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Papers: 9 Mar 2019 - 15 Mar 2019

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Active immunisation targeting nerve growth factor attenuates chronic pain behaviour in murine osteoarthritis.

Nerve growth factor (NGF) has emerged as a key driver of pain in osteoarthritis (OA) and antibodies to NGF are potent analgesics in human disease. Here, we validate a novel vaccine strategy to generate anti-NGF antibodies for reversal of pain behaviour in a surgical model of OA.

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Kappa Opioid Receptors Drive a Tonic Aversive Component of Chronic Pain.

Pain is a multidimensional experience and negative affect, or how much the pain is "bothersome", significantly impacts the sufferers' quality of life. It is well established that the kappa opioid system contributes to depressive and dysphoric states, but whether this system contributes to the negative affect precipitated by the occurrence of chronic pain remains tenuous. Using a model of persistent pain, we show by quantitative RT-PCR, florescence hybridization, western blotting and GTPgS autoradiography an upregulation of expression and the function of kappa opioid receptors (KORs) and its endogenous ligand dynorphin in the mesolimbic circuitry in animals with chronic pain compared to surgical controls. Using microdialysis and microinjection of drugs into the mesolimbic dopamine system, we demonstrate that inhibiting KORs reinstates evoked dopamine release and reward related behaviors in chronic pain animals. Chronic pain enhanced KOR agonist-induced place aversion in a sex-dependent manner. Using various place preference paradigms, we show that activation of KORs drives pain aversive states in male but not female mice. However, KOR antagonist treatment was effective in alleviating anxiogenic and depressive affective-like behaviors in both sexes. Finally, ablation of KORs from dopamine neurons using AAV-TH-cre in KOR mice prevented pain-induced aversive states as measured by place aversion assays. Our results strongly support the use of KOR antagonists as therapeutic adjuvants to alleviate the emotional, tonic-aversive component of chronic pain, which is argued to be the most significant component of the pain experience that impacts patients' quality of life.We show that KORs are sufficient to drive the tonic-aversive component of chronic pain – the emotional component of pain that is argued to significantly impact a patient's quality of life. The impact of our study is broadly relevant to affective disorders associated with disruption of reward circuitry and thus likely contributes to many of the devastating sequelae of chronic pain, including the poor response to treatment of many patients, debilitating affective disorders (other disorders including anxiety and depression that demonstrate high co-morbidity with chronic pain) and substance abuse. Indeed, co-existing psychopathology increases pain intensity, pain-related disability and effectiveness of treatments (Jamison and Edwards, 2013).

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An NPY Y1 receptor antagonist unmasks latent sensitization and reveals the contribution of Protein Kinase A and EPAC to chronic inflammatory pain.

Peripheral inflammation produces a long-lasting latent sensitization of spinal nociceptive neurons that is masked by tonic inhibitory controls. We explored mechanisms of latent sensitization with an established four-step approach: 1) induction of inflammation; 2) allow pain hypersensitivity to resolve; 3) interrogate latent sensitization with a channel blocker, mutant mouse, or receptor antagonist; 4) disrupt compensatory inhibition with a receptor antagonist so as to reinstate pain hypersensitivity. We found that the neuropeptide Y Y1 receptor antagonist BIBO3304 reinstated pain hypersensitivity, indicative of an unmasking of latent sensitization. BIBO3304-evoked reinstatement was not observed in AC1 knockout mice and was prevented with intrathecal co-administration of a pharmacological blocker to either: the N-methyl-D-aspartate receptor (NMDAR); adenylyl cyclase type 1 (AC1); protein kinase A (PKA); transient receptor potential cation channel A1 (TRPA1); channel V1 (TRPV1); or exchange protein activated by cAMP (Epac1 or Epac2). A PKA activator evoked both pain reinstatement and touch-evoked pERK expression in dorsal horn; the former was prevented with intrathecal co-administration of a TRPA1 or TRPV1 blocker. An Epac activator also evoked pain reinstatement and pERK expression. We conclude that PKA and Epac are sufficient to maintain long-lasting latent sensitization of dorsal horn neurons that is kept in remission by the NPY-Y1 receptor system. Furthermore, we have identified and characterized two novel molecular signaling pathways in the dorsal horn that drive latent sensitization in the setting of chronic inflammatory pain: NMDAR→AC1→PKA→TRPA1/V1 and NMDAR→AC1→Epac1/2. New treatments for chronic inflammatory pain might either increase endogenous NPY analgesia or inhibit AC1, PKA or Epac.

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Benefits and harms of spinal manipulative therapy for the treatment of chronic low back pain: systematic review and meta-analysis of randomised controlled trials.

