistent pain development in humans.

Recovery sleep does not mitigate the effects of prior sleep loss on paclitaxel-induced mechanical hypersensitivity in Sprague-Dawley rats

Society has a rapidly growing accumulative sleep debt due to employment obligations and lifestyle choices that limit sleep opportunities. The degree to which poor sleep may set the stage for adverse symptom outcomes among more than 1.7 million persons who will be diagnosed with cancer is not entirely understood. Paclitaxel (PAC), a commonly used chemotherapy agent, is associated with painful, debilitating peripheral neuropathy of the hands and feet, which may persist long after adjuvant therapy is completed. The aims of this preclinical study were to determine the accumulative and sustained effects of sleep restriction on PAC-induced mechanical sensitivity in animals and whether there are male-female differences in mechanical sensitivity in PAC-injected animals. Sixty-two adult Sprague-Dawley rats (n = 31 females) were assigned to three cycles of intraperitoneal injections of PAC (1 mg/kg) versus vehicle (VEH; 1 ml/kg) every other day at light onset for 7 days, followed by seven drug-free days and to sleep restriction versus unperturbed sleep. Sleep restriction involved gentle handling to maintain wakefulness during the first 6 hr of lights on immediately following an injection; otherwise, sleep was unperturbed. Mechanical sensitivity was assessed via von Frey filaments, using the up-down method. Mechanical sensitivity data were Log10 transformed to meet the assumption of normality for repeated measures analysis of variance. Chronic sleep restriction of the PAC-injected animals resulted in significantly increased mechanical sensitivity that progressively worsened despite sleep recovery opportunities. If these relationships hold in humans, targeted sleep interventions employed during a PAC protocol may improve pain outcomes.

[Pain prevalence in patients with and without OSAHS subjected to a polysomnogram: A cross-sectional study]

BACKGROUND AND OBJECTIVES

Sleep disturbances apparently have a negative effect on pain or the appearance of pain itself. This suggests the need to determine whether there could be a relationship between obstructive sleep apnea-hypopnea syndrome (OSAHS) and this phenomenon. The objective of this study was to determine the pain prevalence in a population who underwent polysomnography.

METHOD

A cross-sectional study of patients who underwent polisomnography, pain prevalence was measured with Mcgill pain questionnaire.

RESULTS

Data was obtained from 259 patients, and it was found that 69% suffered pain, and there was a prevalence of 81% OSAHS. Those with OSAHS had a 70% pain prevalence, with 64% for those without OSAHS.

CONCLUSIONS

A high pain prevalence was found this population, possibly related to the characteristic of the population, how the information was gathered, and not controlling for other illnesses related with pain.

Sleep fragmentation exacerbates mechanical hypersensitivity and alters subsequent sleep-wake behavior in a mouse model of musculoskeletal sensitization

STUDY OBJECTIVES

Sleep deprivation, or sleep disruption, enhances pain in human subjects. Chronic musculoskeletal pain is prevalent in our society, and constitutes a tremendous public health burden. Although preclinical models of neuropathic and inflammatory pain demonstrate effects on sleep, few studies focus on musculoskeletal pain. We reported elsewhere in this issue of SLEEP that musculoskeletal sensitization alters sleep of mice. In this study we hypothesize that sleep fragmentation during the development of musculoskeletal sensitization will exacerbate subsequent pain responses and alter sleep-wake behavior of mice.

DESIGN

This is a preclinical study using C57BL/6J mice to determine the effect on behavioral outcomes of sleep fragmentation combined with musculoskeletal sensitization.

METHODS

Musculoskeletal sensitization, a model of chronic muscle pain, was induced using two unilateral injections of acidified saline (pH 4.0) into the gastrocnemius muscle, spaced 5 days apart. Musculoskeletal sensitization manifests as mechanical hypersensitivity determined by von Frey filament testing at the hindpaws. Sleep fragmentation took place during the consecutive 12-h light periods of the 5 days between intramuscular injections. Electroencephalogram (EEG) and body temperature were recorded from some mice at baseline and for 3 weeks after musculoskeletal sensitization. Mechanical hypersensitivity was determined at preinjection baseline and on days 1, 3, 7, 14, and 21 after sensitization. Two additional experiments were conducted to determine the independent effects of sleep fragmentation or musculoskeletal sensitization on mechanical hypersensitivity.

