The circadian clock at the intercept of sleep and pain

Circadian disruption upon painful peripheral nerve injury in mice: Temporal effects on transcriptome in pain-regulating sensory tissues

BACKGROUND

Neuropathic pain (NP) resulting from nerve damage shows diurnal fluctuation of intensity in patients, indicating circadian regulation. However, mechanisms linking NP and circadian regulation remain unclear. This study aimed to investigate time-dependent transcriptomic changes during a 24-hour period using a spared nerve injury (SNI) mouse model of NP.

METHODS

Pain-related behaviours were assessed at baseline and on days 7, 14, and 21 after SNI and control sham surgeries in C57BL/6JRJ mice. Spinal cord (SC) and periaqueductal gray (PAG) were collected 4-hourly over 24 h upon completion of behavioural testing.

RESULTS

RNA sequencing revealed 111 up- and 21 downregulated differentially expressed genes (DEGs) in the SC, and 35 up- and 33 downregulated DEGs in the PAG, across all six time points. The large majority of DEGs, 245 in the SC and 191 in the PAG, are involved in regulation of immunity. Among the top expressed genes, five DEGs in the SC, Atf3, Anxa10, Gpr151, Cxcl10, Sprr1a, and two DEGs in the PAG, Igf2 and Wnt6, were previously reported to regulate pain. Circadian analysis using CircaCompare identified 383 SC transcripts and 261 PAG transcripts with altered rhythmicity. Variability of gene expression during circadian day was increased in the SC and decreased in the PAG from the SNI mice.

CONCLUSION

These findings suggest that NP disrupts the circadian expression of rhythmic transcripts in the SC and PAG, potentially revealing new targets for chronotherapy of NP.

The associations between sleep problems and pain outcomes in people with hand osteoarthritis - Data from the Nor-hand study

Objective

To examine the relation of sleep problems to pain outcomes in people with hand osteoarthritis, and the extent to which central sensitization mediates these relationships.

Design

In total 299 participants from the Nor-Hand cohort study rated their sleep problems (no, slight, moderate or severe problems), hand pain intensity on a Numeric Rating Scale (NRS, range: 0-10) and Australian/Canadian Osteoarthritis Hand Index (AUSCAN; range: 0-20), and overall bodily pain intensity (NRS). Central sensitization was evaluated by quantitative sensory testing. All pain questionnaires were repeated after 3.5 years. We explored the associations between sleep problems at baseline and pain outcomes at baseline and follow-up and fitted natural effect models to examine the extent to which measures of central sensitization mediated the effects of sleep problems on pain. All main analyses were adjusted for age, sex, education, comorbidities, and body mass index.

Results

Slight, moderate, and severe sleep problems were reported by 33.8 ​%, 26.8 ​% and 14.3 ​%, respectively. In general, individuals with severe versus without sleep problems reported relatively more intense pain at baseline and follow up (i.e., a 1.68 (95 ​% confidence interval 0.89-2.46) higher NRS hand pain at baseline). Associations between sleep and central sensitization were weak, with no mediating effects found. For example, the indirect effect of remote pressure pain thresholds was 0.06 (-0.27, 0.39) NRS points for hand pain among individuals reporting severe sleep problems.

Conclusion

Sleep problems are commonly reported and related to pain intensity in people with hand osteoarthritis, while the underlying mechanisms and temporal relationship remain unclear.

Temporal therapy utilizing exosomes derived from M2 macrophages demonstrates enhanced efficacy in alleviating neuropathic pain in diabetic rats

Background

Diabetic pain patients have increased pain at night. Exosomes can relieve neuropathic pain. This study aimed to investigate the efficacy of exosome administration at different time points in relieving diabetic neuropathic pain (DNP) in rats.

Methods

M2 macrophages from bone marrow were induced in mice and exosomes were extracted. A diabetic rat model was induced using streptozotocin, with the mechanical withdrawal threshold (MWT) of the rats being measured at ≤ 80% of the basal value after 14 days, indicating successful construction of the DNP rat model. Exosomes were administered on three consecutive days at ZT0 (zeitgeber time) and ZT12. Parameters including blood glucose levels, body weight, MWT, and thermal withdrawal latency (TWL) were assessed in the rats. The lumbar spinal cord of rats was examined on days 21 and 28 to measure inflammatory factors and observe the expression of M1 and M2 microglia. Furthermore, microglia were exposed to lipopolysaccharide (LPS) and LPS + exosomes in a controlled in vitro setting to assess alterations in microglia phenotype involving the NF-kB p65 and IKBα inflammatory signaling pathways.

Results

The findings revealed that administration of exosomes during the rat resting period at ZT12 resulted in increased MWT and TWL, as well as a shift in microglia polarization towards the M2 phenotype. In vitro analysis indicated that exosomes influenced microglia polarization and suppressed the phosphorylation of NF-kB p65 and IKBα.

Conclusions

Temporal therapy with exosomes effectively reduces pain in DNP rats by polarizing microglia and affecting NF-kB p65 and IKBα signaling pathways.

The contribution of clock genes BMAL1 and PER2 in osteoarthritis-associated pain

Joint pain is the primary symptom of osteoarthritis (OA) and the main motivator for patients to seek medical care. OA-related pain significantly restricts joint function and diminishes quality of life. Despite the availability of various pain-relieving medications for OA, current treatment strategies often fall short in delivering adequate pain relief. Furthermore, long-term use of pain medications for OA management is frequently linked with notable side effects and toxicities, suggesting the need to explore new potential targets to treat pain in OA patients. In this context, clock genes, particularly brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (BMAL1) and period circadian protein homolog 2 (PER2), known for their role in circadian rhythms, represent promising opportunities for pharmacological interventions due to their involvement in both the development and maintenance of OA pain. While BMAL1 and PER2 have been extensively studied in neuropathic and inflammatory pain, their specific contributions to OA pain remain less clear, demanding further investigation. This narrative review aims to synthesize the relationship between OA pain and the BMAL1 and PER2 signaling pathways, ultimately exploring the potential therapeutic role of clock genes in addressing this challenging condition.