To assess the benefits and harms of spinal manipulative therapy (SMT) for the treatment of chronic low back pain.

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Kappa Opioid Signaling in the Right Central Amygdala Causes Hindpaw Specific Loss of Diffuse Noxious Inhibitory Controls (DNIC) in Experimental Neuropathic Pain.

Diffuse noxious inhibitory controls (DNIC) is a pain inhibits pain phenomenon demonstrated in humans and animals. DNIC is diminished in many chronic pain states, including neuropathic pain. The efficiency of DNIC has been suggested to prospectively predict both the likelihood of pain chronification and treatment response. Little is known as to why DNIC is dysfunctional in neuropathic pain. Here, we evaluated DNIC in the rat L5/L6 spinal nerve ligation (SNL) model of chronic pain using both behavioral and electrophysiological outcomes. For behavior, nociceptive thresholds were determined using response to noxious paw pressure on both hindpaws as the test stimulus before, and after, injection of a conditioning stimulus of capsaicin into the left forepaw. Functionally, the spike firing of spinal wide dynamic range (WDR) neuronal activity was evaluated before and during noxious ear pinch, whilst stimulating the ipsilateral paw with von Frey hairs of increased bending force. In both assays, the DNIC response was significantly diminished in the ipsilateral (i.e., injured) paw of SNL animals. However, behavioral loss of DNIC was not observed on the contralateral (i.e., uninjured) paw. Systemic application of nor-Binaltorphimine (nor-BNI), a kappa opioid antagonist, did not ameliorate SNL-induced hyperalgesia but reversed loss of the behavioral DNIC response. Microinjection of nor-BNI into the right central amygdala (RCeA) of SNL rats did not affect baseline thresholds but restored DNIC both behaviorally and electrophysiologically. Cumulatively, these data suggest that net enhanced descending facilitations may be mediated by kappa opioid receptor signaling from the RCeA to promote diminished DNIC following neuropathy.

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The unique role of the trigeminal autonomic reflex and its modulation in primary headache disorders.

The trigeminal autonomic reflex is a physiological reflex with an important protective function which also plays a role in pathophysiological conditions, such as primary headache. It is not understood whether the autonomic symptoms in trigeminal autonomic cephalalgias and migraine are the consequence of severe trigeminal discharge or indeed directly driven by central generators as part of the pathophysiology, underlying these syndromes.

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Association of Tramadol With All-Cause Mortality Among Patients With Osteoarthritis.

An American Academy of Orthopaedic Surgeons guideline recommends tramadol for patients with knee osteoarthritis, and an American College of Rheumatology guideline conditionally recommends tramadol as first-line therapy for patients with knee osteoarthritis, along with nonsteroidal anti-inflammatory drugs.

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Magi-1 scaffolds Na1.8 and Slack K channels in dorsal root ganglion neurons regulating excitability and pain.

Voltage-dependent sodium (Na) 1.8 channels regulate action potential generation in nociceptive neurons, identifying them as putative analgesic targets. Here, we show that Na1.8 channel plasma membrane localization, retention, and stability occur through a direct interaction with the postsynaptic density-95/discs large/zonula occludens-1-and WW domain-containing scaffold protein called membrane-associated guanylate kinase with inverted orientation (Magi)-1. The neurophysiological roles of Magi-1 are largely unknown, but we found that dorsal root ganglion (DRG)-specific knockdown of Magi-1 attenuated thermal nociception and acute inflammatory pain and produced deficits in Na1.8 protein expression. A competing cell-penetrating peptide mimetic derived from the Na1.8 WW binding motif decreased sodium currents, reduced Na1.8 protein expression, and produced hypoexcitability. Remarkably, a phosphorylated variant of the very same peptide caused an opposing increase in Na1.8 surface expression and repetitive firing. Likewise, in vivo, the peptides produced diverging effects on nocifensive behavior. Additionally, we found that Magi-1 bound to sequence like a calcium-activated potassium channel sodium-activated (Slack) potassium channels, demonstrating macrocomplexing with Na1.8 channels. Taken together, these findings emphasize Magi-1 as an essential scaffold for ion transport in DRG neurons and a central player in pain.-Pryce, K. D., Powell, R., Agwa, D., Evely, K. M., Sheehan, G. D., Nip, A., Tomasello, D. L., Gururaj, S., Bhattacharjee, A. Magi-1 scaffolds Na1.8 and Slack K channels in dorsal root ganglion neurons regulating excitability and pain.

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Birth experience in newborn infants is associated with changes in nociceptive sensitivity.

