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Group III/IV muscle afferents transduce nociceptive signals and modulate exercise pressor reflexes (EPRs). However, the mechanisms governing afferent responsiveness to dually modulate these processes are not well characterized. We and others have shown that ischemic injury can induce both nociception-related behaviors and exacerbated EPRs in the same mice. This correlated with primary muscle afferent sensitization and increased expression of glial cell line-derived neurotrophic factor (GDNF) in injured muscle and increased expression of GDNF family receptor α1 (GFRα1) in dorsal root ganglia (DRG). Here, we report that increased GDNF/GFRα1 signaling to sensory neurons from ischemia/reperfusion-affected muscle directly modulated nociceptive-like behaviors and increased exercise-mediated reflexes and group III/IV muscle afferent sensitization. This appeared to have taken effect through increased cyclic adenosine monophosphate (cAMP) response element binding (CREB)/CREB binding protein-mediated expression of the purinergic receptor P2X5 in the DRGs. Muscle GDNF signaling to neurons may, therefore, play an important dual role in nociception and sympathetic reflexes and could provide a therapeutic target for treating complications from ischemic injuries.
Learn More >Oxidative stress is an important driver of neuropathic painDimethyl fumarate activates nuclear factor erythroid 2-related factor 2, increasing the expression of multiple antioxidant genes WHAT THIS ARTICLE TELLS US THAT IS NEW: Using a rat model of nerve injury, both male and female animals displayed reduced mechanical and nociceptive sensitization when given dimethyl fumarateDimethyl fumarate administration increased superoxide dismutase activity while decreasing cytokine expression and improving mitochondrial bioenergetics BACKGROUND:: Available treatments for neuropathic pain have modest efficacy and significant adverse effects, including abuse potential. Because oxidative stress is a key mechanistic node for neuropathic pain, the authors focused on the master regulator of the antioxidant response-nuclear factor erythroid 2-related factor 2 (NFE2L2; Nrf2)-as an alternative target for neuropathic pain. The authors tested whether dimethyl fumarate (U.S. Food and Drug Administration-approved treatment for multiple sclerosis) would activate NFE2L2 and promote antioxidant activity to reverse neuropathic pain behaviors and oxidative stress-dependent mechanisms.
Learn More >A major function of GPCRs is to inhibit presynaptic neurotransmitter release, requiring ligand-activated receptors to couple locally to effectors at terminals. The current understanding of how this is achieved is through receptor immobilization on the terminal surface. Here, we show that opioid peptide receptors, GPCRs that mediate highly sensitive presynaptic inhibition, are instead dynamic in axons. Opioid receptors diffuse rapidly throughout the axon surface and internalize after ligand-induced activation specifically at presynaptic terminals. We delineate a parallel regulated endocytic cycle for GPCRs operating at the presynapse, separately from the synaptic vesicle cycle, which clears activated receptors from the surface of terminals and locally reinserts them to maintain the diffusible surface pool. We propose an alternate strategy for achieving local control of presynaptic effectors that, opposite to using receptor immobilization and enforced proximity, is based on lateral mobility of receptors and leverages the inherent allostery of GPCR-effector coupling.
Learn More >To examine the cardiovascular, cerebrovascular, and peripheral vascular safety of erenumab across migraine prevention studies.
Learn More >Genetic variation in melanocortin-1 receptor (MC1R) has a known role in red hair. Studies on responses to noxious stimuli in red-haired individuals have also been conducted, with mixed findings. To investigate a possible divergence between variants responsible for red hair and pain sensitivity, we performed a gene-wide association analysis in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) cohort. All genotyped (17) MC1R variants were tested for association with heat pain temporal summation and sensitivity. Our analyses showed an association for pain sensitivity with the 5'-UTR, tagged by rs3212361, and one missense variant, rs885479 (R163Q), previously shown to be weakly associated with red hair. For both variants, the minor allele was protective. These results were validated in the 500,000-person U.K. Biobank (UKBB) cohort, where the minor alleles of rs3212361 and rs885479 were associated with a reduced count of persistent pain conditions as well as individual pain conditions. Haplotype association analysis revealed a possible joint effect from the two individual variants. The 5'-UTR variant rs3212361 was further identified as an expression quantitative trait locus (eQTL), associated with reduced transcript levels of MC1R in the brain and in the peripheral tibial nerve. Hair colour association analysis of the loss-of-function 5'-UTR rs3212361 allele identified association with red hair, and red hair colour itself was associated with a reduced count of persistent pain conditions. Together, our results suggest that primarily different mechanisms – affecting expression levels versus protein activity – mediated by different genetic variants in the MC1R locus contribute to red hair and pain.
Learn More >As a protective mechanism, the cornea is sensitive to noxious stimuli. Here, we show that in mice, a high proportion of corneal TRPM8 cold-sensing fibers express the heat-sensitive TRPV1 channel. Despite its insensitivity to cold, TRPV1 enhances membrane potential changes and electrical firing of TRPM8 neurons in response to cold stimulation. This elevated neuronal excitability leads to augmented ocular cold nociception in mice. In a model of dry eye disease, the expression of TRPV1 in TRPM8 cold-sensing fibers is increased, and results in severe cold allodynia. Overexpression of TRPV1 in TRPM8 sensory neurons leads to cold allodynia in both corneal and non-corneal tissues without affecting their thermal sensitivity. TRPV1-dependent neuronal sensitization facilitates the release of the neuropeptide substance P from TRPM8 cold-sensing neurons to signal nociception in response to cold. Our study identifies a mechanism underlying corneal cold nociception and suggests a potential target for the treatment of ocular pain.
Learn More >Anecdotal evidence that cannabis preparations have medical benefits together with the discovery of the psychotropic plant cannabinoid Δ-tetrahydrocannabinol (THC) initiated efforts to develop cannabinoid-based therapeutics. These efforts have been marked by disappointment, especially in relation to the unwanted central effects that result from activation of cannabinoid receptor 1 (CB1), which have limited the therapeutic use of drugs that activate or inactivate this receptor. The discovery of CB2 and of endogenous cannabinoid receptor ligands (endocannabinoids) raised new possibilities for safe targeting of this endocannabinoid system. However, clinical success has been limited, complicated by the discovery of an expanded endocannabinoid system – known as the endocannabinoidome – that includes several mediators that are biochemically related to the endocannabinoids, and their receptors and metabolic enzymes. The approvals of nabiximols, a mixture of THC and the non-psychotropic cannabinoid cannabidiol, for the treatment of spasticity and neuropathic pain in multiple sclerosis, and of purified botanical cannabidiol for the treatment of otherwise untreatable forms of paediatric epilepsy, have brought the therapeutic use of cannabinoids and endocannabinoids in neurological diseases into the limelight. In this Review, we provide an overview of the endocannabinoid system and the endocannabinoidome before discussing their involvement in and clinical relevance to a variety of neurological disorders, including Parkinson disease, Alzheimer disease, Huntington disease, multiple sclerosis, amyotrophic lateral sclerosis, traumatic brain injury, stroke, epilepsy and glioblastoma.
Learn More >Painful distal symmetrical polyneuropathy is common in HIV and is associated with reduced quality of life. Research has not explored the experience of neuropathic pain in people with HIV from a person-centred perspective. Therefore, a qualitative interview study was conducted to more deeply understand the experience and impact of neuropathic pain in this population. Semi-structured interviews were conducted with 26 people with HIV and peripheral neuropathic pain symptoms. Interviews explored the impact of pain and participants' pain management strategies. Interviews were transcribed verbatim and analysed using thematic analysis. Four themes and 11 subthemes were identified. Theme one reflects the complex characterisation of neuropathic pain, including the perceived unusual nature of this pain and diagnostic uncertainty. Theme two centred on the interconnected impacts of pain on mood and functioning and includes how pain disrupts relationships and threatens social inclusion. Theme three reflects the struggle for pain relief, including participants' attempts to 'exhaust all options' and limited success in finding lasting relief. The final theme describes how pain management is complicated by living with HIV; this theme includes the influence of HIV stigma on pain communication and pain as an unwanted reminder of HIV. These data support the relevance of investigating and targeting psychosocial factors to manage neuropathic pain in HIV.