RESULTS

Five days of sleep fragmentation alone did not induce mechanical hypersensitivity, whereas sleep fragmentation combined with musculoskeletal sensitization resulted in prolonged and exacerbated mechanical hypersensitivity. Sleep fragmentation combined with musculoskeletal sensitization had an effect on subsequent sleep of mice as demonstrated by increased numbers of sleep-wake state transitions during the light and dark periods; changes in nonrapid eye movement (NREM) sleep, rapid eye movement sleep, and wakefulness; and altered delta power during NREM sleep. These effects persisted for at least 3 weeks postsensitization.

CONCLUSIONS

Our data demonstrate that sleep fragmentation combined with musculoskeletal sensitization exacerbates the physiological and behavioral responses of mice to musculoskeletal sensitization, including mechanical hypersensitivity and sleep-wake behavior. These data contribute to increasing literature demonstrating bidirectional relationships between sleep and pain. The prevalence and incidence of insufficient sleep and pathologies characterized by chronic musculoskeletal pain are increasing in the United States. These demographic data underscore the need for research focused on insufficient sleep and chronic pain so that the quality of life for the millions of individuals with these conditions may be improved.

Nitric oxide modulates the hyperalgesic response to mechanical noxious stimuli in sleep-deprived rats

BACKGROUND

Sleep restriction alters pain perception in animals and humans, and many studies have indicated that paradoxical sleep deprivation (PSD) promotes hyperalgesia. The hyperalgesia observed after mechanical nociceptive stimulus is reversed through nitric oxide synthase (NOS) inhibition. Both nitric oxide (NO) and the dorsolateral periaqueductal gray matter (dlPAG) area of the brainstem are involved in hyperalgesia. Thus, in this work, we investigated the pain-related behavior response after mechanical noxious stimuli (electronic von Frey test), and the activity of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), an indicator of NOS activity, within the dlPAG of paradoxical sleep-deprived rats. We also evaluated the effects of pre-treatment with L-NAME on these parameters.

RESULTS

These data revealed that PSD reduced the hindpaw withdrawal threshold (-47%, p < 0.0001) confirming the hyperalgesic effect of this condition. In addition, there were more NADPH-d positive cells in dlPAG after PSD than in control rats (+ 59%, p < 0.0001). L-NAME treatment prevented the reduction in the hindpaw withdrawal threshold (+ 93%, p < 0.0001) and the increase in the NADPH-d positive cells number in the dlPAG of PSD-treated rats (-36%, p < 0.0001).

CONCLUSION

These data suggest that the hyperalgesic response to mechanical noxious stimuli in paradoxical sleep-deprived rats is associated with increased NOS activity in the dlPAG, which presumably influences the descending antinociceptive pathway.

One night of total sleep deprivation promotes a state of generalized hyperalgesia: a surrogate pain model to study the relationship of insomnia and pain

Sleep disturbances are highly prevalent in chronic pain patients. Understanding their relationship has become an important research topic since poor sleep and pain are assumed to closely interact. To date, human experimental studies exploring the impact of sleep disruption/deprivation on pain perception have yielded conflicting results. This inconsistency may be due to the large heterogeneity of study populations and study protocols previously used. In addition, none of the previous studies investigated the entire spectrum of nociceptive modalities. To address these shortcomings, a standardized comprehensive quantitative sensory protocol was used in order to compare the somatosensory profile of 14 healthy subjects (6 female, 8 male, 23.5 ± 4.1 year; mean ± SD) after a night of total sleep deprivation (TSD) and a night of habitual sleep in a cross-over design. One night of TSD significantly increased the level of sleepiness (P<0.001) and resulted in higher scores of the State Anxiety Inventory (P<0.01). In addition to previously reported hyperalgesia to heat (P<0.05) and blunt pressure (P<0.05), study participants developed hyperalgesia to cold (P<0.01) and increased mechanical pain sensitivity to pinprick stimuli (P<0.05) but no changes in temporal summation. Paradoxical heat sensations or dynamic mechanical allodynia were absent. TSD selectively modulated nociception, since detection thresholds of non-nociceptive modalities remained unchanged. Our findings show that a single night of TSD is able to induce generalized hyperalgesia and to increase State Anxiety scores. In the future, TSD may serve as a translational pain model to elucidate the pathomechanisms underlying the hyperalgesic effect of sleep disturbances.

