REM sleep deprivation decreases the antinociceptive property of enkephalinase-inhibition, morphine and cold-water-swim

Impact of physical therapy techniques and common interventions on sleep quality in patients with chronic pain: A systematic review

This systematic review aims to find effectful healthcare strategies, with special focus on drug-free interventions and physical therapy, as part of the treatment for sleep in patients with chronic musculoskeletal pain. Data search was conducted across seven scientific databases. This review is deposited in the Prospero International prospective register of systematic reviews (CRD42023452574). Seventeen RCTs from different healthcare fields complied with our inclusion criteria. Two RCTs investigated manual therapy, five RCTs therapeutic exercise, one RCT Fu's subcutaneous needling, two RCTs physical agents (one on balneotherapy and one on cryo-stimulation), two RCTs cognitive-behavioral therapy, and four RCTs pharmacological therapy and their effect on sleep quality and/or quantity in patients suffering from chronic pain. We included the four RCT's in this systematic review with the purpose to be able to compare natural interventions with allopathic ones. As allopathic interventions are more prone to have secondary negative effects than physical therapy, compare the two types of interventions could be in favor of choosing the most effective treatment with the least secondary negative effects. Additionally, two RCTs on neurofeedback and limbic neuromodulation were also included. The results of the included studies suggest that strategies such as manual therapy, therapeutic exercise, Fu's subcutaneous needling, balneotherapy, cryo-stimulation, neurofeedback, limbic neuromodulation, cognitive-behavioral therapy, and pharmacological therapies have positive effects on patients suffering from chronic pain and sleep disturbances, especially when they suffer musculoskeletal pain. Secondary negative effects were found for the possible overuse of certain medicines such as morphine, a huge problem in the United States. Sleep deficiency is an independent risk factor for many diseases, including chronic pain syndrome and therefore more studies are needed to find non-toxic interventions for people suffering sleep disorders associated with systemic diseases and pain.

Modeling homeostatic and circadian modulation of human pain sensitivity

Introduction

Mathematical modeling has played a significant role in understanding how homeostatic sleep pressure and the circadian rhythm interact to influence sleep-wake behavior. Pain sensitivity is also affected by these processes, and recent experimental results have measured the circadian and homeostatic components of the 24 h rhythm of thermal pain sensitivity in humans. To analyze how rhythms in pain sensitivity are affected by disruptions in sleep behavior and shifts in circadian rhythms, we introduce a dynamic mathematical model for circadian and homeostatic regulation of sleep-wake states and pain intensity.

Methods

The model consists of a biophysically based, sleep-wake regulation network model coupled to data-driven functions for the circadian and homeostatic modulation of pain sensitivity. This coupled sleep-wake-pain sensitivity model is validated by comparison to thermal pain intensities in adult humans measured across a 34 h sleep deprivation protocol.

Results

We use the model to predict dysregulation of pain sensitivity rhythms across different scenarios of sleep deprivation and circadian rhythm shifts, including entrainment to new environmental light and activity timing as occurs with jet lag and chronic sleep restriction. Model results show that increases in pain sensitivity occur under conditions of increased homeostatic sleep drive with nonlinear modulation by the circadian rhythm, leading to unexpected decreased pain sensitivity in some scenarios.

Discussion

This model provides a useful tool for pain management by predicting alterations in pain sensitivity due to varying or disrupted sleep schedules.

Effect of sleep loss on pain-New conceptual and mechanistic avenues

Introduction

Sleep disturbances increase pain sensitivity in clinical and preclinical settings, but the precise mechanisms are unknown. This represents a major public health issue because of the growing sleep deficiency epidemic fueled by modern lifestyle. To understand the neural pathways at the intersection between sleep and pain processes, it is critical to determine the precise nature of the sleep disruptions that increase pain and the specific component of the pain response that is targeted.

Methods

We performed a review of the literature about sleep disturbances and pain sensitivity in humans and rodents by taking into consideration the targeted sleep stage (REMS, non-NREMS, or both), the amount of sleep lost, and the different types of sleep disruptions (partial or total sleep loss, duration, sleep fragmentation or interruptions), and how these differences might affect distinct components of the pain response.

Results

We find that the effects of sleep disturbances on pain are highly conserved among species. The major driver for pain hypersensitivity appears to be the total amount of sleep lost, while REMS loss by itself does not seem to have a direct effect on pain sensitivity. Sleep loss caused by extended wakefulness preferentially increases pain perception, whereas interrupted and limited sleep strongly dysregulates descending controls such as DNIC, especially in women.

Discussion

We discuss the possible mechanisms involved, including an increase in inflammatory processes, a loss of nociceptive inhibitory pathways, and a defect in the cognitive processing of noxious input.

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.

Association between sleep disturbance and low back and pelvic pain in 4-month postpartum women: A cross-sectional study

PURPOSE

Persistent low back and pelvic pain (LBPP) is a postpartum-specific health problem. Sleep disturbances' association with persistent LBPP is not yet clear. We aimed to examine the cross-sectional association between sleep disturbance and persistent LBPP at 4 months postpartum.

METHODS

We enrolled 120 women with LBPP during pregnancy (mean age, 31.8; standard deviation, 4.9 years). The primary outcome was persistent LBPP. We assessed LBPP severity at 4 months postpartum using the Numerical Rating Scale (NRS), where women with an NRS score of ≥ 4 at 4 months postpartum were allocated to the persistent LBPP group. We assessed sleep disturbance at 4 months postpartum using the Japanese version of the Pittsburgh Sleep Quality Index with a total score of ≥ 6 indicating sleep disturbance. Moreover, we performed univariate and multiple logistic regression analyses to examine the cross-sectional association of sleep disturbance with persistent LBPP. The relevant confounding variables were age, body mass index, parity, and history of LBPP before pregnancy.

RESULTS

Among the 120 women, 45 women had persistent LBPP (37.5%) with 32 (71.1%) of them reporting sleep disturbance. There was a significant association of sleep disturbance with persistent LBPP (odds ratio [OR], 2.81; 95% confidence interval [95% CI], 1.28-6.19), which remained after adjustments for confounding variables (OR, 2.98; 95% CI, 1.31-6.75).