Learn More >Persistent post-traumatic headache remains a poorly understood clinical entity. Although there are currently no accepted therapies for persistent post-traumatic headache, its clinical symptoms, which primarily resemble those of migraine or tension-type headache, often serve to guide treatment. However, evidence-based justification for this treatment approach remains lacking given the paucity of knowledge regarding the characteristics of these two major persistent post-traumatic headache phenotypes and their etiology.
Learn More >To test the hypotheses that insufficient duration, high fragmentation, and poor sleep quality are temporally associated with migraine onset on the day immediately following the sleep period (day 0) and the following day (day 1).
Learn More >The mechanisms supporting bone cancer pain are incompletely understoodStress of the endoplasmic reticulum has been implicated in supporting pain in some chronic pain states WHAT THIS ARTICLE TELLS US THAT IS NEW: Using a murine model of bone cancer pain, it was observed that tumor growth was associated with the spinal production of inflammatory mediators and increased expression of endoplasmic reticulum stress markersThe pharmacologic inhibition of endoplasmic reticulum stress reduced pain-related behaviors and the production of inflammatory mediators in spinal tissue BACKGROUND:: Prolonged endoplasmic reticulum stress has been identified in various diseases. Inflammatory mediators, which have been shown to induce endoplasmic reticulum stress in several studies, have been suggested to serve as the important modulators in pain development. In this study, the authors hypothesized that the endoplasmic reticulum stress triggered by inflammatory mediators contributed to pain development.
Learn More >Conventional MRI of patients with trigeminal neuralgia (TN) does not typically reveal associated brain lesions. Here, we identify a unique group of TN patients that present with a single brainstem lesion, who do not fulfill diagnostic criteria for multiple sclerosis (MS). We aim to define this new clinical syndrome, which we term TN associated with solitary pontine lesion (SPL-TN), using a clinical and neuroimaging approach. We identified 24 cases of SPL-TN, 18 of which had clinical follow-up for assessment of treatment response. Lesion mapping was performed to determine the exact location of the lesions and site of maximum overlap across patients. Diffusion tensor imaging was used to assess the white matter microstructural properties of the lesions. Diffusivity metrics were extracted from the (1) SPL-TN lesions, (2) contralateral, unaffected side, (3) MS brainstem plaques from 17 patients with TN secondary to MS, (4) and healthy controls. We found that 17/18 patients were non-responders to surgical treatment. The lesions were uniformly located along the affected trigeminal pontine pathway, where the site of maximum overlap across patients was in the area of the trigeminal nucleus. The lesions demonstrated abnormal white matter microstructure, characterized by lower fractional anisotropy, and higher mean, radial, and axial diffusivities compared to the unaffected side. The brainstem trigeminal fiber microstructure within a lesion highlighted the difference between SPL-TN lesions and MS plaques. In conclusion, SPL-TN patients have identical clinical features to TN, but have a single pontine lesion not in keeping with MS, and are refractory to surgical management.
Learn More >The purpose of the study was to explore clinical management for new cases of musculoskeletal pain that are likely chronic. We used data from the National Ambulatory Medical Care Survey, 2007-2015, identifying visits with a new chronic musculoskeletal pain condition using pre-determined ICD-9 codes. We documented prescribing of non-opioid pain medication, opioids, physical therapy (PT), counseling, and other nonpharmacologic treatments and explored associations between patient and provider factors for each of these treatments. There were 111,994 visits over the 9-year period for a new case of chronic musculoskeletal pain, representing an average of 36.8 million weighted visits per year or approximately 11.8% of the population. Proportions that were prescribed nonopioid medication, opioids, PT, counseling and other nonpharmacologic treatments were: 40.2, 21.5, 10.0, 15.2 and 14.3 respectively. Patient age was associated with type of treatment with a young to old gradient for other nonpharmacologic treatments, PT, opioids, counseling and other medications. Orthopedists were less likely to prescribe pharmacological treatments than family practice physicians and more likely to prescribe PT. Physicians who used the electronic medical record were more likely to prescribe opioids. Contrary to practice guidelines for managing musculoskeletal pain, many patients are prescribed opioids for a new chronic musculoskeletal problem. PERSPECTIVE: We outlined in a representative sample of Americans what treatments are being prescribed for new cases of likely chronic musculoskeletal pain. Opioid prescription was double that of physical therapy. Using the electronic medical record was associated with more opioid prescription- a novel finding that should be corroborated by future research.
Learn More >Accumulating evidence suggests that epigenetic mechanisms may hold great potential in the field of pain. We systematically reviewed the literature exploring epigenetic mechanisms in people with pain. Four databases have been interrogated: MEDLINE, The Cochrane Central Register of Controlled Trial, Scopus, and Web of Science, following PRISMA guidelines in conducting study selection and assessment. Thirty-seven studies were included. Studies explored epigenetics in conditions such as fibromyalgia, CRPS, neuropathies, or osteoarthritis. Research focussed on genome-wide and gene-specific DNA methylation, and miRNA expression. Bioinformatics analyses exploring miRNA-associated molecular pathways were also performed. Several genes already known for their role in pain (BDNF, HDAC4, PRKG1, IL-17, TNFRSF13B, etc.), and several miRNAs linked to inflammatory regulation, nociceptive signalling and protein kinases functions have been found to differ significantly between people with chronic pain and healthy controls. Although the studies included were cross-sectional in nature, and no conclusion on causal links between epigenetic changes and pain could be drawn, we summarised the large amount of data available in literature on the topic, highlighting results that have been replicated by independent investigations. The field of pain epigenetics appears very exciting and has all the potential to lead to remarkable scientific advances. However, high-quality, well-powered, longitudinal studies are warranted. Perspective: Though more high-quality research is needed, available research exploring epigenetic mechanisms or miRNAs in people with pain shows that genes regulating synaptic plasticity and excitability, protein kinases, and elements of the immune system might hold great potential in understanding the pathophysiology of different conditions.
Learn More >In health and disease, the somatosensory system has been interrogated with standardized research techniques, collectively referred to as quantitative sensory testing (QST). In neuropathic pain, QST has been used to characterize multiple sensory derangements. However, the use of QST outside the lab has been limited by several factors, including a lack of standardization, variability in procedural technique, and duration of testing that would be unacceptable for clinic. To address these shortcomings, the Neuropathic Pain Research Consortium (NPRC) designed an easy and low-cost "bedside" QST procedure. To test the hypothesis that this procedure would be clinically reliable over time and across different examiners, a multi-site, blinded study was performed in subjects with postherpetic neuralgia. Generally, agreement between two examiners and over two study visits with one examiner was high. Additionally, intraclass correlation coefficients and Kappa statistics calculated showed that the battery of QST tests included were highly reliable. Interestingly, mechanical modalities (light brush, pinprick, pressure, and vibration) showed the highest reliability. The least reliable modalities were cool (room temperature) and warmth (38°C). These data demonstrate that the NPRC beside QST protocol is reliable across examiner and over time, providing a validated QST tool for use in clinical practice and clinical trials. Perspective: This blinded, multi-center trial in 32 patients with postherpetic neuralgia demonstrates bedside quantitative sensory testing is reliable and suitable as a clinical trial outcome. The novel bedside battery could be used in clinical trials or in clinical practice over time given the reliability data presented in this article.