Sleep disturbances are associated with increased pain, disease activity, depression, and anxiety in ankylosing spondylitis: a case-control study

Introduction

Literature data suggest that sleep disturbances are prevalent among patients with ankylosing spondylitis (AS) and have a close correlation with pain. Other studies indicate that sleep disturbances are constantly accompanied by depression and anxiety in AS, but their interrelations are poorly understood. This study was designed to evaluate sleep disturbances and their association with demographic variables, pain, disease-specific variables, functional status, covering depression and anxiety in AS patients.

Methods

The 314 patients with AS and age- and sex-matched controls took part in the study, completed a battery of questionnaires, and participated in long-term follow-up. Blood samples were taken to measure C-reactive protein (CRP) and the erythrocyte sedimentation rate (ESR). The association among sleep, pain, disease activity, functional status, depression, and anxiety were assessed by using Pearson/Spearman correlations and multiple regression analysis.

Results

The Pittsburgh Sleep Quality Index (PSQI) score of the Chinese version was significantly higher in the AS group than in the control group (P = 0.020). Of the 314 patients with AS, 184 (58.6%) had a high risk for sleep disturbances. The PSQI score was associated with age, years of education, ESR, CRP, overall assessment of health, pain, morning stiffness, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), depression, and anxiety (all P < 0.001), but were not associated with disease duration, fingertip-to-floor distance, and Bath Ankylosing Spondylitis Metrology Index (BASMI) (P > 0.05). In hierarchic multiple regression analysis, the medical and psychological variables contributed significantly to the variance in sleep-disturbances scores, adding an additional 23.9% to the overall R² beyond that accounted for by demographic variables (R-square, 8.5%), resulting in a final R²of 42.6%. Multiple stepwise regression analysis revealed that anxiety was the maximal statistical contribution in predicting sleep disturbances (standardized coefficients, 0.287).

Conclusions

The prevalence of sleep disturbances in AS patients is higher than it is generally thought to be. Depression, anxiety, nocturnal pain, and total back pain are the major contributors of sleep disturbances in AS.

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.

Sodium oxybate for the treatment of fibromyalgia

INTRODUCTION

Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid that is synthesized within the CNS, mostly from its parent compound gamma amino butyric acid (GABA). GHB acts as a neuromodulator/neurotransmitter to affect neuronal activity of other neurotransmitters and so, stimulate the release of growth hormone. Its sodium salt (sodium oxybate: SXB) was approved by the Food and Drug Administration (FDA) for the treatment of narcolepsy. SXB has shown to improve disrupted sleep and increase NR3 (slow-wave restorative) sleep in patients with narcolepsy. It is rapidly absorbed and has a plasma half-life of 30 - 60 min, necessitating twice-nightly dosing. Most of the observed effects of SXB result from binding to GABA-B receptors.

AREAS COVERED

Several randomized, controlled trials demonstrated significantly improved fibromyalgia (FM) symptoms with SXB. As seen in narcolepsy trials, SXB improved sleep of FM patients, increased slow-wave sleep duration as well as delta power, and reduced frequent night-time awakenings. Furthermore, FM pain and fatigue was consistently reduced with nightly SXB over time. Commonly reported adverse events included headache, nausea, dizziness and somnolence. Despite its proven efficacy, SXB did not receive FDA approval for the management of FM in 2010, mostly because of concerns about abuse.

EXPERT OPINION

Insomnia, fatigue and pain are important clinical FM symptoms that showed moderate improvements with SXB in several large, well-designed clinical trials. Because of the limited efficacy of currently available FM drugs additional treatment options are needed. In particular, drugs like SXB - which belong to a different drug class than other Food and Drug Administration (FDA)-approved FM medications such as pregabalin, duloxetine and milnacipran - would provide a much-needed addition to presently available treatment options. However, the FDA has set the bar high for future SXB re-submissions, with requirements of superior efficacy and improved risk mitigation strategies. At this time, no future FDA submission of SXB for the fibromyalgia indication is planned.