CONCLUSION

Our findings indicate that sleep disturbance is associated with persistent LBPP at 4 months postpartum; therefore, it should be taken into consideration in postpartum women with persistent LBPP.

Sex Differences, Sleep Disturbance and Risk of Persistent Pain Associated With Groin Hernia Surgery: A Nationwide Register-Based Cohort Study

Persistent pain after groin hernia repair is a major health problem. Sleep disturbance is associated with heightened pain sensitivity. The main objective of this study was to examine the role of sleep disturbance in the development and long-term maintenance of chronic postherniorrhaphy inguinal pain (CPIP), with exploration of sex differences. From 2012 to 2017, a national cohort of patients with prior groin hernia repair (n = 2084;45.8% females) were assessed for the development of CPIP 12 months after surgery. Patients then underwent long-term (median 5.0 years) follow-up to evaluate the contribution of sex and sleep disturbance on the maintenance of CPIP. Associations between pre- and postoperative sleep problems (assessed at long-term follow-up) and CPIP were tested using logistic regression. Females had higher rates of CPIP with negative impact on daily activities 12 months after surgery as compared to males (14.6 vs 9.2%, P < .0005), and were more likely to have moderate-severe CPIP in the long-term (3.1 vs 1.2%, P = .003). Preoperative sleep problems predicted development of CPIP 12 months after surgery (adjusted odds ratio [aOR] 1.76 [95%CI 1.26-2.46], P = .001) and CPIP in the long-term (aOR 2.20 [1.61-3.00] , P < .0001). CPIP was associated with insomnia and depression. Sleep disturbance may increase the risk for CPIP, and contribute to maintenance of postsurgical pain. PERSPECTIVE: Females are at heightened risk for CPIP as compared to males. Increased severity of pain symptoms are linked to poorer sleep and psychiatric morbidity. Given the robust associations between sleep disturbance and CPIP, interventions which consolidate and promote sleep, especially in females, may improve long-term pain control.

Preoperative sleep quality and adverse pain outcomes after total hip arthroplasty

BACKGROUND

Sleep disturbance is thought to aggravate acute postoperative pain. The influence of preoperative sleep problems on pain control in the long-term and development of chronic postsurgical pain is largely unknown.

METHODS

This prospective, observational study aimed to examine the links between preoperative sleep disturbance (Pittsburgh Sleep Quality Index, PSQI) and pain severity (Brief Pain Inventory, BPI) 6 months postoperative (primary outcome), objective measures of pain and postoperative pain control variables (secondary outcomes). Patients (n = 52) with disabling osteoarthritis (OA) pain undergoing total hip arthroplasty (THA) were included. Quantitative sensory testing (QST) was performed preoperatively on the day of surgery to evaluate pain objectively. Clinical data, as well as measures of sleep quality and pain, were obtained preoperatively and longitudinally over a 6-month period.

RESULTS

Preoperatively, sleep disturbance (i.e., PSQI score >5) occurred in 73.1% (n = 38) of THA patients, and pain severity was high (BPI pain severity 5.4 ± 1.3). Regression models, adjusting for relevant covariates, showed that preoperative PSQI score predicted pain severity 6 months postoperative (β = 0.091 (95% CI 0.001-0.181), p = .048, R²  = 0.35). Poor sleep quality was associated with increased pressure pain sensitivity and impaired endogenous pain inhibitory capacity (R² range 0.14-0.33, all p's < 0.04). Moreover, preoperative sleep disturbance predicted increased opioid treatment during the first 24 hr after surgery (unadjusted β = 0.009 (95% CI 0.002-0.015) mg/kg, p = .007, R²  = 0.15).

CONCLUSIONS

Preoperative sleep disturbance is prevalent in THA patients, is associated with objective measures of pain severity, and independently predicts immediate postoperative opioid treatment and poorer long-term pain control in patients who have undergone THA.

SIGNIFICANCE

Poor sleep quality and impaired sleep continuity are associated with heightened pain sensitivity, but previous work has not evaluated whether preoperative sleep problems impact long-term postoperative pain outcomes. Here, we show that sleep difficulties prior to total hip arthroplasty adversely predict postoperative pain control 6 months after surgery. Given sleep difficulties robustly predict pain outcomes, targeting and improving sleep may have salutary effects on postoperative pain reports and management.

Intermittent REM sleep deprivation attenuates the development of morphine tolerance and dependence in male rats

Opioid agonists are used in clinic for pain management, however this application is challenged by development of tolerance and dependence following prolonged exposure. Various approaches have been suggested to address this concern, however, there is still no consensus among the researchers. Neural processing of sleep and nociception are co-regulated through shared brain regions having bidirectional interplays. Thus, we aimed to investigate whether application of REM sleep deprivation (REM-SD) could affect morphine analgesic tolerance and dependence. To this end, adult male rats underwent sleep deprivation during light and dark phases (LSD and DSD, respectively) using the inverted flower pot method and then tolerance and dependence was induced by repeated injection of morphine for 7 days (10 mg/kg, daily, i.p.). Results indicated that REM-SD delays the development of tolerance to morphine during both phases; however this effect was more potent following LSD. Moreover, LSD decreased the baseline thermal threshold and total withdrawal score. One possible hypothesis for our observations is REM-SD-induced attenuation of orexin system which is still controversial among the researchers. Other stronger possibilities might be down-regulation of opioid receptors in response to sleep loss experience. Finally, it seems that modification of sleep periods may assist to decrease the severity of opioid tolerance and dependence.