Overactive PKA signaling underlies the hyperalgesia in an ADHD mouse model

There is an intimate relationship between pain hypersensitivity and attention deficit hyperactivity disorder (ADHD); however, the underlying mechanisms are still elusive. Individuals carrying the mutation in CRY1 (c. 1657 + 3A > C), which leads to deletion of exon 11 expression in the CRY1 protein (CRY1Δ11), exhibit ADHD symptoms. Here, we demonstrate that the responses to thermal and mechanical stimuli were amplified in the Cry1Δ11 mice. RNA-sequencing analysis identified protein kinase A (PKA) signaling as being overactive in the spinal cords of Cry1Δ11 mice. The neuronal excitability was significantly enhanced in the spinal cords of Cry1Δ11 mice as determined by in vitro electrophysiology. The PKA inhibitor H89 normalized hyperalgesia in Cry1Δ11 mice, underscoring the causative effect of overactive PKA signaling. Our results thus point to the PKA signaling pathway as the underlying mechanism and a potential therapeutic target for pain hypersensitivity in a validated ADHD mouse model.

Influence of chronotype on pain incidence during early adolescence

ABSTRACT

During adolescence major shifts in sleep and circadian systems occur with a notable circadian phase delay. Yet, the circadian influence on pain during early adolescence is largely unknown. Using 2 years of data from the Adolescent Brain Cognitive Development study, we investigated the impact of chronotype on pain incidence, moderate-to-severe pain, and multiregion pain 1 year later in U.S. adolescents. Based on the Munich ChronoType Questionnaire, chronotype was calculated as the midpoint between sleep onset and offset on free days, corrected for sleep debt over the week. Adolescents reported pain presence over the past month, and if present, rated pain intensity (0-10 numerical rating scale; ≥ 4 defined as moderate-to-severe pain) and body site locations (Collaborative Health Outcomes Information Registry Body Map; ≥2 regions defined as multiregion pain). Three-level random intercept logistic regression models were specified for each pain outcome, adjusting for baseline sociodemographic and developmental characteristics. Among 5991 initially pain-free adolescents (mean age 12.0 years, SD 0.7), the mean chronotype was 3:59 am (SD 97 minutes), and the 1-year incidence of pain, moderate-to-severe pain, and multiregion pain was 24.4%, 15.2%, and 13.5%, respectively. Each hour later chronotype at baseline was associated with higher odds of developing any pain (odds ratio [OR] = 1.06, 95% confidence interval [CI] = 1.01, 1.11), moderate-to-severe pain (OR = 1.10, 95% CI = 1.05-1.17), and multiregion pain (OR = 1.08, 95% CI = 1.02-1.14) during 1-year follow-up. In this diverse U.S. adolescent sample, later chronotype predicted higher incidence of new-onset pain.

Diabetic Neuropathic Pain and Circadian Rhythm: A Future Direction Worthy of Study

More than half of people with diabetes experience neuropathic pain. Previous research has shown that diabetes patients' neuropathic pain exhibits a circadian cycle, which is characterized by increased pain sensitivity at night. Additional clinical research has revealed that the standard opioid drugs are ineffective at relieving pain and do not change the circadian rhythm. This article describes diabetic neuropathic pain and circadian rhythms separately, with a comprehensive focus on circadian rhythms. It is hoped that this characteristic of diabetic neuropathic pain can be utilized in the future to obtain more effective treatments for it.

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.

PRECISE trial (Pain RElief Combination Intervention StratEgies): protocol for the clinical trial of a pregabalin-melatonin combination for fibromyalgia

INTRODUCTION

Fibromyalgia is associated with chronic widespread pain and disturbed sleep. Multidisciplinary, multimodal management often includes pharmacotherapy; however, current drugs used to treat fibromyalgia provide meaningful benefit to only 30-60% of treated individuals. Combining two or more different drugs is common in clinical practice with the expectation of better efficacy, tolerability or both; however, further research is needed to identify which combinations actually provide added benefit. Thus, we are planning a clinical trial to evaluate melatonin (MLT)-pregabalin (PGB) combination in participants with fibromyalgia.

METHODS AND ANALYSIS

This will be a single-centre, double-blind, randomised, double-dummy, three-period, crossover trial comparing a MLT-PGB combination to each monotherapy in 54 adult participants satisfying the 2016 American College of Rheumatology criteria for fibromyalgia. Participants will receive maximally tolerated doses of MLT, PGB and MLT-PGB combination for 6 weeks. The primary outcome will be daily pain intensity (0-10); secondary outcomes will include the Fibromyalgia Impact Questionnaire, SF-36 survey, Medical Outcomes Study Sleep Scale, Beck Depression Inventory (BDI-II), adverse events and other measures. Analysis of the primary and secondary outcomes will involve a linear mixed model with sequence, period, treatment, the first-order carryover and baseline pain score as fixed effects and participant as a random effect to test whether there are any treatment differences among three treatments and to estimate the least square mean of the mean daily pain intensity for each treatment, adjusting for carryover as well as period effects (ie, stability of pain levels).

ETHICS AND DISSEMINATION

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN #18278231, has been granted ethical approval by the Queen's University Health Sciences Research Ethics Board (Queen's HSREB Protocol #6040998) and is currently under review for a Clinical Trial Application to Health Canada Natural and Non-prescription Health Products Directorate. All participants will provide written informed consent prior to trial participation. Following trial completion, results will be disseminated in one or more biomedical journal publications and presented at one or more scientific meetings.

TRIAL REGISTRATION NUMBER

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN18278231.