Learn More >Chemotherapies of varying classes often cause neuropathy and debilitating chemotherapy-induced neuropathic pain sufficient to limit treatment and reduce quality of life for many patients battling cancer. There are currently no effective preventive or alleviative treatments for chemotherapy-induced neuropathic pain. Preclinical models have been developed to test candidate chemotherapy-induced neuropathic pain treatments; however, studies using these models rarely provide direct comparisons of effects of different chemotherapies or assess the degree to which chemotherapies produce clinically relevant signs of pain-depressed behavior. Male and female Sprague-Dawley rats received four injections of vehicle, paclitaxel, oxaliplatin, vincristine, or bortezomib on alternate days. Mechanical hypersensitivity, body weight, and food-maintained operant responding were evaluated before, during, and for up to 42 days after initiation of treatment. Morphine potency and effectiveness to reverse chemotherapy-induced effects were also evaluated. All four chemotherapies produced dose-dependent and sustained mechanical hypersensitivity in all rats. Vincristine and oxaliplatin produced transient weight loss and decreases in food-maintained operant responding in all rats, whereas paclitaxel and bortezomib produced lesser or no effect. At 4 weeks after treatment, operant responding was depressed only in paclitaxel-treated males. Morphine reversed mechanical hypersensitivity in all rats but failed to reverse paclitaxel-induced depression of operant responding in males. We conclude that chemotherapy treatments sufficient to produce sustained mechanical hypersensitivity failed to produce sustained or morphine-reversible behavioral depression in rats. Insofar as pain-related behavioral depression is a cardinal sign of chemotherapy-induced neuropathic pain in humans, these results challenge the presumption that these chemotherapy-dosing regimens are sufficient to model clinically relevant chemotherapy-induced neuropathic pain in rats.
Learn More >Nocebo effects encompass negative responses to inert interventions in the research setting and negative outcomes with active treatments in the clinical research or practice settings, including new or worsening symptoms and adverse events, stemming from patients' negative expectations and not the pharmacologic action of the treatment itself. Numerous personality, psychosocial, neurobiological, and contextual/environmental factors contribute to the development of nocebo effects, which can impair quality of life and reduce adherence to treatment. Biologics are effective agents widely used in autoimmune disease, but their high cost may limit access for patients. Biosimilar products have gained regulatory approval based on quality, safety, and efficacy comparable to that of originator biologics in rigorous study programs. In this review, we identified gaps in patients' and healthcare professionals' awareness, understanding, and perceptions of biosimilars that may result in negative expectations and nocebo effects, and may diminish their acceptance and clinical benefits. We also examined features of nocebo effects with biosimilar treatment that inform research and clinical practices. Namely, when biosimilars are introduced to patients as possible treatment options, we recommend adoption of nocebo-reducing strategies to avoid negative expectations, including delivery of balanced information on risk-benefit profiles, framing information to focus on positive attributes, and promoting shared decision-making processes along with patient empowerment. Healthcare professionals confident in their knowledge of biosimilars and aware of bias-inducing factors may help reduce the risk of nocebo effects and improve patients' adherence in proposing biosimilars as treatment for autoimmune diseases such as rheumatoid arthritis and inflammatory bowel disease.
Learn More >It is increasingly recognized that chronic opioid use leads to maladaptive changes in the composition and localization of gut bacteria. Recently, this "opioid-induced dysbiosis" (OID) has been linked to antinociceptive tolerance development in preclinical models and may therefore identify promising targets for new opioid-sparing strategies. Such developments are critical to curb dose escalations in the clinical setting and combat the ongoing opioid epidemic. In this article, we review the existing literature that pertains to OID, including the current evidence regarding its qualitative nature, influence on antinociceptive tolerance, and future prospects. Perspective: This article reviews the current literature on opioid-induced dysbiosis (OID) of gut bacteria, including its qualitative nature, influence on antinociceptive tolerance, and future prospects. This work may help identify targets for new opioid-sparing strategies.
Learn More >The definition of chronic migraine has long been debated. Recently, it was suggested to define subjects with at least 8/migraine days as chronic migraine; that is, incorporating so-called high frequency episodic migraine (eight or more migraine days but less than 15 headache days per month).
Learn More >The objectives of this study were to determine the rates of nausea, phonophobia, and photophobia reported overall and as the most bothersome symptom (MBS) in individuals with migraine and to identify individual characteristics associated with each of the 3 candidate MBSs.
Learn More >Pain with movement is a common issue for older adults with osteoarthritis; however, there has been insufficient attention within populations at increased risk for disabling pain, such as African American older adults. Accordingly, using a mixed methods approach, the purpose of the current study is to describe the nature of chronic joint pain and movement and its impact on physical function in African American older adults with symptomatic osteoarthritis. The authors accrued a sample of 110 African American older adults who completed cross-sectional surveys; from this sample, the authors interviewed 18 participants. Findings suggest that patterns of movement are uniquely influenced by pain. Specifically, three dynamic themes emerged: The Impact of Pain on Movement; The Importance and Impact of Movement on Pain; and The Adaptation of Personal Behaviors to Minimize Pain With Movement. Function-focused nursing care rests on addressing challenges and opportunities that African American older adults face in maintaining healthy movement when managing osteoarthritis pain. [Research in Gerontological Nursing, xx(x), xx-xx.].
Learn More >Chronic pain is highly prevalent among patients with mood, anxiety, personality, and somatic symptom disorders; and patients with chronic pain often suffer from persistent interpersonal distress. However, the neural mechanisms underlying this phenomenon and its possible role in the etiology of chronic pain are not yet understood. Based on our Developmental Theory of Centralized/Somatoform Pain, and prior research suggesting the existence of a shared neural system subserving interpersonal emotions and pain, we aimed to identify the neural basis for modulation of pain by feelings of interpersonal rejection and the role of the early interpersonal environment in development of this shared neural system.
Learn More >Persistent post-surgical pain (PPSP) is a common condition following surgery, resulting in persistent pain and reduced quality of life (QoL). While pharmacological management is common, its effectiveness remains equivocal. This systematic review investigated the effectiveness of physiotherapy management in adults with PPSP in comparison to usual care.
Learn More >Neck pain is reported in more than 50% of migraine patients during migraine attacks and may be an important source to migraine pain.
Learn More >Previous research has shown that African Americans (AA) report higher pain intensity and pain interference than other racial/ethnic groups as well as greater levels of other risk factors related to worse pain outcomes, including PTSD symptoms, pain catastrophizing, and sleep disturbance. Within a Conservation of Resources theory framework, we tested the hypothesis that socioeconomic status (SES) factors (i.e., income, education, employment, perception of income meeting basic needs) largely account for these racial/ethnic differences. Participants were 435 women [AA, 59.1%; Hispanic/Latina (HL), 25.3%; Non-Hispanic/White (NHW), 15.6%] who presented to an Emergency Department (ED) with an acute pain-related complaint. Data were extracted from psychosocial questionnaires completed at the participants' baseline interview. Structural equation modeling was used to examine whether racial/ethnic differences in pain intensity and pain interference were mediated by PTSD symptoms, pain catastrophizing, sleep quality, and sleep duration, and whether these mediation pathways were, in turn, accounted for by SES factors. Results indicated that SES factors accounted for the mediation relationships linking AA race to pain intensity via PTSD symptoms and the mediation relationships linking AA race to pain interference via PTSD symptoms, pain catastrophizing, and sleep quality. Results suggested that observed racial/ethnic differences in AA women's pain intensity, pain interference, and common risk factors for elevated pain may be largely due to racial/ethnic differences in SES. These findings highlight the role of social inequality in persistent health disparities facing inner-city, AA women.