The Role of Sleep in the Transition from Acute to Chronic Musculoskeletal Pain in Youth-A Narrative Review

Musculoskeletal pain is common in the general pediatric population and is a challenge to youth, their parents, and society. The majority of children experiencing musculoskeletal pain will recover; however, a small subgroup of youth develops chronic pain. There is limited understanding of the factors that affect the transition from acute to chronic pain in youth. This review introduces sleep deficiency in the acute to chronic pain transition, exploring the potential mediational or mechanistic role and pathways of sleep in this process, including the interaction with sensory, psychological, and social components of pain and highlighting new avenues for treatment. Biological mechanisms include the increased production of inflammatory mediators and the effect on the hypothalamus-pituitary-adrenal (HPA) axis and on the dopaminergic signaling. Psychological and social components include the effect of sleep on the emotional-affective and behavioral components of pain, the negative impact on daily and social activities and coping strategies and on the reward system, increased pain catastrophizing, fear of pain, pain-related anxiety, hypervigilance, and social isolation. Future longitudinal studies are needed to elucidate these mechanistic pathways of the effect of sleep on the transition from acute to chronic pain, which may lead to the development of new treatment targets to prevent this transition.

Experimental sleep disruption attenuates morphine analgesia: findings from a randomized trial and implications for the opioid abuse epidemic

Preclinical studies demonstrate that sleep disruption diminishes morphine analgesia and modulates reward processing. We sought to translate these preclinical findings to humans by examining whether sleep disruption alters morphine's analgesic and hedonic properties. We randomized 100 healthy adults to receive morphine versus placebo after two nights of undisturbed sleep (US) and two nights of forced awakening (FA) sleep disruption. Sleep conditions were counterbalanced, separated by a two-week washout. The morning after both sleep conditions, we tested cold pressor pain tolerance before and 40-min after double-blind injection of .08 mg/kg morphine or placebo. The primary outcome was the analgesia index, calculated as the change in cold pressor hand withdrawal latency (HWL) before and after drug injection. Secondary outcomes were ratings of feeling "high," drug "liking," and negative drug effects. We found a significant sleep condition by drug interaction on the analgesia index (95% CI - 0.57, - 0.001). After US, subjects receiving morphine demonstrated significantly longer HWL compared to placebo (95% CI 0.23, 0.65), but not after FA (95% CI - 0.05, 0.38). Morphine analgesia was diminished threefold under FA, relative to US. After FA, females (95% CI - 0.88, - 0.05), but not males (95% CI - 0.23, 0.72), reported decreased subjective "high" effects compared to US. After FA, females (95% CI 0.05, 0.27), but not males (95% CI - 0.10, 0.11), administered morphine reported increased negative drug effects compared to US. These data demonstrate that sleep disruption attenuates morphine analgesia in humans and suggest that sleep disturbed males may be at greatest risk for problematic opioid use.

The effects of recovery sleep on pain perception: A systematic review

Experimental studies highlight profound effects of sleep disruptions on pain, showing that sleep deprivation (SD) leads to hyperalgesic pain changes. On the other hand, given that sleep helps normalizing bodily functions, a crucial role of restorative sleep in the overnight restoration of the pain system seems likely. Thus, a systematic review of experimental studies on effects of recovery sleep (RS; subsequently to SD) on pain was performed with the aim to check whether RS resets hyperalgesic pain changes occurring due to SD. Empirical animal and human studies including SD-paradigms, RS and pain assessments were searched in three databases (PubMed, Web of Science, PsycINFO) using a predefined algorithm. 29 studies were included in this review. Most results indicated a reset of enhanced pain sensitivity and vulnerability following RS, especially when total SD was implemented and pressure pain or painful symptoms (human studies) were assessed. Further research should focus on whether and how recovery is altered in chronic pain patients, as this yields implications for pain treatment by enhancing or stabilizing RS.

Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications

Pain can be both a cause and a consequence of sleep deficiency. This bidirectional relationship between sleep and pain has important implications for clinical management of patients, but also for chronic pain prevention and public health more broadly. The review that follows will provide an overview of the neurobiological evidence of mechanisms thought to be involved in the modulation of pain by sleep deficiency, including the opioid, monoaminergic, orexinergic, immune, melatonin, and endocannabinoid systems; the hypothalamus-pituitary-adrenal axis; and adenosine and nitric oxide signaling. In addition, it will provide a broad overview of pharmacological and non-pharmacological approaches for the management of chronic pain comorbid with sleep disturbances and for the management of postoperative pain, as well as discuss the effects of sleep-disturbing medications on pain amplification.

I'm tired and it hurts! Sleep quality and acute pain response in a chronic pain population

OBJECTIVE/BACKGROUND

There are bidirectional links between sleep quality and pain, with recent research suggesting that sleep impairment more strongly predicts future pain than vice versa. Relatively few studies have examined the relationship between sleep quality and acute pain among chronic pain patients. The purpose of the current study is to investigate relationships among subjective sleep quality and behavioral and physiological responses to a cold pressor pain task (CPT) in chronic pain patients.

PATIENTS/METHODS

In sum, 120 individuals with chronic pain were included. Participants completed a series of questionnaires followed by the CPT. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Physiological baseline state and stress response were assessed before and during the CPT using heart rate (HR), electromyography frontalis (EMGF), galvanic skin response conductance (GSR), and skin temperature (°C). Multiple linear regressions adjusting for opioid usage were performed.

RESULTS

After adjusting for opioid use, PSQI global score explained significant variance in pain tolerance (B = -5.37, β = -0.23, p = 0.01), baseline GSR (B = -0.66, β = -0.24, p = 0.01), and HR change from baseline to CPT (B = 1.33, β = 0.25, p = 0.01).

CONCLUSIONS

Worse perceived sleep quality was associated with lower pain tolerance, lower baseline GSR conductance, and greater HR change from baseline to CPT. These findings underscore the importance of accounting for opioid usage and psychological dimensions of pain in the relationship between sleep and acute pain response in chronic pain populations.