Increases in Sleep Difficulties and Psychological Symptoms are Associated With the Increase of Chronic Back Pain in Adolescents: The HBSC Study 2002 to 2018

Cross-national research using data from the Health Behavior in School-aged Children (HBSC) survey showed an increase in the prevalence of chronic back pain from 2002 to 2014. However, it is unknown if this trend has persisted beyond 2014. The aims of this study were to 1) determine if the prevalence of chronic back pain in girls and boys aged 11, 13, and 15 continued to increase from 2014 to 2018 and if this was the case, 2) examine whether this increase in the prevalence of chronic back pain between 2002 and 2018 was explained indirectly by increases in sleep difficulties and psychological symptoms. Data from 7,89,596 adolescents retrieved from 5 waves of the HBSC survey conducted in 2002, 2006, 2010, 2014, and 2018 in 32 countries/regions were used. Logistic regressions and path analyses were conducted. Results showed an overall increase of .5% in the prevalence of chronic back pain between 2014 and 2018, ranging from .4% for 15-year-old girls to 1.3% for 11-year-old boys, indicating a continued overall increase in chronic back pain in adolescents beyond 2014. For 13-year-old girls and for 15-year-old girls and boys, the increase in the prevalence of chronic back pain between 2002 and 2018 was partially mediated by increases in sleep difficulties, which in turn were associated with increases in psychological symptoms. The findings provide important information that may aid stakeholders in enhancing public health initiatives to prevent or reduce the increasing trend in the prevalence of chronic back pain in adolescents. PERSPECTIVE: This study shows that chronic back pain prevalence continues to increase among adolescents, with sleep difficulties and psychological symptoms contributing significantly to this trend. The findings provide insights that may inform strategies to prevent or reduce the increasing trend of chronic back pain in adolescents.

Comparison of the Effects of Desflurane and Sevoflurane on Variations in Salivary Melatonin and Sleep Disturbance After Total Knee Arthroplasty: A Single-center, Prospective, Randomized, Controlled, Open-label Study

PURPOSE

Anesthesia has been shown to disrupt the circadian rhythm. Recovery of the circadian rhythm after general anesthesia might help alleviate symptoms of insomnia and postoperative delirium. We hypothesized that recovery of the circadian rhythm is faster after total knee arthroplasty (TKA) with desflurane than with sevoflurane. This study compared the influence of sevoflurane versus desflurane anesthesia on the postoperative circadian rhythm of melatonin in adults undergoing TKA.

DESIGN

Single-center, prospective, randomized, controlled, open-label study.

METHODS

This study involved adult patients undergoing TKA at a university hospital in Japan from May 1, 2018 to December 31, 2019. The primary outcome of the study was the comparison of the effect of sevoflurane and desflurane on the circadian rhythm of salivary melatonin for 3 days postoperatively. The secondary outcomes were postoperative fatigue and sleep quality for 3 days postoperatively.

FINDINGS

Twenty-eight patients (American Society of Anesthesiologists physical status of I or II) were scheduled for TKA and randomized to receive sevoflurane (n = 14) or desflurane (n = 14) anesthesia. There was no significant difference in the melatonin concentration between the sevoflurane and desflurane groups. The salivary melatonin concentration after sevoflurane or desflurane anesthesia was significantly higher at 9:00 p.m. on a postoperative day (POD)0 and POD1 than on POD3 (P < .05). Patients in the desflurane group had significantly greater fatigue than those in the sevoflurane group at 7:00 a.m. and 12:00 p.m. on POD3 (P < .05). Patients in the sevoflurane group had a deeper sleep than those in the desflurane group on POD0 (P < .05). In the sevoflurane group, the sleep time during the night of POD2 was longer than that on POD0 (6.1 vs 4.2 hours, P < .05).

CONCLUSIONS

Under the current study conditions, desflurane was equivalent to sevoflurane in terms of the postoperative salivary melatonin concentration and sleep disturbance after TKA but not in terms of recovering the postoperative circadian rhythm.

Circadian neurogenetics and its implications in neurophysiology, behavior, and chronomedicine

The circadian rhythm affects multiple physiological processes, and disruption of the circadian system can be involved in a range of disease-related pathways. The genetic underpinnings of the circadian rhythm have been well-studied in model organisms. Significant progress has been made in understanding how clock genes affect the physiological functions of the nervous system. In addition, circadian timing is becoming a key factor in improving drug efficacy and reducing drug toxicity. The circadian biology of the target cell determines how the organ responds to the drug at a specific time of day, thus regulating pharmacodynamics. The current review brings together recent advances that have begun to unravel the molecular mechanisms of how the circadian clock affects neurophysiological and behavioral processes associated with human brain diseases. We start with a brief description of how the ubiquitous circadian rhythms are regulated at the genetic, cellular, and neural circuit levels, based on knowledge derived from extensive research on model organisms. We then summarize the latest findings from genetic studies of human brain disorders, focusing on the role of human clock gene variants in these diseases. Lastly, we discuss the impact of common dietary factors and medications on human circadian rhythms and advocate for a broader application of the concept of chronomedicine.

Epidural analgesia versus oral morphine for postoperative pain management following video-assisted thoracic surgery: A randomised, controlled, double-blind trial

BACKGROUND

The use of thoracic epidural analgesia for postoperative pain management in video-assisted thoracic surgery (VATS) is controversial. Still, the evidence on omitting it in favour of systemic opioids is inconclusive, and studies are small and non-blinded.

OBJECTIVE

We aimed to compare pain after VATS using epidural analgesia or enteral opioids for postoperative pain management.

DESIGN/SETTING/PATIENTS/INTERVENTION

A randomised, double-blind, controlled trial at a Danish tertiary hospital. Adult patients scheduled for VATS were assigned to multimodal non-opioid baseline analgesia supplemented with either thoracic epidural analgesia (TE Group) or oral morphine (OM Group) for postoperative pain management. We recorded pain five times a day, both at rest and during activity, using the Numeric Rating Scale (NRS) and categorised it into "acceptable pain" or "unacceptable pain". Unacceptable pain was defined as NRS (at rest) ≥3 or NRS (with activity) ≥5 when supplementary analgesics were given.