Learn More >The non-selective activation of central and peripheral opioid receptors is a major shortcoming of currently available opioids. Targeting peripheral opioid receptors is a promising strategy to preclude side effects. Recently, we showed that fentanyl-derived μ-opioid receptor (MOR) agonists with reduced acid dissociation constants (pK) due to introducing single fluorine atoms produced injury-restricted antinociception in rat models of inflammatory, postoperative and neuropathic pain. Here, we report that a new double-fluorinated compound (FF6) and fentanyl show similar pK, MOR affinity and [S]-GTPγS binding at low and physiological pH values. In vivo, FF6 produced antinociception in injured and non-injured tissue, and induced sedation and constipation. The comparison of several fentanyl derivatives revealed a correlation between pK values and pH-dependent MOR activation, antinociception and side effects. An opioid ligand's pK value may be used as discriminating factor to design safer analgesics.
Learn More >Local microvascular dysfunction and consequent tissue ischemia/hypoxia contribute to the symptoms of complex regional pain syndrome (CRPS) and peripheral neuropathic pain. As nitric oxide (NO) is a key regulator of microvascular blood flow, compounds that increase it are potentially therapeutic for these pain conditions. This led us to hypothesize that the topical administration of drugs that modulate local tissue NO levels can alleviate the pain of CRPS and peripheral neuropathic pain. We investigated the anti-allodynic effect of a combination of two NO-modulating drugs: meldonium and N-acetylcysteine (NAC). An equimolar topical formulation of the two drugs was tested on chronic post-ischemic pain (CPIP), a rat model of CRPS, chronic constriction injury (CCI) of the sciatic nerve and chemotherapy-induced painful neuropathy (CIPN), rat models of peripheral neuropathic pain. Topical meldonium-NAC produced significant anti-allodynia in CPIP, CCI and CIPN rats. Moreover, repeated application of topical meldonium-NAC produced an increase in the duration of anti-allodynia in the CPIP and CCI rats. While pre-treatment with an NO synthase inhibitor attenuated the anti-allodynic effects of meldonium-NAC, 30-min hyperbaric oxygen treatment combined with a non-effective dose of meldonium-NAC produced significant anti-allodynic effects in CPIP rats. Both experiments implicated NO in the drug combination's anti-allodynic effects. To ascertain the role played by changes in local tissue NO, we performed a quantification of plantar muscle NO in CPIP rats after hind paw topical treatment with meldonium-NAC and revealed significantly increased plantar muscle NO levels in drug-treated rats. The drug combination also reversed the reduction in tissue oxygenation normally observed in CPIP hind paws. In addition to introducing a novel topical treatment for mechanical allodynia in CRPS and peripheral neuropathic pain, this work showcases the analgesic potential of locally targeting microvascular dysfunction and tissue ischemia/hypoxia in these conditions, with emphasis on the role of NO.
Learn More >Since the first discovery that the bioactive lipid, lysophosphatidic acid (LPA) and LPA receptor signaling play a role in the initiation of neuropathic pain (NeuP), accumulated reports have supported the original findings and extended the study toward possible therapeutic applications. The present review describes beneficial roles of LPA receptor signaling in a variety of chronic pain, such as peripheral NeuP induced by nerve injury, chemotherapy and diabetes, central NeuP induced by cerebral ischemia with hemorrhage and spinal cord injury, and fibromyalgia-like wide spread pain induced by repeated cold, psychological and muscular acidic stress. Emerging mechanistic findings are the feed-forward amplification of LPA production through LPA, LPA and microglia and the evidence for maintenance of chronic pain by LPA receptor signaling.
Learn More >In spite of the substantial therapeutic efficacy of triptans, their site of action is still debated. Subcutaneous sumatriptan is the most efficacious symptomatic treatment for cluster headache (CH) patients, showing therapeutic onset within a few minutes after injection even in migraine patients. However, whether subcutaneous sumatriptan is able to reach the CNS within this short time frame is currently unknown.
Learn More >This issue of the Clinical Journal of Pain includes a series of review articles from the international symposium "Approach to physical activity in pain: translation from theory to the lab, from the clinic to the patient" which was held as an Official Satellite Symposium of the 17 World Congress on Pain, 2018 in Boston, USA and organized by the Mind and Pain in Motion Research Group (Chair: MIH) and colleagues from the field of clinical rehabilitation in Austria (EF, GE). The symposium brought together world's leading researchers from multiple disciplines to further advance our understanding of the complex interaction of cognitive, behavioral and neuromuscular mechanisms that may play a role for the development and maintenance of chronic musculoskeletal pain. Following up on a previous Satellite Meeting 2012 in Nottwil, Switzerland and the first Mind and Pain in Motion Symposium, held 2016 at Ruhr University of Bochum, Germany, the 2018 meeting in Boston presented (1) new theoretical approaches in psychobiological pain research, (2) current experimental research in endogenous pain modulation, initiated by exercise behavior, stress and pain cognitions (3) latest findings on the phenomena of physical overactvity, endurance-related pain response pattern, neuromuscular activity and possible interrelations, and (4) clinical approaches to a more individualized, patient-oriented management in the field of musculoskeletal pain disorders.
Learn More >Increasing physical function is a challenging, yet imperative goal of pain management programs. Physical activity can improve physical function, but uptake is low due to chronic pain misconceptions, poor pain management skills, and doing too much too soon.
Learn More >A decrease in glutamate in the medial prefrontal cortex (mPFC) has been extensively found in animal models of chronic pain. Given that the mPFC is implicated in emotional appraisal, cognition and extinction of fear, could a potential decrease in glutamate be associated with increased pessimistic thinking, fear and worry symptoms commonly found in people with chronic pain? To clarify this question, 19 chronic pain subjects and 19 age- and gender-matched control subjects without pain underwent magnetic resonance spectroscopy. Both groups also completed the Temperament and Character, the Beck Depression and the State Anxiety Inventories to measure levels of harm avoidance, depression, and anxiety, respectively. People with chronic pain had significantly higher scores in harm avoidance, depression and anxiety compared to control subjects without pain. High levels of harm avoidance are characterized by excessive worry, pessimism, fear, doubt and fatigue. Individuals with chronic pain showed a significant decrease in mPFC glutamate levels compared to control subjects without pain. In people with chronic pain mPFC glutamate levels were significantly negatively correlated with harm avoidance scores. This means that the lower the concentration of glutamate in the mPFC, the greater the total scores of harm avoidance. High scores are associated with fearfulness, pessimism, and fatigue-proneness. We suggest that chronic pain, particularly the stress-induced release of glucocorticoids, induces changes in glutamate transmission in the mPFC, thereby influencing cognitive, and emotional processing. Thus, in people with chronic pain, regulation of fear, worry, negative thinking and fatigue is impaired.
Learn More >The psychoactive plant kratom is a native plant to Southeast Asia, and its major bioactive alkaloid is mitragynine. Mitragynine exerts its analgesic properties by acting on the opioid receptors. One of its active metabolites, 7-hydroxymytraginine, is found to be 40 times more potent than mitragynine and 10 times more potent than morphine. Interestingly, current research suggests that mitragynine behaves as an atypical opioid agonist – possessing analgesic activity with less severe side effects than typical opioids. Although Thailand and Malaysia have criminalized the use, possession, growing, or selling of kratom due to its abuse potential, kratom still remains unregulated in the United States. The U.S. Drug Enforcement Agency (DEA) listed kratom as a "drug of concern" in 2008 with the intent to temporarily place mitragynine and 7-hydroxymitragynine onto Schedule I of the Controlled Substances Act. However, responses from the general public, U.S. Congress, and Kratom Alliances had the DEA retract their intent. Kratom is currently marketed in the U.S. as a dietary or herbal supplement used to treat chronic pain, anxiety, and depression with over $207 million in annual sales in the U.S. alone. Here, we will review the traditional and medicinal uses of kratom along with the synthesis of its bioactive ingredients, their pharmacology, metabolism, and structure-activity relationships. The importance in society of this currently controversial substance will also be discussed.