PER3 variable number tandem repeat (VNTR) polymorphism modulates the circadian variation of the descending pain modulatory system in healthy subjects

We evaluated the circadian pattern of variation of the descending pain modulatory system (DPMS) using a conditioned pain modulation (CPM) paradigm according to the variable-number tandem-repeat (VNTR) of the clock gene PER3 polymorphism. We assessed the relationship between the genotypes PER3^4/4 and PER3^5/5 and the temporal pattern of variation across the day using the following measures: the heat pain threshold (HPT), the cold pressure test (CPT), and the serum levels of BDNF and S100-B protein. The ∆-values (from afternoon to morning) of these measures were used for the analysis. The circadian phenotype was according to the mid-point sleep time established by the Munich ChronoType Questionnaire (MCTQ). We included 18 healthy volunteers (15 women) ages 18 to 30. A Generalized Linear Model (GLM) revealed a significant difference in the ∆-CPM-task between Per3^4/4 and Per3^5/5 genotypes, with means (SDs) of -0.41 (0.78) vs. 0.67 (0.90) (χ² = 7.256; df = 1' P = 0.007), respectively. Both sleep deprivation of at least 2 h/day (B = -0.96, 95% confidence interval (CI) = -1.86 to -0.11)) and the ∆-S100-B protein (-0.03, 95% CI = -0.06 to -0.02) were negatively correlated with the ∆-CPM-task, while the ∆-BDNF was positively correlated with the ∆-CPM-task (0.015, 95% CI = 0.01 to 0.03). We observed a difference in the ∆-CPT between PER3^4/4 and PER3^5/5 (0.11 (4.51) vs. 4.00 (2.60), respectively) (χ² = 22.251; df = 1 P = 0.001). These findings suggest that the polymorphism of PER3^5/5 is associated with a decrease in the inhibitory function of the DPMS over the course of the day. However, sleep deprivation is an independent factor that also reduces the inhibitory function of the DPMS, regardless of the PER3 VNTR polymorphism.

The influence of rapid eye movement sleep deprivation on nociceptive transmission and the duration of facial allodynia in rats: a behavioral and Fos immunohistochemical study

Background

Disrupted sleep is associated with a reciprocal influence on headaches and is one of the contributing factors in the process of chronicity. The goal of the present study was to investigate the influence of sleep on headaches using animal rapid eye movement (REM) sleep deprivation and supradural capsaicin infusion models.

Method

Sprague-Dawley rats underwent REM sleep deprivation (REMSD) for 96 h. The sensory threshold to mechanical stimuli, assessed by the von Frey monofilament test, was measured during the REMSD period. Additionally, the Fos protein expression level was measured in the trigeminocervical complex, periaqueductal gray, and hypothalamus. Following supradural infusion of capsaicin, we evaluated the duration of facial allodynia for 28 days after REMSD.

Results

After REMSD, the sensory threshold to mechanical stimuli was significantly decreased (p < 0.01) and Fos-positivity in the posterior (p = 0.010) and dorsomedial hypothalamus (p = 0.024), ventrolateral periaqueductal gray (p = 0.016), and superficial layer of the trigeminocervical complex (p = 0.019) were significantly increased. The duration of facial allodynia induced by supradural capsaicin infusion was significantly longer in the REM sleep deprivation and capsaicin infusion group (Day 10 PSD vs. Day 25 PSD).

Conclusion

The present study demonstrates that REM sleep deprivation increased nociceptive transmission from trigeminal nerve endings. Furthermore, it suggests that sleep deprivation may contribute to the chronicity of facial allodynia.

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.

Total Sleep Deprivation and Pain Perception during Cold Noxious Stimuli in Humans

BACKGROUND AND AIMS

A substantial portion of the population suffers from chronic pain leading to significant health care costs and lost productivity. Loss of sleep duration and quality are widely reported in patients suffering from a variety of acute or chronic pain conditions. Conversely, sleep loss has been known to elevate pain perception; thus a potential bi-directional relationship exists between sleep deprivation and pain. To date, the majority of studies examining the relationship between experimentally induced pain and sleep loss have focused on the measurement of pain threshold. Additionally, despite evidence of sex differences in ratings of perceived pain, previous studies examining pain following sleep loss have not probed for sex differences. We examined the effects of 24-hour total sleep deprivation (TSD) on perceived pain during a 2-minute cold pressor test (CPT). We hypothesized that TSD would augment perceived pain and that women would demonstrate an elevated pain response compared to men.

METHODS

Testing was carried out in 14 men and 13 women. All subjects reported to be nonsmokers with no history of cardiovascular disease, autonomic dysfunction, asthma, or diabetes. All female subjects were free of oral contraceptive use, and were tested during the early follicular phase of the menstrual cycle. Trial order was randomized and testing sessions (Normal sleep (NS) and TSD) were separated by approximately one month. Subjects immersed their left hand, up to the wrist, in an ice water bath (~1°C), and perceived pain was recorded every 15 seconds from a modified Borg scale (6-20 arbitrary units a.u.).

RESULTS

Perceived pain responses during CPT were augmented following TSD (Δ1.2 a.u.; time × condition, p<0.05). The augmented pain response following TSD was noted when perceived pain was expressed as mean (NS Δ7.0±0.5 vs. TSD Δ8.2±0.5 a.u.; p<0.05) or peak (NS Δ8.9±0.6 vs. TSD Δ10.2±0.5 a.u.; p<0.05) perceived pain. The effects of TSD on perceived pain were similar in both men and women (condition × time × sex, p>0.05).

CONCLUSIONS AND IMPLICATIONS

We conclude that TSD significantly augments perceived pain during CPT, but this response was not sex dependent. These findings support emerging evidence that adequate sleep represents a relevant, and cost effective, preventative/therapeutic strategy to reduce self-perceived pain in both men and women.

Vitamin D and Pain: Vitamin D and Its Role in the Aetiology and Maintenance of Chronic Pain States and Associated Comorbidities

The emergence of new data suggests that the benefits of Vitamin D extend beyond healthy bones. This paper looks at Vitamin D and its role in the aetiology and maintenance of chronic pain states and associated comorbidities. The interfaces between pain and Vitamin D and the mechanisms of action of Vitamin D on pain processes are explored. Finally the association between Vitamin D and pain comorbidities such as sleep and depression is investigated. The paper shows that Vitamin D exerts anatomic, hormonal, neurological, and immunological influences on pain manifestation, thereby playing a role in the aetiology and maintenance of chronic pain states and associated comorbidities. More research is necessary to determine whether Vitamin D is useful in the treatment of various pain conditions and whether or not the effect is limited to patients who are deficient in Vitamin D.