MAIN OUTCOME MEASURES

The primary outcomes were the proportions of patients experiencing "unacceptable pain" during the postoperative period and the use of intravenous "rescue" opioids.

RESULTS

Of the 161 included patients, 146 received the allocated treatment and their data were analysed. At rest, 34% of patients in the TE Group and 64% of patients in the OM Group experienced unacceptable pain during the study period, a significant between-group difference of 30% ( P  < 0.0005). During activity these percentages were 32% of patients in the TE Group and 59% in the OM group, a difference of 27% ( P  < 0.005). The median intravenous rescue morphine consumption during the study period was 4.5 [interquartile range (IQR), 0-10.0] mg in the TE Group and 7.5 [0-19.0] mg in the OM Group ( P  < 0.005).

CONCLUSION

Epidural analgesia provided better pain relief after VATS than oral morphine. The between-group difference in rescue intravenous morphine consumption was statistically significant but clinically irrelevant.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT02359175).

Sleep disturbances are associated with pain intensity and pain-related functional interference in patients experiencing orofacial pain

BACKGROUND

Sleep and pain have a reciprocal relationship, interacting with psychosocial aspects including depression, anxiety, somatization and significant stressful events.

OBJECTIVE

The aim of this study was to assess patients with oro-facial pain (OFP) and related sleep disturbances and determine the strongest psychosocial correlates.

METHODS

A cross-sectional study of anonymized data of consecutive patients with OFP {January 2019 and February 2020} were analysed. Diagnostic and Axis-II data were integrated to assess the relationship between sleep disturbances, measured using Chronic Pain Sleep Inventory, and demographic factors, clinical comorbidities, recent stressful events, pain severity and pain- and psychological-related function.

RESULTS

Five out of six patients with OFP were presented with pain-related sleep disturbances. Sleep problems were enhanced in patients with primary oro-facial headache compared with other OFP conditions. However, once the level of pain intensity and interference was accounted for, primary headache, was not a significant correlate of pain-related sleep disturbances. Multivariate analysis revealed (average) pain severity and pain interference were both significantly associated with sleep problems. There were also significant independent associations of sleep problems with somatization levels and reported experience of recent stressful events.

CONCLUSION

Identifying sleep problems as a part of OFP management may be beneficial and could result in better management outcomes.

Efficacy of combined strategies of physical activity, diet and sleep disorders as treatment in patients with chronic shoulder pain. A systematic review

Introduction: The objective of this systematic review was to analyze the existing scientific evidence on the influence of dietary strategies, exercise, and sleep disorders on the symptomatology of patients with chronic shoulder pain, as well as to assess the methodological quality of the literature collected. Methods: The selection criteria were as follows: we included randomized controlled clinical trials written in English that investigated the effects of such interventions in patients with chronic shoulder pain and excluded studies where pre-operative rehabilitation or rehabilitation combined with corticosteroid injections was performed. We searched six databases Pubmed, Cochrane Library, Web of Science, CINAHL, Sportdiscus and Scopus, using the keywords "shoulder pain," "fasting," "physical therapy modalities," "rehabilitation," "exercise," "circadian clocks," and "chronic pain" to select randomized controlled clinical trials conducted in humans and written in English. The last search was conducted on 24/01/2023. (PROSPERO:CRD42023379925). Results: We used the tool proposed by the Cochrane Handbook to assess the risk of bias in the included studies of the 17 studies included, nine had a high risk of bias, two studies had an unclear risk of bias, and the remaining six studies had a low risk of bias. A total of 17 articles were selected, including 10 studies that showed a positive influences of exercise on chronic shoulder pain and five studies that showed a negative influence of sleep disorders on this patient profile. The remaining two articles analyzed the influence of nutritional strategies and metabolic problems in patients with chronic shoulder pain. The total sample size of the 17 included articles amounted to 9,991 individuals. Discussion: Studies confirm that exercise generates a hypoalgesic effect that improves chronic shoulder pain, functionality, and quality of life. Although dietary strategies and sleep disorders are known to influence chronic shoulder pain, there is a lack of studies that conduct interventions on these problems to assess how chronic shoulder pain varies.

Sleep disturbance and dysregulation of circadian clock machinery in sudden sensorineural hearing loss

BACKGROUND

The cochlea contains a robust biological clock associated with auditory function, exhibiting diurnal sensitivity to noise or ototoxicity.

OBJECTIVES

We examined the relationship between disrupted circadian rhythm and altered expression of circadian clock genes in patients with sudden sensorineural hearing loss (SSNHL) and explored whether the circadian clock genes serve as prognostic biomarkers.

MATERIAL AND METHODS

Twelve patients with SSNHL were enrolled study group. Twelve people with normal hearing were enrolled voluntarily for comparison. Audiological evaluation was performed to evaluate hearing thresholds. Korean version of the Pittsburgh Sleep Quality Index Questionnaire was performed to evaluate sleep quality and patterns. Circadian clock genes including for PERI, PER2, PER3, CRYI, CRY2, CLOCK, ARNTL, CSNKIE, and TIMELESS expression in blood were evaluated using real-time quantitative PCR method.

RESULTS

Compared with healthy controls without hearing loss, most of the circadian clock genes were markedly downregulated, coupled with low sleep quality and disturbing patterns, in patients with SSNHL. Intriguingly, a weak correlation between hearing improvement following steroid treatment and altered levels of circadian clock genes was observed.

CONCLUSIONS AND SIGNIFICANCE

This study provides an additional basis for the relevance of disrupted circadian rhythm to SSNHL and suggests a possible prognostic biomarker for SSNHL treatment.