Learn More >Safe opioid prescribing practices are critical to mitigate the risk of prescription opioid overdose in adolescents and young adults. However, studies that examine opioid prescribing patterns associated with prescription opioid overdose have mostly focused on older adults. The generalizability of these studies to adolescents and young adults is unclear.
Learn More >Grimace scales have been used for pain assessment in different species. This study aimed to develop and validate the Feline Grimace Scale (FGS) to detect naturally-occurring acute pain. Thirty-five client-owned and twenty control cats were video-recorded undisturbed in their cages in a prospective, case-control study. Painful cats received analgesic treatment and videos were repeated one hour later. Five action units (AU) were identified: ear position, orbital tightening, muzzle tension, whiskers change and head position. Four observers independently scored (0-2 for each AU) 110 images of control and painful cats. The FGS scores were higher in painful than in control cats; a very strong correlation with another validated instrument for pain assessment in cats was observed (rho = 0.86, p < 0.001) as well as good overall inter-rater reliability [ICC = 0.89 (95% CI: 0.85-0.92)], excellent intra-rater reliability (ICC > 0.91), and excellent internal consistency (Cronbach's alpha = 0.89). The FGS detected response to analgesic treatment (scores after analgesia were lower than before) and a cut-off score was determined (total pain score > 0.39 out of 1.0). The FGS is a valid and reliable tool for acute pain assessment in cats.
Learn More >Four novel fluorinated cyclic analogues of biphalin with excellent to modest binding affinity for μ-, δ- and κ-receptors were synthesized. The cyclic peptides have a combination of piperazine or hydrazine linker with or without a xylene bridge. Among the ligands, MACE3 demonstrated a better activity than biphalin after intravenous administration, and its corresponding analogue incorporating the hydrazine linker (MACE2) was able to induce longer lasting analgesia following subcutaneous administration. An analogue of MACE2 containing 2,6-dimethyl-L-tyrosine (MACE4) showed the best potency and in vivo antinociceptive activity of this series.
Learn More >Comprehensive evaluation of chronic pain in older adults is multifaceted.
Learn More >Decades of research have convincingly shown, that fear of pain and pain-related avoidance behavior are important precursors of disability in daily life. Physical underuse as a consequence of avoidance, however, cannot not be blamed for chronic disability in all patients, a contrasting behavior, pain-related dysfunctional endurance in a task and overactivity, have to be considered. Currently there is a need to better understand psychological determinants of overactivity, dysfunctional endurance and neuro-biomechanical consequences.
Learn More >Because musculoskeletal pain problems are so prevalent, new methods of evaluating and treating patients are needed to increase effectiveness. Subgrouping is a method where patients are classified into defined groups based on psychosocial factors with the expectation of more specific and tailored treatments for them. For those seeking care for a new episode, the risk of developing chronic pain-related disability is assessed, while for those with existing pain the risk for the maintenance of the chronic pain problem is evaluated. In this narrative review we examine the subgrouping of patients with regard to methods of evaluation as well as to whether subgrouping actually facilitates treatment. For the development of disability, screening tools e.g. the Örebro Musculoskeletal Pain Screening Questionnaire accurately stratify patients into group (e.g. high, medium, low risk) that predict future pain-related work disability. In addition, several studies show that treatments that directly key on risk groups enjoy enhanced outcomes compared to treatment as usual. For the maintenance of chronic musculoskeletal pain problems there are several instruments that classify patients into specific groups or profiles e.g. based on the avoidance and endurance model or the ICF assessment. While some evidence shows that these classifications are related to treatment outcome, we found no study that directly tested a system for providing treatment matched to the subgrouping for maintenance. We conclude that it is possible to reliably subgroup patients with musculoskeletal problems. Likewise, treatments that address the risk factors in the screening procedure, may enhance outcomes compared to treatment as usual. More work is needed however, to better understand mechanism so assessment methods can be improved and treatment specific to subgroups can be developed.
Learn More >Pain is a complex and highly subjective phenomenon that can be modulated by several factors. Based on results from experimental and clinical studies, the existence of endogenous pain modulatory mechanisms that can increase or diminish the experience of pain is now accepted. In this narrative review, the pain modulatory effects of exercise, stress, and cognitions in humans are assessed. Experimental studies on the effect of exercise have revealed that pain-free subjects show a hypoalgesic response after exercise. However, in some patients with chronic pain this response is reduced or even hyperalgesic in nature. These findings will be discussed from a mechanistic point of view. Stress is another modulator of the pain experience. Although acute stress may induce hypoalgesia, ongoing clinical stress has detrimental effects on pain in many patients with chronic pain conditions, which have implications for the understanding, assessment and treatment of stress in patients with pain. Finally, cognitive strategies play differing roles in pain inhibition. Two intuitive strategies, thought suppression and focused distraction, will be reviewed regarding experimental, acute, and chronic pain. Based on current knowledge on the role of exercise, stress, and cognitive pain control strategies on modulation of pain, implications for treatment will be discussed.
Learn More >The classification of chronic visceral pain is complex, resulting from persistent inflammation, vascular (ischemic) mechanisms, cancer, obstruction or distension, traction or compression, and combined mechanisms, as well as unexplained functional mechanisms. Despite the prevalence, treatment options for chronic visceral pain are limited. Given this unmet clinical need, the development of novel analgesic agents, with defined targets derived from preclinical studies, is urgently needed. While various animal models have played an important role in our understanding of visceral pain, our knowledge is far from complete. Due to the complexity of visceral pain, this document will focus on chronic abdominal pain, which is the major complaint in patients with disorders of the gut-brain interaction, also referred to as functional gastrointestinal disorders, such as irritable bowel syndrome (IBS). Models for IBS are faced with challenges including a complex clinical phenotype, which is comorbid with other conditions including anxiety, depression, painful bladder syndrome, and chronic pelvic pain. Based upon the multifactorial nature of IBS with complicated interactions between biological, psychological, and sociological variables, no single experimental model recapitulates all the symptoms of IBS. This position paper will contextualize chronic visceral pain using the example of IBS and focus on its pathophysiology while providing a critical review of current animal models that are most relevant, robust, and reliable in which to screen promising therapeutics to alleviate visceral pain and delineate the gaps and challenges with these models. We will also highlight, prioritize, and come to a consensus on the models with the highest face/construct validity.
Learn More >Central post-stroke pain (CPSP) is a neuropathic disorder resulting in pain and disability. An emerging treatment for CPSP is non-invasive brain stimulation including direct current stimulation [tDCS] and repetitive transcranial magnetic stimulation [rTMS]. This systematic review analyzes the efficacy and quality of non-invasive brain stimulation intervention studies for CPSP.
Learn More >This review sought to (a) describe definitions of long-term opioid therapy (LTOT) outcome measures, and (b) identify the predictors associated with the transition from short-term opioid use to LTOT for opioid-naïve individuals.
Learn More >Current treatment options for chronic pain and depression are largely medication-based, which may cause adverse side effects. Integrative Medical Group Visits (IMGV) combines mindfulness techniques, evidence based integrative medicine, and medical group visits, and is a promising adjunct to medications, especially for diverse underserved patients who have limited access to non-pharmacological therapies.