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.

The association of sleep and pain: an update and a path forward

Ample evidence suggests that sleep and pain are related. However, many questions remain about the direction of causality in their association, as well as mechanisms that may account for their association. The prevailing view has generally been that they are reciprocally related. The present review critically examines the recent prospective and experimental literature (2005-present) in an attempt to update the field on emergent themes pertaining to the directionality and mechanisms of the association of sleep and pain. A key trend emerging from population-based longitudinal studies is that sleep impairments reliably predict new incidents and exacerbations of chronic pain. Microlongitudinal studies employing deep subjective and objective assessments of pain and sleep support the notion that sleep impairments are a stronger, more reliable predictor of pain than pain is of sleep impairments. Recent experimental studies suggest that sleep disturbance may impair key processes that contribute to the development and maintenance of chronic pain, including endogenous pain inhibition and joint pain. Several biopsychosocial targets for future mechanistic research on sleep and pain are discussed, including dopamine and opioid systems, positive and negative affect, and sociodemographic factors.

PERSPECTIVE

This critical review examines the recent prospective and experimental research (2005-present) on the association of sleep and pain in an attempt to identify trends suggestive of directionality and potential mechanisms. An update on this literature is needed to guide future clinical efforts to develop and augment treatments for chronic sleep disturbance and chronic pain.

individual variation in sleep quality and duration is related to cerebral mu opioid receptor binding potential during tonic laboratory pain in healthy subjects

OBJECTIVE

Although poor sleep is a consequence of pain, sleep disturbance reciprocally induces hyperalgesia and exacerbates clinical pain. Conceptual models of chronic pain implicate dysfunctional supraspinal pain processing mechanisms, mediated in part by endogenous opioid peptides. Our preliminary work indicates that sleep disruption impairs psychophysical measures of descending pain modulation, but few studies have investigated whether insufficient sleep may be associated with alterations in endogenous opioid systems. This preliminary, exploratory investigation sought to examine the relationship between sleep and functioning of the cerebral mu opioid system during the experience of pain in healthy participants.

SUBJECTS AND DESIGN

Twelve healthy volunteers participated in a 90-minute positron emission tomography imaging scan using [11C]Carfentanil, a mu opioid receptors agonist. During the session, pain responses to a 10% topical capsaicin cream were continuously rated on a 0-100 scale. Participants also completed the Pittsburgh Sleep Quality Index (PSQI).

RESULTS

Poor sleep quality (PSQI) was positively and significantly associated with greater binding potential (BP) in regions within the frontal lobes. In addition, sleep duration was negatively associated with BP in these areas as well as the temporal lobe and anterior cingulate.

CONCLUSIONS

These findings suggest that poor sleep quality and short sleep duration are associated with endogenous opioid activity in these brain regions during the application of a noxious stimulus. Elucidating the role of the endogenous opioid system in mediating some of the associations between sleep and pain could significantly improve our understanding of the pathophysiology of chronic pain and might advance clinical practice by suggesting interventions that could buffer the adverse effects of poor sleep on pain.

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.

The comorbidity of insomnia, chronic pain, and depression: dopamine as a putative mechanism

Epidemiological, cross-sectional, and prospective studies suggest that insomnia, chronic pain, and depression frequently co-occur and are mutually interacting conditions. However, the mechanisms underlying these comorbid disorders have yet to be elucidated. Overlapping mechanisms in the central nervous system suggest a common neurobiological substrate(s) may underlie the development and interplay of these disorders. We propose that the mesolimbic dopamine system is an underappreciated and attractive venue for the examination of neurobiological processes involved in the interactions, development, exacerbation, and maintenance of this symptom complex. In the present article, studies from multiple disciplines are reviewed to highlight the role of altered dopaminergic function in the promotion of arousal, pain sensitivity, and mood disturbance. We argue that studies aiming to elucidate common factors accounting for the comorbidity of insomnia, chronic pain, and depression should evaluate functioning within the mesolimbic dopaminergic system and its effect on common processes known to be dysregulated in all three disorders.

Differences in suprathreshold heat pain responses and self-reported sleep quality between patients with temporomandibular joint disorder and healthy controls

The purpose of this study was to examine differences in heat pain threshold (HPTh) and heat pain tolerance (HPTo) between temporomandibular joint disorder (TMJD) patients and healthy controls. Using suprathreshold heat pain, this study also examined between-group (i.e. TMJD vs. healthy controls) differences in hyperalgesia and temporal summation (TS) of heat pain. Lastly, whether between-group differences in these heat pain outcomes were mediated by self-reported sleep quality was also tested. A total of 119 participants (41% TMJD) completed the current study. HPTh and HPTo responses were assessed at the ventral forearm with an ascending method of limits, while hyperalgesia and TS responses were assessed at the dorsal forearm at temperatures of 46, 48 and 50 °C. Prior to completion of heat pain procedures, participants completed the Pittsburgh Sleep Quality Index. Significant between-group differences in HPTh and HPTo were not observed. TMJD patients demonstrated significantly greater hyperalgesia than healthy controls at 46 °C only, but there were no differences for TS. Furthermore, TMJD patients reported significantly poorer sleep quality compared with healthy controls. Data analysis revealed a significant simple mediation effect whereby the presence of TMJD was strongly associated with poorer self-reported sleep quality, which, in turn, was related to enhanced hyperalgesia at 46 °C. These findings support the hypothesis that the thermal hyperalgesia demonstrated by TMJD patients may be related to poor quality of their self-reported sleep. The ability of interventions that improve sleep quality to also affect pain sensitivity is currently the topic of ongoing investigation.

Pain tolerance and obstructive sleep apnea in the elderly

OBJECTIVE

Patients with painful conditions often suffer from sleep disturbances. However, changes in sleep pattern per se could also influence pain tolerance. Untreated obstructive sleep apnea (OSA) causes major disturbances in sleep pattern. The aim of this study was to assess whether continuous positive airway pressure (CPAP) treatment in elderly patients with OSA would result in improved pain tolerance.