The effect of thioredoxin-1 in a rat model of traumatic brain injury depending on diurnal variation

INTRODUCTION

Traumatic brain injury (TBI) is a public health concern with limited treatment options because it causes a cascade of side effects that are the leading cause of hospital death. Thioredoxin is an enzyme with neuroprotective properties such as antioxidant, antiapoptotic, immune response modulator, and neurogenic, among others; it has been considered a therapeutic target for treating many disorders.

METHODS

The controlled cortical impact (CCI) model was used to assess the effect of recombinant human thioredoxin 1 (rhTrx1) (1 μg/2 μL, intracortical) on rats subjected to TBI at two different times of the light-dark cycle (01:00 and 13:00 h). We analyzed the food intake, body weight loss, motor coordination, pain perception, and histology in specific hippocampus (CA1, CA2, CA3, and Dental Gyrus) and striatum (caudate-putamen) areas.

RESULTS

Body weight loss, reduced food intake, spontaneous pain, motor impairment, and neuronal damage in specific hippocampus and striatum regions are more evident in rats subjected to TBI in the light phase than in the dark phase of the cycle and in groups that did not receive rhTrx1 or minocycline (as positive control). Three days after TBI, there is a recovery in body weight, food intake, motor impairment, and pain, which is more pronounced in the rats subjected to TBI at the dark phase of the cycle and those that received rhTrx1 or minocycline.

CONCLUSIONS

Knowing the time of day a TBI occurs in connection to the neuroprotective mechanisms of the immune response in diurnal variation and the usage of the Trx1 protein might have a beneficial therapeutic impact in promoting quick recovery after a TBI.

The Circadian Clocks, Oscillations of Pain-Related Mediators, and Pain

The circadian clock is a biochemical oscillator that is synchronized with solar time. Normal circadian rhythms are necessary for many physiological functions. Circadian rhythms have also been linked with many physiological functions, several clinical symptoms, and diseases. Accumulating evidence suggests that the circadian clock appears to modulate the processing of nociceptive information. Many pain conditions display a circadian fluctuation pattern clinically. Thus, the aim of this review is to summarize the existing knowledge about the circadian clocks involved in diurnal rhythms of pain. Possible cellular and molecular mechanisms regarding the connection between the circadian clocks and pain are discussed.

The complexities of the sleep-pain relationship in adolescents: A critical review

Chronic pain is a common and disabling condition in adolescents. Disturbed sleep is associated with many detrimental effects in adolescents with acute and chronic pain. While sleep and pain are known to share a reciprocal relationship, the sleep-pain relationship in adolescence warrants further contextualization within normally occurring maturation of several biopsychological processes. Since sleep and pain disorders begin to emerge in early adolescence and are often comorbid, there is a need for a comprehensive picture of their interrelation especially related to temporal relationships and mechanistic drivers. While existing reviews provide a solid foundation for the interaction between disturbed sleep and pain in youth, we will extend this review by highlighting current methodological challenges for both sleep and pain assessments, exploring the recent evidence for directionality in the sleep-pain relationship, reviewing potential mechanisms and factors underlying the relationship, and providing direction for future investigations. We will also highlight the potential role of digital technologies in advancing the understanding of the sleep and pain relationship. Ultimately, we anticipate this information will facilitate further research and inform the management of pain and poor sleep, which will ultimately improve the quality of life in adolescents and reduce the risk of pain persisting into adulthood.

The disruptive relationship among circadian rhythms, pain, and opioids

Pain behavior and the systems that mediate opioid analgesia and opioid reward processing display circadian rhythms. Moreover, the pain system and opioid processing systems, including the mesolimbic reward circuitry, reciprocally interact with the circadian system. Recent work has demonstrated the disruptive relationship among these three systems. Disruption of circadian rhythms can exacerbate pain behavior and modulate opioid processing, and pain and opioids can influence circadian rhythms. This review highlights evidence demonstrating the relationship among the circadian, pain, and opioid systems. Evidence of how disruption of one of these systems can lead to reciprocal disruptions of the other is then reviewed. Finally, we discuss the interconnected nature of these systems to emphasize the importance of their interactions in therapeutic contexts.

Circadian pain patterns in human pain conditions - A systematic review

BACKGROUND

Chronobiology is the science of how physiological processes in the body follow a pattern of time. Pain has been shown to follow a circadian rhythm, with different types of pain having variable expression along this rhythm.

OBJECTIVE

This article reviews the nature of diurnal variations in pain along with a discussion of the mechanisms of circadian rhythm of pain.

EVIDENCE REVIEW

We conducted a literature search on the PubMed and Google Scholar electronic databases, through April 2022. Publications were screened for English language, full-text availability, and human subjects. Randomized controlled trials and observational trials were included. Data were extracted from studies on patients with acute or chronic pain phenotypes, which provide pain severity data and corresponding diurnal time points.

FINDINGS

The literature search led to the inclusion of 39 studies. A circadian pattern of pain was found to be present in nociceptive, neuropathic, central, and mixed pain states. Postoperative pain, fibromyalgia, trigeminal neuralgia, and migraines were associated with higher pain scores in the morning. Temporomandibular joint pain, neuropathic pain, labor pain, biliary colic, and cluster headaches increased throughout the day to reach a peak in the evening or night. Arthritis and cancer pain were not associated with any circadian rhythmicity. Furthermore, the circadian rhythm of pain was not found to be altered in patients on analgesics.

CONCLUSION

The results of this review suggest that an understanding of diurnal variation may help improve therapeutic strategies in pain management, for instance through analgesic titration.

An Overview of the Circadian Clock in the Frame of Chronotherapy: From Bench to Bedside

Most living organisms in both the plant and animal kingdoms have evolved processes to stay in tune with the alternation of day and night, and to optimize their physiology as a function of light supply. In mammals, a circadian clock relying on feedback loops between key transcription factors will thus control the temporally regulated pattern of expression of most genes. Modern ways of life have highly altered the synchronization of human activities with their circadian clocks. This review discusses the links between an altered circadian clock and the rise of pathologies. We then sum up the proofs of concept advocating for the integration of circadian clock considerations in chronotherapy for health care, medicine, and pharmacotherapy. Finally, we discuss the current challenges that circadian biology must face and the tools to address them.