Learn More >Neuropathic pain is a debilitating consequence of spinal cord injury. Ecological momentary assessment can be a valuable research tool for understanding temporal fluctuations in neuropathic pain and designing effective management strategies. The objectives of this study were to (a) describe strategies necessary to adapt ecological momentary assessment to measure neuropathic pain in adults with spinal cord injury, and (b) explore participant perceptions of using ecological momentary assessment to measure pain sensations. End-users with spinal cord injury provided input to guide development of an ecological momentary assessment protocol. Six adults with spinal cord injury (ages 27-50 years, = 39.33 ± 8.24) engaged in the six-day protocol and completed six daily neuropathic pain assessments. Upon finishing participants completed a semi-structured interview regarding their protocol experiences. A qualitative content analysis was used to analyze the interview data. Participants reported that this specific ecological momentary assessment protocol was unobtrusive to their daily routines, and effectively captured their neuropathic pain sensations. However, participants experienced increased neuropathic pain due to the repeated nature of assessments. Ecological momentary assessment can capture the dynamic nature of neuropathic pain experienced by persons with spinal cord injury. However, caution should be taken when designing intensive pain-related protocols to minimize pain exacerbation.IMPLICATIONS FOR REHABILITATIONNeuropathic pain affects up to 75% of people with spinal cord injury and is one of the most frequently occurring, debilitating forms of pain.Appropriate and feasible pain data collection methods are necessary to acquire a better understanding of how neuropathic pain manifests in people with spinal cord injury.Implementing ecological momentary assessment in a rehabilitation setting may help facilitate the monitoring of neuropathic pain for both rehabilitation professionals and persons with SCI.Using ecological momentary assessment may lead to a better understanding of individual temporal patterns of neuropathic pain that could inform the design of tailored neuropathic pain management techniques.
Learn More >Chronic low back pain (CLBP) is characterized by an alteration in pain processing by the central nervous system that may affect autonomic nervous system (ANS) balance. Heart rate variability (HRV) reflects the balance of parasympathetic and sympathetic ANS activation. In particular, respiratory sinus arrhythmia (RSA) solely reflects parasympathetic input and is reduced in CLBP patients. Yet, it remains unknown if non-invasive brain stimulation can alter ANS balance in CLBP patients.
Learn More >Dry eye disease (DED) is a multifactorial disease associated with ocular surface inflammation, pain, and nerve abnormalities. We studied the peripheral and central neuroinflammatory responses that occur during persistent DED using molecular, cellular, behavioral, and electrophysiological approaches.
Learn More >Recent insights into the clinical presentation and pathophysiology of migraine aura have paved the way for new treatments for this common but frequently debilitating condition. Marked efflux of cellular potassium and glutamate contributes to the cortical spreading depression that forms the electrophysiological basis of migraine aura phenomena. Secondary vascular perturbations also contribute to the various symptoms of a migraine attack. Calcitonin gene-related peptide (CGRP) plays a key role in many of these steps, and a growing class of CGRP-antagonists have emerged as a novel, efficacious preventative therapy. It is still not fully understood why a preponderance of migraine aura symptoms is visual, and this issue is an active area of research. In addition, the pathophysiological changes responsible for visual snow syndrome are under investigation. Before diagnosing a patient with migraine aura, it is important to consider the differential diagnosis of transient visual phenomena, with attention to clinical features that may suggest conditions such as retinal disorders, transient ischemic attack, or occipital epilepsy.
Learn More >Paclitaxel (PTX) is one of the most commonly used chemotherapeutic agents for various cancer diseases. Despite its advantages, PTX also causes behavioral deficits related to nervous-system dysfunction, such as neuropathic pain, depression, anxiety, and cognitive impairments. The prefrontal cortex (PFC) is one of the areas that is susceptible to adverse effects of chemotherapeutic agents. Therefore, the present study was designed to examine sex-biased behavioral deficits and whole-transcriptome changes in gene expression in the PFC of mice treated with vehicle or PTX. In this study, PTX (4mg/kg) was injected intraperitoneally four times in mice every other day. Three weeks later, both PTX-treated male and female mice developed mechanical pain hypersensitivities, as indicated by increased paw withdrawal responses to 0.16-g von Frey filaments. Additionally, PTX-treated mice exhibited depression-like symptoms, as they exhibited increased immobility times in the forced swim test. PTX also induced cognitive impairment, as demonstrated via results of a novel object recognition test and anxiety-like behavior in an elevated plus-maze test in male mice, but not in female mice. RNA sequencing and in-depth gene expression analysis of the PFC in paired vehicle and PTX-treated mice showed that PTX induced 1,755 differentially expressed genes in the PFCs of male and female mice. Quantitative real-time RT-PCR verified that some gene expressions in the medial PFC were related to neurotransmission. In conclusion, this study identified a sex-biased effect of PTX on PFC function and gene expression, which provides a foundation for future studies to explore the precise mechanisms of PTX-induced behavioral deficits.
Learn More >Osteoarthritis (OA) is the most prevalent joint disorder associated with severe chronic pain. Although synovial inflammation is well correlated with pain severity, the molecular mechanism responsible for OA pain remains unclear. Here, we show that extracellular miR-21 released from synovial tissue mediates knee OA pain in surgical OA model rats. miR-21 was the most abundant among increased microRNAs (miRNAs) in the synovial tissue. miR-21 was released into extracellular space from the synovial tissue and increased in the synovial fluid. A single intra-articular injection of miR-21 inhibitor exerted long-term analgesia of knee OA pain, whereas miR-21 injection in naive rats caused knee joint pain. miR-21 mutant, which lacks the Toll-like receptor (TLR) binding motif, but not in the seed sequence, did not cause joint pain, suggesting a non-canonical mode of action different from translational repression. Consistent with this, the algesic effect of miR-21 was blocked by antagonizing TLR7. The TLR7 antagonist also exerted a long-lasting analgesic effect on knee OA pain. Therefore, extracellular miR-21 released from synovial tissue mediates knee OA pain through TLR7 activation in surgical OA model rats. Extracellular miRNA in the joint may be a plausible target for pain therapy, providing a novel analgesic strategy for OA.
Learn More >Small-fiber neuropathy (SFN) is a known cause for pain, however it may be also associated with chronic itch. The clinical profile of chronic itch due to SFN is poorly defined and accordingly under diagnosed in clinical care.
Learn More >The aim of this systematic review was to summarize the effects of physical exercise on neuropathic pain (NP) in animal models of SCI. The search was conducted in Medline and Science Direct to identify experimental pre-clinical studies involving animal models of SCI, physical exercise as an intervention and the assessment of NP. Fifteen articles met the eligibility criteria. The review shows that in studies of NP involving animal models of SCI, rodents are the most common species. Thoracic contusion is the most common injury and mechanical and thermal nociception are the most frequently assessed NP components. The benefits of physical exercise vary according to its starting period and total duration. In addition, there is considerable heterogeneity regarding the type and intensity of exercise capable of alleviating NP after SCI. Furthermore, physical exercise has beneficial effects on mechanical, thermal and cold nociception, and spontaneous pain. These results are weakened by the paucity of studies involving these pain outcomes. The review protocol is published for free access on the SyRF platform (http://syrf.org.uk/protocols/).