Spatial and reversal learning in the Morris water maze are largely resistant to six hours of REM sleep deprivation following training

This first test of the role of REM (rapid eye movement) sleep in reversal spatial learning is also the first attempt to replicate a much cited pair of papers reporting that REM sleep deprivation impairs the consolidation of initial spatial learning in the Morris water maze. We hypothesized that REM sleep deprivation following training would impair both hippocampus-dependent spatial learning and learning a new target location within a familiar environment: reversal learning. A 6-d protocol was divided into the initial spatial learning phase (3.5 d) immediately followed by the reversal phase (2.5 d). During the 6 h following four or 12 training trials/day of initial or reversal learning phases, REM sleep was eliminated and non-REM sleep left intact using the multiple inverted flowerpot method. Contrary to our hypotheses, REM sleep deprivation during four or 12 trials/day of initial spatial or reversal learning did not affect training performance. However, some probe trial measures indicated REM sleep-deprivation-associated impairment in initial spatial learning with four trials/day and enhancement of subsequent reversal learning. In naive animals, REM sleep deprivation during normal initial spatial learning was followed by a lack of preference for the subsequent reversal platform location during the probe. Our findings contradict reports that REM sleep is essential for spatial learning in the Morris water maze and newly reveal that short periods of REM sleep deprivation do not impair concurrent reversal learning. Effects on subsequent reversal learning are consistent with the idea that REM sleep serves the consolidation of incompletely learned items.

The use of a non-benzodiazepine hypnotic sleep-aid (Zolpidem) in patients undergoing ACL reconstruction: a randomized controlled clinical trial

PURPOSE

Previous studies have addressed post-operative pain management after ACL reconstruction by examining the use of intra-articular analgesia and/or modification of anesthesia techniques. To our knowledge, however, no previous studies have evaluated the effect of zolpidem on post-operative narcotic requirements, pain, and fatigue in patients undergoing outpatient arthroscopic ACL reconstruction. The purpose of this prospective, blinded, randomized, controlled clinical study was to evaluate the effect of zolpidem on post-operative narcotic requirements, pain, and fatigue in patients undergoing outpatient arthroscopic ACL reconstruction.

METHODS

Twenty-nine patients undergoing arthroscopic ACL reconstruction were randomized to a treatment group or placebo group. Both groups received post-operative hydrocodone/acetaminophen bitartrate (Vicodin ES). Patients in the treatment group received a single dose of zolpidem for the first seven post-operative nights. Patients in the placebo group received a gelatin capsule similar in appearance to zolpidem. The amount of Vicodin used in each group, the amount of post-operative pain, and the amount of post-operative fatigue were analyzed.

RESULTS

Following ACL reconstruction, a 28% reduction was seen in the total amount of narcotic consumed with zolpidem (P = 0.047) when compared to placebo. There were no significant differences in post-operative pain or fatigue levels between zolpidem and placebo.

CONCLUSION

Adding zolpidem to the post-operative medication regimen after arthroscopic ACL reconstruction helps to lower the amount of narcotic pain medication required for adequate analgesia.

LEVEL OF EVIDENCE

Randomized controlled clinical trial, Level I.

Intrathecal administration of antioxidants attenuates mechanical pain hypersensitivity induced by REM sleep deprivation in the rat

Background Sleep deprivation as well as peripheral neuropathy and cutaneous neurogenic inflammation has a facilitatory effect on pain perception. Here we studied whether oxidative stress-related mechanisms in the spinal cord that have been shown to contribute to pain facilitation in peripheral neuropathy and cutaneous neurogenic inflammation play a role in sleep deprivation-induced pain hypersensitivity Methods Flower pot method was used to induce rapid eye movement sleep deprivation (REMSD) of 48 h duration in the rat that had a chronic intrathecal (i.t.) catheter for spinal administration of drugs. Pain behavior was assessed by determining the monofilament-induced limb withdrawal response. Results REMSD of 48 h produced mechanical hypersensitivity that was attenuated in a dose-related fashion by i.t. administration of two different antioxidants, phenyl-N-tert-butylnitrone (PBN) or 4-hydroxy-2,2,6,6-tetramethylpiperidine-1 oxyl (TEMPOL). While both antioxidants attenuated mechanical pain behavior also in control animals, their effects were significantly stronger after REMSD than in control conditions. Conversely, i.t. administration of a reactive oxygen species (ROS) donor, tert-butylhydroperoxide (t-BOOH), in control animals produced pain hypersensitivity that was prevented by i.t. pretreatment with an antioxidant, TEMPOL. I.t. treatment with PBN or TEMPOL at the currently used doses failed to influence motor behavior in the Rotarod test. Conclusions The results indicate that among common mechanisms contributing to mechanical pain hypersensitivity following sleep deprivation as well as nerve injury or neurogenic inflammation is oxidative stress in the spinal cord. Implications Compounds with antioxidant properties might prove useful in suppressing the vicious pronociceptive interaction between chronic pain and sleep-deprivation.