Nature and nurture. Genetic and environmental factors on the relationship between back pain and sleep quality

BACKGROUND

Chronic low back pain (LBP), neck pain (NP), and sleep quality (SQ) are genetically influenced. All three conditions frequently co-occur and shared genetic etiology on a pairwise base has been reported. However, to our knowledge no study has yet investigated if these three conditions are influenced by the same genetic and environmental factors and the extent and pattern of genetic overlap between them, hence the current research.

METHODS

The sample included 2134 participants. Lifetime prevalence of NP and LBP were assessed through a dichotomous self-reported question derived from the Spanish National Health Survey. SQ was measured using the Pittsburgh Sleep Quality Index Questionnaire. A common pathway model with sleep quality and back pain as latent factors was fitted.

RESULTS

Our results highlight that a latent back pain factor, including both NP and LBP, is explained by both genetic (41%) and environmental (59%) factors. There are also significant unique environmental factors for NP (33%) and LBP (37%) respectively. Yet, specific genetic factors were scant (9%) for NP and negligible for LBP (0%). Genetic and environmental factors affecting SQ only contribute with 3% and 5% of the variance, respectively, to the common latent back pain variable.

CONCLUSIONS

NP and LBP share most of their genetic variance, while environmental effects show greater specificity for each of the back pain locations. Associations with SQ were of a limited magnitude.

A Scoping Review of the Diurnal Variation in the Intensity of Neuropathic Pain

BACKGROUND

Recent studies have suggested that neuropathic pain exhibits a daily diurnal pattern, with peak levels usually occurring in the late afternoon to evening and the trough in the morning hours, although literature on this topic has been sparse. This scoping review examines current evidence on the chronobiology of neuropathic pain both in animal models and in humans with neuropathic pain.

METHODS

A literature search was conducted in major medical databases for relevant articles on the chronobiology of neuropathic pain both in animal models and in humans with neuropathic pain. Data extracted included details of specific animal models or specific neuropathic pain conditions in humans, methods and timing of assessing pain severity, and specific findings of diurnal variation in pain intensity or its surrogate markers.

RESULTS

Thirteen animal and eight human studies published between 1976 and 2020 were included in the analysis. Seven of the 13 animal studies reported specific diurnal variation in pain intensity, with five of the seven studies reporting a trend toward increased sensitivity to mechanical allodynia or thermal hyperalgesia in the late light to dark phase. All eight studies in human subjects reported a diurnal variation in the intensity of neuropathic pain, where there was an increase in pain intensity through the day with peaks in the late evening and early night hours.

CONCLUSIONS

Studies included in this review demonstrated a diurnal variation in the pattern of neuropathic pain that is distinct from the pattern for nociceptive pain. These findings have implications for potential therapeutic strategies for neuropathic pain.

Sleep phase and pre-sleep arousal predicted co-developmental trajectories of pain and insomnia within adolescence

The onset of both chronic pain and insomnia is high during adolescence. Although a bidirectional relationship between pain and insomnia has support, how pain and sleep co-develop throughout adolescence remains unknown. Sleep–wake patterns, pre-sleep behavior and pre-sleep arousal may influence the co-development of pain and insomnia. Four waves of longitudinal self-report data were used (N^baseline = 2767, Age^baseline M = 13.65 years, SD = 0.65). Multidimensional growth mixture modeling was used to identify four subgroups of adolescents with different concurrent trajectories of pain and insomnia. The trajectories followed each other across time in all classes: one class of consistently low pain and insomnia (68.7%), one class with persistent high symptoms (4.9%), as well as one class of increasing (13.9%), and one of decreasing (12.5%), trajectories. Later sleep–wake patterns and more pre-sleep cognitive-emotional arousal predicted both increasing and decreasing trajectories of concurrent pain and insomnia. The current study showed that developmental trajectories of pain and insomnia follow each other within adolescents and across adolescence. Both sleep-phase focused interventions as well as psychological interventions that focus on pre-sleep cognitive-emotional arousal may prove beneficial for adolescents with comorbid pain and insomnia.

Longitudinal Analysis of Sleep Disturbance in Breast Cancer Survivors

BACKGROUND

Breast cancer survivors (BCS) often report poor sleep quality and wakefulness throughout the night as the greatest challenges experienced during and posttreatment.

OBJECTIVES

This study aimed to elucidate characteristics of sleep disturbances and determine potential predictors that affect sleep disturbances in BCS for 2 years postchemotherapy.

METHODS

This is a secondary analysis of data from the EPIGEN study, which longitudinally examined sociodemographic and cancer-related factors, lifestyle, symptom characteristics, and epigenetic factors at baseline prior to chemotherapy (T1), the midpoint (T2), 6-month (T3), 1-year (T4), and 2-year (T5) time points postchemotherapy. Temporal lifestyle changes, symptom characteristics, and epigenetic factors were explored using linear mixed-effects models with a random intercept. A linear regression model was fitted to identify significant predictors of sleep disturbances at each time point.

RESULTS

In 74 BCS with an average age of 51 years and 70% non-Hispanic White, BCS experienced severe sleep disturbances at T2, which gradually improved over time. Significant temporal changes in midsleep awakenings, early awakenings, and fatigue at work were observed, with disturbances being elevated at T2. Anxiety (T1, T2, and T4), fatigue (T3 and T4), and perceived stress (T3) were significant predictors after adjusting for radiation therapy, surgery, and adjuvant endocrine therapy.