Learn More >Functional-anatomical changes in reward related brain circuits are described in chronic pain patients who report anhedonia or depressed mood. In pre-clinical rodent models of neuropathic pain there are varying reports of the effects of nerve injury on the motivation to consume sucrose, although hedonic responses to sucrose appear unchanged. These observations are derived from brief periods of exposure to sucrose. When sucrose is available ad libitum over a period of 21 days, there are marked individual differences in consumption. The motivation for, and hedonic experience of, drinking sucrose is mediated in part by dopamine-D2 and µ-opioid receptors in the nucleus accumbens (NAc). This study investigated the effects of chronic constriction injury (CCI) on ad libitum sucrose consumption in male Sprague Dawley rats and the expression of accumbal dopamine D2 and µ-opioid receptors. Nerve injury reduced sucrose drinking predominantly in rats with the highest pre-injury consumption levels. Despite these reductions in consumption, sucrose preferences were stable. In the NAc of rats whose sucrose consumption was affected by CCI, immunohistochemical analyses revealed bilateral reductions of dopamine D2-receptor expression in the core and shell; and a lateralised reduction of µ-opioid receptor expression in the core and dorsomedial shell of the right NAc. These alterations in receptor expression are located in regions which have been identified as hedonic hot and coldspots along an affective-motivational keyboard which directs behaviours either towards, or away from salient stimuli. These changes likely underlie the reduction in sucrose consumption observed in a subgroup of rats following nerve injury.
Learn More >Tonic spinal cord stimulation (SCS) is currently used to treat neuropathic pain. With this type of stimulation, an implantable pulse generator generates electrical paresthesias in the affected area through one or more epidural leads. The goal of this study was to evaluate the impact of tonic SCS on the sensory perception of chronic pain patients using quantitative sensory testing (QST).
Learn More >To present the clinical picture, the associated complications and the genetic findings of Jordanian patients diagnosed with Congenital insensitivity to pain with anhidrosis (CIPA).
Learn More >The aim of this study was to examine the inhibitory effect of teriparatide (TPTD) on pain and on bone loss in ovariectomized (OVX) mice. The mechanism of osteoporotic pain in OVX mice was evaluated through an examination of pain-related behavior as well as immunohistochemical examinations.
Learn More >To identify the role of age and gender in analgesic and adverse effects after administering fentanyl products for breakthrough pain (BT), given in doses proportional to opioid doses given for background pain.
Learn More >RA flares are common and disabling. They are described in terms of worsening inflammation but pain and inflammation are often discordant. To inform treatment decisions, we investigated whether inflammatory and pain flares are discrete entities.
Learn More >SAR studies of a reported menthol-based TRPM8 antagonist, guided by computational simulations and structure-based design, uncovers a novel series of TRPM8 antagonists with >10-fold selectivity versus related TRP subtypes. Spiro[4.5]decan-8-yl analog 14 inhibits icilin-evoked Ca2+ entry in HEK-293 cells stably expressing human TRPM8 (hTRPM8) with an IC50: 2.4 ± 1.0 nM, while in whole-cell patch-clamp recordings, this analog inhibits menthol-evoked currents with an hTRPM8 IC50: 64 ± 2 nM. Molecular dynamics (MD) simulations of compound 14 in our homology model of hTRPM8 suggests that this antagonist forms extensive hydrophobic contacts within the orthosteric site. In the wet dog shakes (WDS) assay, compound 14 dose-dependently blocks icilin-triggered shaking behaviors in mice. Upon local administration, compound 14 dose dependently inhibits cold allodynia evoked by the chemotherapy oxaliplatin in a murine model of peripheral neuropathy at microgram doses. Our findings suggest that 14 and other biphenyl amide analogs within our series can find utility as potent antagonist chemical probes derived from (-)-menthol, as well as small molecule therapeutic scaffolds for chemotherapy-induced peripheral neuropathy (CIPN) and other sensory neuropathies.
Learn More >Human brain imaging studies have revealed several regions that are activated in patients with chronic pain. In rodent brains, functional changes due to chronic pain have not been fully elucidated, as brain imaging techniques such as functional magnetic resonance imaging and positron emission tomography (PET) require the use of anesthesia to suppress movement. Consequently, conclusions derived from existing imaging studies in rodents may not accurately reflect brain activity under awake conditions. In this study, we used quantitative activation-induced manganese-enhanced magnetic resonance imaging to directly capture the previous brain activity of awake mice. We also observed and quantified the brain activity of the spared nerve injury (SNI) neuropathic pain model during awake conditions. SNI-operated mice exhibited a robust decrease of mechanical nociceptive threshold 14 days after nerve injury. Imaging on SNI-operated mice revealed increased neural activity in the limbic system and secondary somatosensory, sensory-motor, piriform, and insular cortex. We present the first study demonstrating a direct measurement of awake neural activity in a neuropathic pain mouse model.
Learn More >The actions of caffeine as an antagonist of adenosine receptors have been extensively studied, and there is no doubt that both daily and sporadic dietary consumption of caffeine has substantial biological effects on the nervous system. Caffeine influences headaches, the migraine syndrome in particular, but how is unclear. This is a narrative review based on selected articles from an extensive literature search. The aim of this study is to elucidate and discuss how caffeine may affect the migraine syndrome and discuss the potential pathophysiological pathways involved. Whether caffeine has any significant analgesic and/or prophylactic effect in migraine remains elusive. Neither is it clear whether caffeine withdrawal is an important trigger for migraine. However, withdrawal after chronic exposure of caffeine may cause migraine-like headache and a syndrome similar to that experienced in the prodromal phase of migraine. Sensory hypersensitivity however, does not seem to be a part of the caffeine withdrawal syndrome. Whether it is among migraineurs is unknown. From a modern viewpoint, the traditional vascular explanation of the withdrawal headache is too simplistic and partly not conceivable. Peripheral mechanisms can hardly explain prodromal symptoms and non-headache withdrawal symptoms. Several lines of evidence point at the hypothalamus as a locus where pivotal actions take place. In general, chronic consumption of caffeine seems to increase the burden of migraine, but a protective effect as an acute treatment or in severely affected patients cannot be excluded. Future clinical trials should explore the relationship between caffeine withdrawal and migraine, and investigate the effects of long-term elimination.
Learn More >Migraine is a debilitating primary headache disorder with a poorly understood aetiology. An extensive body of literature supports the theory of migraine as a systemic vascular inflammatory disorder characterised by endothelial dysfunction. It is also well-known that chronic inflammation results in an excessive burden of oxidative stress and therefore cellular dysfunction. In this study the effects of excessive oxidative stress through the phases of female migraine-with-aura (FMA) were evaluated by examining the health of the systems of haemostasis. Blood was obtained from 11 FMA patients at baseline and during the headache phase of migraine, as well as from 8 healthy age-matched female controls. Samples were analysed using thromboelastography (TEG) to evaluate viscoelastic profiles, light microscopy for erythrocyte morphology, Scanning Electron Microscopy (SEM) for erythrocyte and fibrin clot structure, confocal microscopy for β-amyloid detection in fibrin clots. Viscoelastic profiles from platelet poor plasma showed decreased clot reaction times in FMA at baseline (95% CI [5.56, 8.41]) vs. control (95% CI [7.22, 11.68]); as well as decreased time to maximum thrombus generation for the same comparison (95% CI [6.78, 10.20] vs. [8.90, 12.96]). Morphological analysis of erythrocytes indicated widespread macrocytosis, poikilocytosis and eryptosis in the migraineurs. Analysis of fibrin networks indicated that this hypercoagulability may be a result of aberrant fibrin polymerisation kinetics caused by the adoption of a β-amyloid conformation of fibrin(ogen). The results reaffirm the hypercoagulable state in migraine, and would suggest that this state is most likely a result of a systemic inflammatory state which induces oxidative damage to both erythrocytes and fibrin(ogen) in female episodic migraine-with-aura. Furthermore, if the amylodogenic changes to fibrin(ogen) were observed in a larger cohort, this would support theories of micro-embolisation in migraine-with-aura.