DESIGN

Randomized, double-blind crossover study.

SETTING

Geriatric sleep center based in Antoine Charial University Hospital (Lyon, France).

PARTICIPANTS

A total of 13 consecutive OSA patients aged 70 and older randomly assigned CPAP treatment (lowCPAP versus highCPAP). Eleven patients completed the study.

MEASUREMENTS

Overnight sleep recording, electrical pain tolerance assessment, and visual analog scale for sleep quality were performed.

RESULTS

Both low- and highCPAP treatment significantly improved respiratory parameters. However, compared with baseline, the electrical pain tolerance score was significantly enhanced (analgesic effect) only under highCPAP treatment (21.2 ± 10.9 versus 28.4 ± 16.0; P = .03).

CONCLUSION

The treatment of OSA with CPAP would have an analgesic effect. This would represent a unique outcome attributed to CPAP treatment. Given the high prevalence of both OSA and chronic pain conditions in the elderly; our findings could hold many implications for very large segments of the elderly population.

Mechanisms by which sleep disturbance contributes to osteoarthritis pain: a conceptual model

Sleep disturbance is prevalent in aging and painful rheumatologic populations, but it has largely been a neglected dimension of the routine clinical care of arthritis patients. Pain associated with osteoarthritis (OA) is a leading cause of disability worldwide, and factors that contribute to pain in OA are poorly understood. Sleep disturbance is not only a consequence of pain, it is also likely to play an integral role in pain expression. Emerging research suggests that many patients with OA demonstrate signs of generalized hyperalgesia and faulty central pain modulatory processing similar to other idiopathic pain disorders, such as fibromyalgia. Sleep disruption is increasingly recognized as a direct contributor to both hyperalgesia and impaired endogenous pain modulation. This article reviews the extant literature on sleep disturbance and hyperalgesia in patients with OA. We propose a conceptual working model describing pathways by which sleep disturbance interacts directly with central pain processing mechanisms and inflammatory processes, and indirectly with mood and physical functioning to augment clinical OA pain. The clinical and research implications of the model are discussed.

Stress-induced analgesia

For over 30 years, scientists have been investigating the phenomenon of pain suppression upon exposure to unconditioned or conditioned stressful stimuli, commonly known as stress-induced analgesia. These studies have revealed that individual sensitivity to stress-induced analgesia can vary greatly and that this sensitivity is coupled to many different phenotypes including the degree of opioid sensitivity and startle response. Furthermore, stress-induced analgesia is influenced by age, gender, and prior experience to stressful, painful, or other environmental stimuli. Stress-induced analgesia is mediated by activation of the descending inhibitory pain pathway. Pharmacological and neurochemical studies have demonstrated involvement of a large number of neurotransmitters and neuropeptides. In particular, there are key roles for the endogenous opioid, monoamine, cannabinoid, gamma-aminobutyric acid and glutamate systems. The study of stress-induced analgesia has enhanced our understanding of the fundamental physiology of pain and stress and can be a useful approach for uncovering new therapeutic targets for the treatment of pain and stress-related disorders.

Insomnia in somatoform pain disorder: sleep laboratory studies on differences to controls and acute effects of trazodone, evaluated by the Somnolyzer 24 x 7 and the Siesta database

Patients with chronic pain often suffer from sleep disturbances, specifically decreased deep sleep, and thus may get into a vicious circle which maintains their pain condition. Utilizing polysomnography and psychometry, objective and subjective sleep and awakening quality was investigated in 11 patients with nonorganic insomnia (F51.0) related to somatoform pain disorder (SPD; F45.4) as compared with age- and sex-matched healthy controls of the Siesta normative database. Patients demonstrated a markedly deteriorated Pittsburgh Sleep Quality Index, a decreased Quality of Life Index, slightly increased self-reported anxiety (Zung SAS) and depression scores (Zung SDS), as well as an increased Epworth Sleepiness Scale and International Restless Legs Syndrome Scale score. Subjective sleep and awakening quality was markedly reduced, while somatic complaints were increased. Polysomnographic evaluation by a recently developed automatic sleep classifier (Somnolyzer 24 x 7) based on the rules of Rechtschaffen and Kales demonstrated reduced slow-wave sleep (SWS), the target variable in the present study, a decreased stage shift index, increased SWS latency and stage 4 sleep (S4) latency and an increased frequency of shifts from S2 to wakefulness (W) in patients as compared with controls. Minimal oxygen saturation was found decreased, periodic leg movements (PLMs) were increased. In the morning, patients showed deteriorated well-being, drive, mood and wakefulness. There were no significant noopsychic or psychophysiological differences between patients and controls (except for a reduced numerical memory and a slightly increased morning diastolic blood pressure in patients). Subsequent evaluation of the acute effects of 100 mg of a controlled-release formulation of trazodone (Trittico retard) in the patients demonstrated an increase in the target variable SWS, accompanied by a reduction in the number of awakenings and stage shifts. It normalized the frequency of shifts from S2 to W and reduced the frequency of shifts from W to S1, from S1 to S2, as well as from any stage to S1 and S2. Trazodone, however, also significantly reduced the total sleep period and S2 and increased the latency to S1. Moreover, the drug increased the reduced minimal O(2 )saturation, reduced the arousal index and the PLMs-in-wake index and normalized the increased morning diastolic blood pressure. In conclusion, our study demonstrated that SPD induced significant changes in subjective and objective sleep and awakening quality, which were partially mitigated by trazodone therapy. The data on the target variable SWS support our hypothesis of a key-lock principle in the diagnosis and drug treatment of sleep disorders. Our study provided the first evidence on the usefulness of the Somnolyzer 24 x 7 and the Siesta database in clinical practice.