DISCUSSION

This study highlights that predictors of sleep disturbances change over time, with anxiety being a factor earlier in the treatment trajectory (prechemotherapy) and continuing over time with fatigue and perceived stress being involved later in the treatment trajectory. Our results indicate that symptom management strategies to address sleep disturbances should be tailored to the temporal factors that may change in severity during active treatment and early survivorship period. Findings gained from this study on sleep disturbance patterns and the potential risk factors can be incorporated into clinical practice in planning education and developing interventions.

The relationship between chronotypes and musculoskeletal problems in male automobile manufacturing workers

Background

Previous studies have shown that morning types are less sensitive to pain. This study aimed to examine the relationship between chronotypes and musculoskeletal problems in workers with musculoskeletal burdens at work.

Methods

This cross-sectional study included 119 male production workers from a large automobile manufacturing plant. All the participants worked 2 shifts and worked on the automobile assembly line. Data were obtained using structured questionnaires, including the reduced Morningness-Eveningness Questionnaire (rMEQ), and musculoskeletal symptom questionnaire. Participants with an rMEQ score of 18 points or more were defined as morning-type workers (MTWs). Participants whose scores were less than 18 points were defined as neither-type workers (NTWs).

Results

The arithmetic mean age was 51.8 ± 5.3 years. MTWs and NTWs accounted for 35.3% and 64.7% of the total participants, respectively. Evening- and intermediate-type workers accounted form 6.7% and 58.0% of the participants, respectively. There was no significant difference in the health indicators when the MTW and NTW groups were compared. However, the musculoskeletal symptom questionnaire demonstrated a significant difference between the MTW and NTW groups. In the preceding year, the MTW group had significantly lower musculoskeletal pain and treatment ratios compared to the NTW group (35.7% vs. 62.3%, p = 0.005 and 14.3% vs. 32.5%, p = 0.031, respectively). After adjusting for variables, the odds ratio (OR) for musculoskeletal pain was significantly higher in the NTW group than in the MTW group (OR, 3.112; 95% confidence interval, 1.285–7.535; p = 0.012).

Conclusions

In this study, the musculoskeletal pain ratio was significantly lower for MTWs when compared to NTWs. Chronotypes could play an important role in work-related musculoskeletal disorders. Further, larger-scale, follow-up studies on chronotypes are required to assist in the prevention of musculoskeletal disorders in future.

Circadian rhythms and pain

The goal of this review is to provide a perspective on the nature and importance of the relationship between the circadian and pain systems. We provide: 1) An overview of the circadian and pain systems, 2) a review of direct and correlative evidence that demonstrates diurnal and circadian rhythms within the pain system; 3) a perspective highlighting the need to consider the role of a proposed feedback loop of circadian rhythm disruption and maladaptive pain; 4) a perspective on the nature of the relationship between circadian rhythms and pain. In summary, we propose that there is no single locus responsible for producing the circadian rhythms of the pain system. Instead, circadian rhythms of pain are a complex result of the distributed rhythms present throughout the pain system, especially those of the descending pain modulatory system, and the rhythms of the systems with which it interacts, including the opioid, endocrine, and immune systems.

Melatonin Moderates the Triangle of Chronic Pain, Sleep Architecture and Immunometabolic Traffic

Preclinical as well as human studies indicate that melatonin is essential for a physiological sleep state, promotes analgesia and is involved in immunometabolic signaling by regulating neuroinflammatory pathways. Experimental and clinical neuromodulation studies for chronic pain treatment suggest that neurostimulation therapies such as spinal cord stimulation, vagus nerve stimulation and dorsal root ganglion stimulation have an impact on circulating inflammatory mediators in blood, cerebrospinal fluid and saliva. Herein, we provide an overview of current literature relevant for the shared pathways of sleep, pain and immunometabolism and elaborate the impact of melatonin on the crossroad of sleep, chronic pain and immunometabolism. Furthermore, we discuss the potential of melatonin as an adjunct to neurostimulation therapies. In this narrative review, we addressed these questions using the following search terms: melatonin, sleep, immunometabolism, obesity, chronic pain, neuromodulation, neurostimulation, neuroinflammation, molecular inflammatory phenotyping. So far, the majority of the published literature is derived from experimental studies and studies specifically assessing these relationships in context to neurostimulation are sparse. Thus, the adjunct potential of melatonin in clinical neurostimulation has not been evaluated under the umbrella of randomized-controlled trials and deserves increased attention as melatonin interacts and shares pathways relevant for noninvasive and invasive neurostimulation therapies.

Time-of-day as a critical biological variable

Time-of-day is a crucial, yet often overlooked, biological variable in biomedical research. We examined the top 25 most cited papers in several domains of behavioral neuroscience to determine whether time-of-day information was reported. The majority of studies report behavioral testing conducted during the day, which does not coincide with the optimal time to perform the testing from an functional perspective of the animals being tested. The majority of animal models used in biomedical research are nocturnal rodents; thus, testing during the light phase (i.e. animals' rest period) may alter the results and introduce variability across studies. Time-of-day is rarely considered in analyses or reported in publications; the majority of publications fail to include temporal details when describing their experimental methods, and those few that report testing during the dark rarely report whether measures are in place to protect from exposure to extraneous light. We propose that failing to account for time-of-day may compromise replication of findings across behavioral studies and reduce their value when extrapolating results to diurnal humans.

CGRP induces migraine-like symptoms in mice during both the active and inactive phases

BACKGROUND

Circadian patterns of migraine attacks have been reported by patients but remain understudied. In animal models, circadian phases are generally not taken into consideration. In particular, rodents are nocturnal animals, yet they are most often tested during their inactive phase during the day. This study aims to test the validity of CGRP-induced behavioral changes in mice by comparing responses during the active and inactive phases.

METHODS

Male and female mice of the outbred CD1 strain were administered vehicle (PBS) or CGRP (0.1 mg/kg, i.p.) to induce migraine-like symptoms. Animals were tested for activity (homecage movement and voluntary wheel running), light aversive behavior, and spontaneous pain at different times of the day and night.