Learn More >Neuropathic pain is one of the most debilitating of all chronic pain syndromes. Intrathecal (i.t.) bone marrow stromal cell (BMSC) injections have a favorable safety profile; however, results have been inconsistent, and complete understanding of how BMSCs affect neuropathic pain remains elusive.
Learn More >Chronic lower back pain (CLBP) is a major health care burden and often results in workplace absenteeism. It is a priority for appropriate management of CLBP to get individuals back to work as early as possible. Interventions informed by the flags approach, which integrates cognitive and behavioral approaches via identification of biopsychosocial barriers to recovery, have resulted in reduced pain-related work absences and increased return to work for individuals with CLBP. However, research indicates that physicians' adherence to biopsychosocial guidelines is low.
Learn More >i) To analyze the association of body mass index (BMI) and some serum tissue damage markers with postoperative pain. ii) To establish a biochemical marker cutoff point able to predict moderate to severe postoperative pain.
Learn More >Orexin-A is known to induce anti-nociceptive effects in animal models of chronic pain. We have found that orexin-A inhibits KCl loading-induced increases in the intracellular calcium ion levels ([Ca ] ) in C-fiber-like neurons of rats showing inflammatory nociceptive behavior. Here, we examined the effects of orexin-A on the depolarization of C-fiber-like neurons derived from a rat model for another type of chronic pain, namely neuropathic pain. Thus, we analyzed the effects of orexin-A on KCl-induced increases in [Ca ] in C-fiber-like neurons of rats with sciatic nerve ligation.
Learn More >Many single nucleotide polymorphisms (SNPs) have been reported to be associated with migraine susceptibility. However, evidences for their associations with migraine endophenotypes or subtypes are scarce. We aimed to investigate the associations of pre-identified migraine susceptibility loci in Taiwanese with migraine endophenotypes or subtypes, including chronic migraine and allodynia.
Learn More >Oxaliplatin is a widely used chemotherapeutic drug and represents the cornerstone of colorectal cancer therapy, in combination with 5-fluorouracil and folinic acid. As with many chemotherapeutic agents, its use is associated with a number of side effects, ranging from hypersensitivity reactions to haematological dyscrasias. Oxaliplatin also induces acute and chronic peripheral neuropathy. While it is likely that the haematological side effects are associated with its anti-proliferative effects and with the ability to form DNA adducts, the molecular mechanisms underlying peripheral neuropathy and hypersensitivity reactions are poorly understood, and therefore the choice of adequate supportive therapies is largely empirical. Here we show that an acute low dose oxaliplatin application on DRG neurons is able to induce an increase in intracellular calcium that is dependent on the Histamine 1 receptor (H1). Oxaliplatin-induced intracellular calcium rises are blocked by two selective H1 antagonist, as well as by U73122, a PLC inhibitor, and by 2-APB, a non-specific IP receptor blocker. Moreover, expression of the H1 receptor on HEK293 t cells unmasks an oxaliplatin-induced Ca-rise. Last, activation of H1 via either histamine or oxaliplatin activates TRPV1 receptors, a mechanism that has been associated with itch. These data, together with literature data that has shown that anti-histamine agents reduce the incidence of oxaliplatin-induced hypersensitivity, may provide a molecular mechanism of this side effect in oncological patients.
Learn More >The opioid-related behaviours in treatment (ORBIT) scale are a measure of recent indicators of potential extra-medical opioid use. Indicators of potential extra-medical opioid use are divergent practices among people prescribed opioids that may place them at risk of harm. This study aimed to examine the correlates of indicators of potential extra-medical opioid use in people prescribed opioids for chronic non-cancer pain (CNCP).
Learn More >Provoked vestibulodynia (PVD) is a chronic vulvo-vaginal pain condition affecting 8% of premenopausal women. Cognitive-behavioral therapy (CBT) is effective in managing pain and associated sexual and psychological symptoms, and a recent study found group mindfulness-based cognitive therapy (MBCT) to be equivalent. Our goal was to examine the long-term outcomes of these treatments and to explore mediators of change.
Learn More >Alcohol use disorder (AUD) and chronic pain are enduring and devastating conditions that share an intersecting epidemiology and neurobiology. Chronic alcohol use itself can produce a characteristic painful neuropathy, while the regular analgesic use of alcohol in the context of nociceptive sensitization and heightened affective pain sensitivity may promote negative reinforcement mechanisms that underlie AUD maintenance and progression. The goal of this review is to provide a broad translational framework that communicates research findings spanning preclinical and clinical studies, including a review of genetic, molecular, behavioral, and social mechanisms that facilitate interactions between persistent pain and alcohol use. We also consider recent evidence that will shape future investigations into novel treatment mechanisms for pain in individuals suffering from AUD.
Learn More >Chronic pain is a highly prevalent and debilitating condition, and there is a pressing need to find safe, effective and affordable treatments to tackle this public health issue. This pilot study aimed to assess whether therapeutic exercises supplemented by transcutaneous electrical nerve stimulation induces a greater hypoalgesic effect than therapeutic exercises supplemented by sham transcutaneous electrical nerve stimulation, in an elderly population suffering from chronic pain. Eighteen elderly participants suffering from chronic pain completed a therapeutic exercise program consisting of 45-min group sessions administered twice a week for 4 weeks. Half of the participants received real transcutaneous electrical nerve stimulation during the exercise sessions, while the others received sham transcutaneous electrical nerve stimulation. Participants completed pain questionnaires (McGill Pain Questionnaire, Brief Pain Inventory, Beck Depression Index) before and after the intervention, and recorded their pain levels on an 11-point numerical rating scale before and after each session (Clinical Trial.Gov ID: NCT02445677). Our results suggest that supplementing exercise sessions with transcutaneous electrical nerve stimulation does not improve the long-term outcomes of elderly patients suffering from chronic pain, but does induce short-term hypoalgesia during exercise sessions. Our study also offers valuable guidelines for the implementation of a future and adequately powered study looking at this research question.Implications for rehabilitationThe application of transcutaneous electrical nerve stimulation during exercises is well tolerated by elderly individuals suffering from chronic pain.Supplementing exercises with transcutaneous electrical nerve stimulation does not seem to improve general outcome in elderly suffering from chronic pain.Notwithstanding, the addition of transcutaneous electrical nerve stimulation tends to produce a marked hypoalgesic effect during the exercise sessions, an effect that could prompt indirect benefits for pain patients.
Learn More >Fibromyalgia (FM) is a disease characterized by chronic widespread pain, fatigue, aches, joint stiffness, depression, cognitive dysfunction and non-restorative sleep. In FM, neurotransmission and glial activation can occur with an increase in inflammatory cytokines and involvement of mast cells (MCs) in the skin. FM skin biopsies show an increased number of MCs, as well as the production of corticotropin releasing hormone (CRH) and substance P (SP) by the neurons, which in turn activate MCs to release neurosensitizing pro-inflammatory substances, such as cytokines, secreted preformed mediators and lipids, which can exacerbate low-grade inflammation. In fact, certain pro-inflammatory cytokines are higher in FM and mediate muscle pain, the mechanism of which is not yet clear. MC-derived tumor necrosis factor (TNF) induces nerve growth factor (NGF) and participates in nerve fiber elongation in skin hypersensitivity. IL-37 is an inhibitor of pro-inflammatory IL-1 family members which are generated and released by MCs. The goal of this article is to demonstrate that inflammatory cytokines and MC products play a role in fibromyalgia and that inflammation may be inhibited by IL-37. Here, we propose IL-37 as a cytokine that contributes to improve the pathogenesis of FM by blocking IL-1 family members. This article is protected by copyright. All rights reserved.
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