Sleep deprivation affects thermal pain thresholds but not somatosensory thresholds in healthy volunteers

OBJECTIVE

Sleep disturbances have been thought to augment pain. Sleep deprivation has been proven to produce hyperalgesic effects. It is still unclear whether these changes are truly specific to pain and not related to general changes in somatosensory functions. The aim of the present study was to evaluate the effect of total sleep deprivation on thermal pain thresholds (heat, cold) and pain complaints. Thermal detection thresholds (warmth, cold) were included as covariates to determine the contribution of somatosensory functions to changes in pain processing.

METHODS

Twenty healthy volunteers were randomly assigned either to two nights of total sleep deprivation or to two nights of undisturbed night sleep. Sleep deprivation nights were separated by two days with normal night sleep. Heat and cold pain thresholds as well as warmth and cold detection thresholds were measured by use of a peltier thermode in the evening before and the morning after each deprivation or control night. Pain complaints were examined by use of a questionnaire in parallel.

RESULTS

During treatment nights, sleep deprivation produced a significant overnight decrease in heat pain thresholds. Cold pain thresholds tended to decrease also during sleep deprivation, whereas the warmth and cold detection thresholds remained unaffected. Accordingly, no substantial contributions of the changes in thermal detection thresholds to the changes in thermal pain thresholds were determined by regression analyses. Pain complaints were not induced by sleep deprivation.

CONCLUSIONS

The present findings suggest that sleep deprivation produces hyperalgesic changes that cannot be explained by nonspecific alterations in somatosensory functions.

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

The relationship between pain and sleep seems to be reciprocal: if pain may interrupt or disturb sleep, poor sleep can also influence pain perception. However the influence of sleep disturbances on pain sensitivity remain poorly investigated. The aim of this study was to assess the effect of REM sleep deprivation on the reaction of rats subjected to different noxious stimuli. In each experiment 16 Wistar male rats were randomly assigned to two groups: controls (n=8), and REM sleep deprived rats (n=8). REM sleep deprivation was elicited using the 'inverted flower pot' technique. Four different experiments were performed to assess the sensitivity to mechanical (vocalization threshold in paw pressure), thermal (tail withdrawal latency in hot water immersion), electrical (envelope of 2nd peep in tail shock test) and chemical (analgesic behavior in formalin test) noxious stimuli. All experiments were performed over a 5-day period with baseline (day 1, day 2) in a dry environment and REM sleep deprivation (day 3, day 4 and day 5) in a wet environment. Under wet conditions, vocalization threshold in the paw pressure test (-20%, P=0.005), and tail withdrawal latency in the hot water immersion test (-21%, P=0.006) were significantly lower, and the envelope of 2nd peep in the tail electrical shock was significantly greater (+78%, P=0.009), in REM sleep deprived rats compared to controls. However, under wet conditions the mean duration of nociceptive behaviors in the formalin test did not differ between the two groups. In conclusion, REM sleep deprivation induces a significant increase in the behavioral responses to noxious mechanical, thermal and electrical stimuli in rats.

Vocalization thresholds related to noxious paw pressure are decreased by paradoxical sleep deprivation and increased after sleep recovery in rat

The aim of this study was to assess the effect of paradoxical sleep deprivation (PSD) and sleep recovery on the vocalization threshold in rats submitted to a mechanical noxious stimulus. Sixteen male Wistar rats were randomly assigned in two groups: controls (n=8), paradoxical sleep deprived rats (n=8). PSD was performed using the 'inverted flower pot' technique. Paw pressure test was used to assess the sensitivity to mechanical noxious stimulus (vocalization threshold). The experiment was divided into three periods: baseline (day 1, day 2), PSD (day 3, day 4, day 5) and recovery (day 6, day 7, day 8, day 9). After 48 and 72 h of PSD, the vocalization thresholds decreased significantly in comparison to the control rats (day 4: 245+/-21 vs. 303+/-20 g, P=0.05; day 5: 256+/-17 vs. 324+/-22 g, P=0.02). In PSD group, relative to controls, vocalization thresholds increased significantly after 48, 72, and 96 h of recovery sleep periods (day 7: 378+/-24 vs. 307+/-8 g P=0.01; day 8: 384+/-27 vs. 316+/-23 g, P=0.02; day 9: 395+/-24 vs. 328+/-15 g, P=0.02). Vocalization thresholds on day 6 were not significantly different in both groups (375+/-20 vs. 324+/-24 g, P=0.08). In conclusion, experimental PSD in rats induces a significant decrease in vocalization threshold to mechanical noxious stimulus, which is totally reversed during the sleep recovery period.

Self-injurious behavior and sleep disturbance in adults with developmental disabilities

Sleep patterns of 30 individuals with self-injurious behavior and mental retardation were compared with those of 30 matched controls residing in the same residential facility that did not self-injure. Individuals were recorded as asleep or awake during 30 min intervals for eight hours per night. The results of a Wilcoxon signed-ranks test (p < .05) indicated that individuals with self-injury slept significantly less than individuals without self-injury. chi2 analyses (p < .01) indicated significantly greater variability in the number of intervals recorded as asleep among individuals with self-injury than their matched controls. These results are congruent with previous findings of sleep disturbance among persons with mental retardation and behavior problems. The possibility of neurochemical dysregulation in sleep disturbance among individuals with daytime self-injury is discussed.

The role of sleep in migraine attacks

Migraine attacks may be precipitated by sleep deprivation or excessive sleep and sleep is also associated with relief of migraine attacks. In view of this variable relationship we studied the records of 159 consecutive outpatients of our Headache Unit. In 121 records there was reference to sleep involvement, in 55% by a single form and in 45% by more than one form. When only one form was related, relief was most common (70%). 30% of that group of patients had the migraine attack precipitated by sleep, 24% by deprivation and 6% by sleep excess. When the effects of sleep were multiple, these effects were as expected logically in 65%: "in accordance" group (e.g attack precipitated by sleep deprivation and relieved by sleep onset. In a second group, ("conflicting") where the involvement was not logical, there were three different combinations of sleep involvement, possibly due to more than one pathophysiological mechanism.