RESULTS

Peripheral administration of CGRP decreased the activity of mice during the first hour after administration, induced light aversive behavior, and spontaneous pain during that same period of time. Both phenotypes were observed no matter what time of the day or night they were assessed.

CONCLUSIONS

A decrease in wheel activity is an additional clinically relevant phenotype observed in this model, which is reminiscent of the reduction in normal physical activity observed in migraine patients. The ability of peripheral CGRP to induce migraine-like symptoms in mice is independent of the phase of the circadian cycle. Therefore, preclinical assessment of migraine-like phenotypes can likely be done during the more convenient inactive phase of mice.

Mouse Anesthesia: The Art and Science

There is an art and science to performing mouse anesthesia, which is a significant component to animal research. Frequently, anesthesia is one vital step of many over the course of a research project spanning weeks, months, or beyond. It is critical to perform anesthesia according to the approved research protocol using appropriately handled and administered pharmaceutical-grade compounds whenever possible. Sufficient documentation of the anesthetic event and procedure should also be performed to meet the legal, ethical, and research reproducibility obligations. However, this regulatory and documentation process may lead to the use of a few possibly oversimplified anesthetic protocols used for mouse procedures and anesthesia. Although a frequently used anesthetic protocol may work perfectly for each mouse anesthetized, sometimes unexpected complications will arise, and quick adjustments to the anesthetic depth and support provided will be required. As an old saying goes, anesthesia is 99% boredom and 1% sheer terror. The purpose of this review article is to discuss the science of mouse anesthesia together with the art of applying these anesthetic techniques to provide readers with the knowledge needed for successful anesthetic procedures. The authors include experiences in mouse inhalant and injectable anesthesia, peri-anesthetic monitoring, specific procedures, and treating common complications. This article utilizes key points for easy access of important messages and authors’ recommendation based on the authors’ clinical experiences.

Pre-sleep cognitive arousal exacerbates sleep disturbance in chronic pain: an exploratory daily diary and actigraphy study

OBJECTIVES

Insomnia is commonly comorbid with chronic pain, and typically leads to worse outcomes. Two factors that could contribute to a cycle of pain and sleeplessness are pre-sleep cognitive arousal (repetitive thought processes) and low mood. This study aimed to examine how pain, sleep disturbance, mood, and pre-sleep cognitive arousal inter-relate, to determine whether low mood or pre-sleep cognitive arousal contribute to a vicious cycle of pain and insomnia.

METHODS

Forty seven chronic pain patients completed twice daily diary measures and actigraphy for one week. Analyses investigated the temporal and directional relationships between pain intensity, sleep quality, time awake after sleep onset, anhedonic and dysphoric mood, and pre-sleep cognitive arousal. Fluctuations in predictor variables were used to predict outcome variables the following morning using mixed-effects modelling.

RESULTS

For people with chronic pain, an evening with greater pre-sleep cognitive arousal (relative to normal) led to a night of poorer sleep (measured objectively and subjectively), lower mood in the morning, and a greater misperception of sleep (underestimating sleep). A night of poorer sleep quality led to greater pain the following morning. Fluctuations in pain intensity and depression did not have a significant influence on subsequent sleep.

CONCLUSIONS

For people with chronic pain, cognitive arousal may be a key variable exacerbating insomnia, which in turn heightens pain. Future studies could target cognitive arousal to assess effects on sleep and pain outcomes.

Orofacial musculoskeletal pain: An evidence-based bio-psycho-social matrix model

Pain is a multidimensional experience comprising sensory-discriminative, affective-motivational, and cognitive-evaluative dimensions. Clinical and research findings have demonstrated a complex interplay between social burdens, individual coping strategies, mood states, psychological disorders, sleep disturbances, masticatory muscle tone, and orofacial musculoskeletal pain. Accordingly, current classification systems for orofacial pain require psychosocial assessments to be an integral part of the multidimensional diagnostic process. Here, we review evidence on how psychosocial and biological factors may generate and perpetuate musculoskeletal orofacial pain. Specifically, we discuss studies investigating a putative causal relationship between stress, bruxism, and pain in the masticatory system. We present findings that attribute brain structures various roles in modulating pain perception and pain-related behavior. We also examine studies investigating how the nervous and immune system on cellular and molecular levels may account for orofacial nociceptive signaling. Furthermore, we review evidence pointing towards associations between orofacial musculoskeletal pain and neuroendocrine imbalances, sleep disturbances, and alterations of the circadian timing system. We conclude with several proposals that may help to alleviate orofacial pain in the future.

Daily associations between sleep and pain in patients with chronic musculoskeletal pain

Patients with chronic pain commonly report sleep problems, and the evidence for a relationship between sleep disturbance and pain seems robust. The day-to-day associations between these constructs are less well studied, particularly with objective sleep measures such as actigraphy. Moreover, the concurrent presence of negative affective symptoms, as well as seasonality effects at extreme latitudes may complicate it further. Here, we studied 56 patients with chronic primary musculoskeletal pain conditions, contributing data in two separate 7-day data-collection periods during the summer and winter, respectively. The effect of self-reported sleep quality, and actigraphy measured sleep duration, efficiency and timing on next-day pain, as well as the effect of pain on the same sleep indices were estimated by generalised linear mixed regression models. The models were additionally adjusted for age, sex, education, data collection period, weekend, season and mental distress, with the latter two also specified as moderators. We observed a significant effect of pain as a predictor of next-night sleep quality (p = .003) and marginally of next-night sleep duration (p = .079). Conversely, sleep quality tentatively predicted next-day pain (p = .063). No other day-to-day associations were present. Mental distress was the strongest predictor of pain, but it did not modify the sleep-pain associations, nor did season. In conclusion pain, sleep quality and mental distress are closely related, underscoring the importance of encompassing this complexity in assessment and treatment of patients with chronic pain.