Potentiation of metaphit-induced audiogenic seizures by REM sleep deprivation in rats

The possibility that REM sleep deprivation (REMD) induced increased susceptibility of rats to the convulsive effects of metaphit was investigated. Metaphit-induced audiogenic seizures were studied in three groups of animals: 1) caged controls; 2) large platform animals; and 3) small platform, REMD animals. After 48 h of confinement to their environments the rats from all three groups were injected with metaphit (10 mg kg-1, IP) and the procedures continued for the next 24 h. Immediately after removal from platforms and at 3-h intervals thereafter all rats were individually subjected to intense sound stimulation. Convulsive responses were recorded and analyzed with respect to incidence, intensity, and duration. The REMD rats were found to be more sensitive to the convulsive effects of metaphit compared to nondeprived rats. This was manifested in significantly shorter latencies to seizures, and significantly higher incidence, severity, and duration of seizures, especially of the most severe seizure component-tonic extensor convulsion. Inducing rats to convulse while they were being REM sleep deprived eliminated the REM sleep rebound observed in REMD rats that did not convulse. The occurrence of spontaneous EEG seizures during the undisturbed recovery period reduced REM sleep rebound. The results demonstrate a reciprocal relation between seizure behavior and REM sleep.

Neurochemical perspectives of the narcoleptic syndrome

Narcolepsy has been defined as a disorder of excessive sleep often associated with cataplexy, sleep paralysis and hypnagogic hallucinations. Although the pathophysiology of the narcoleptic syndrome is not well understood, derangement in the functions of CNS catecholamines and serotonin (5-HT) have been implicated. In the present paper we summarize evidence to suggest a role for the endogenous opioids in the regulation of normal sleep and in the pathophysiology of the narcoleptic syndrome.

Deprivation of REM sleep in the rat and the opioid peptides beta-endorphin and dynorphin

Effects of 'rapid eye movement' sleep deprivation (REMd) on two opioid peptides, beta-endorphin and dynorphin, were studied in rats. Both peptides were measured by radioimmunoassay techniques. The level of beta-endorphin was estimated in the hypothalamus, in the anterior lobe of the pituitary and in the blood. The amount of dynorphin was estimated in the hypothalamus. REMd was induced for 72 h and achieved by two different methods, the platform technique and the pendulum technique. Three control groups were additionally run. As a consequence of REMd, an increase in beta-endorphin level was discovered in the blood plasma, while a small decrease was found in the hypothalamus. No changes could be detected for beta-endorphin levels in the pituitary or for hypothalamic dynorphin concentration. The deprivation effects are interpreted as belonging to a group of changes, all of which point to a small increase in tonic arousal as a result of REMd.

REM sleep deprivation (REMSD) antagonizes naloxone-precipitated withdrawal in acute morphine-dependent rats

In rats allowed undisturbed sleep (control and stress) the administration of naloxone (10 mg/kg, s.c.) to morphine (7.5 mg/kg, s.c. 90 min prior) pretreated animals precipitated a jumping behaviour. REM sleep deprivation (REMSD 96 h, prior) significantly decreased the frequency of the naloxone-precipitated jumping behaviour compared with control and stressed animals. In second animal model for morphine withdrawal, naloxone (10 mg/kg, s.c.) provoked myoclonic twitch activity (MTA) in rats previously exposed to morphine (7.5 mg/kg, s.c., 90 min prior). The intensity of naloxone-induced MTA in REM sleep deprived rats was significantly lower compared to stressed animals, but it is not different from the control group. It is suggested that REMSD interferes with a neural mechanism involved in the development of acute dependence. Results are discussed in light of a possible functional insufficiency of a mu-opioid system during REMSD.

An analgesic effect of enkephalinase inhibition is modulated by monoamine oxidase-B and REM sleep deprivations

Both the MAO-B inhibitor deprenyl (2.5-10 mg/kg, ip, 60 min prior) and the MAO-B substrate beta-phenylethylamine (PEA, 40 micrograms, icv) potentiated the analgesic action of the enkephalinase inhibitor phosphoramidon (250 micrograms, icv) in animals allowed normal sleep. The enhancing effect of PEA on phosphoramidon analgesia was further potentiated by deprenyl (5 mg/kg, ip) pretreatment. Deprenyl (5 mg/kg, ip) or PEA (40 micrograms, iv) given alone did not induce analgesia in animals allowed undisturbed sleep. REM sleep deprivation (REMSD) decreased the basal pain threshold and abolished the analgesic effect of phosphoramidon. The administration of deprenyl and/or PEA failed to restore the analgesic effect of phosphoramidon in REM sleep deprived animals. The results indicate that excess PEA has a stimulatory effect on the analgesic activity of endogenously released enkephalins in rats allowed undisturbed sleep but not in REM sleep deprived animals. It is suggested that the failure of phosphoramidon to induce analgesia after REMSD, is probably due to a functional insufficiency of an enkephalinergic system.

REM sleep deprivation decreases the grooming and shaking behaviour induced by enkephalinase inhibitor or opiate withdrawal

Intraventricular administration of enkephalinase inhibitor, phosphoramidon (1 X 10(-8)-5.6 X 10(-7) moles ICV) induced a behavioural syndrome consisting of excessive grooming with the body scratching as the most prominent symptom and wet-dog-shakes (WDS). The frequency of the phosphoramidon-induced WDS and body scratching were decreased by the pretreatment with the opiate receptor blocking agent, naltrexone (2.9 X 10(-6) moles/kg IP). Both the phosphoramidon-induced WDS in naive rats and naloxone-precipitated withdrawal WDS were decreased in REM sleep deprived rats compared with animals allowed normal sleep (control and stress groups). The results are discussed in light of a possible functional insufficiency of endorphinergic system during REMSD. It has been suggested that this insufficiency might be a background to the increased neuronal excitability during REMSD.

Endogenous opiates: 1984

This paper is the seventh in an annual series of reviews of research involving the endogenous opiate peptides, each installment being restricted to work published during the previous year. As in the past three years, the review this year is limited to non-analgesic and behavioral studies of the opiate peptides. The specific topics this year include: stress, tolerance and dependence, consummatory responses, gastric and renal activity, alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, seizures and neurological disorders, activity, and miscellaneous other topics.