Vaginal birth prepares the fetus for postnatal life. It confers respiratory, cardiovascular and homeostatic advantages to the newborn infant compared with elective cesarean section, and is reported to provide neonatal analgesia. We hypothesize that infants born by vaginal delivery will show lower noxious-evoked brain activity a few hours after birth compared to those born by elective cesarean section. In the first few hours of neonatal life, we record electrophysiological measures of noxious-evoked brain activity following the application of a mildly noxious experimental stimulus in 41 infants born by either vaginal delivery or by elective cesarean section. We demonstrate that noxious-evoked brain activity is related to the mode of delivery and significantly lower in infants born by vaginal delivery compared with those born by elective cesarean section. Furthermore, we found that the magnitude of noxious-evoked brain activity is inversely correlated with fetal copeptin production, a surrogate marker of vasopressin, and dependent on the experience of birth-related distress. This suggests that nociceptive sensitivity in the first few hours of postnatal life is influenced by birth experience and endogenous hormonal production.

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Sex differences in the contributions of spinal atypical PKCs and downstream targets to the maintenance of nociceptive sensitization.

Chronic pain has been shown to depend on nociceptive sensitization in the spinal cord, and while multiple mechanisms involved in the initiation of plastic changes have been established, the molecular targets which maintain spinal nociceptive sensitization are still largely unknown. Building upon the established neurobiology underlying the maintenance of LTP in the hippocampus, this present study investigated the contributions of spinal atypical PKC isoforms PKCι/λ and PKM and their downstream targets (p62/GluA1 and NSF/GluA2 interactions, respectively) to the maintenance of spinal nociceptive sensitization in male and female rats. Pharmacological inhibition of atypical PKCs by ZIP reversed established allodynia produced by repeated intramuscular (i.m.) acidic saline injections in male animals only, replicating previously demonstrated sex differences. Inhibition of both PKCι/λ and downstream substrates p62/GluA1 resulted in male-specific reversals of i.m. acidic saline-induced allodynia, while female animals continued to display allodynia. Inhibition of NSF/GluA2, the downstream target to PKM, reversed allodynia induced by i.m. acidic saline in both sexes. Neither PKCι/λ, p62/GluA1 or NSF/GluA2 inhibition had any effect on formalin response for either sex.This study provides novel behavioural evidence for the male-specific role of PKCι/λ and downstream target p62/GluA1, highlighting the potential influence of ongoing afferent input. The sexually divergent pathways underlying persistent pain are shown here to converge at the interaction between NSF and the GluR2 subunit of the AMPA receptor. Though this interaction is thought to be downstream of PKM in males, these findings and previous work suggest that females may rely on a factor independent of atypical PKCs for the maintenance of spinal nociceptive sensitization.

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Development of a claims-based algorithm to identify potentially undiagnosed chronic migraine patients.

To develop a claims-based algorithm to identify undiagnosed chronic migraine among patients enrolled in a healthcare system.

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A conserved morphogenetic mechanism for epidermal ensheathment of nociceptive sensory neurites.

Interactions between epithelial cells and neurons influence a range of sensory modalities including taste, touch, and smell. Vertebrate and invertebrate epidermal cells ensheath peripheral arbors of somatosensory neurons, including nociceptors, yet the developmental origins and functional roles of this ensheathment are largely unknown. Here, we describe an evolutionarily conserved morphogenetic mechanism for epidermal ensheathment of somatosensory neurites. We found that somatosensory neurons in and zebrafish induce formation of epidermal sheaths, which wrap neurites of different types of neurons to different extents. Neurites induce formation of plasma membrane phosphatidylinositol 4,5-bisphosphate microdomains at nascent sheaths, followed by a filamentous actin network, and recruitment of junctional proteins that likely form autotypic junctions to seal sheaths. Finally, blocking epidermal sheath formation destabilized dendrite branches and reduced nociceptive sensitivity in . Epidermal somatosensory neurite ensheathment is thus a deeply conserved cellular process that contributes to the morphogenesis and function of nociceptive sensory neurons.

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Calcitonin-gene related peptide and disease activity in cluster headache.

To investigate the role of calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) and vasoactive intestinal polypeptide in cluster headache, we measured these vasoactive peptides interictally and during experimentally induced cluster headache attacks.

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Are signs of central sensitisation in acute low back pain a precursor to poor outcome?

Central sensitisation is considered to have a pathophysiological role in chronic low back pain (LBP). Whether individuals with increased central sensitisation early in their condition are more likely to develop persistent pain or whether it increases over time is unclear. This study aimed to determine whether sensory profiles during acute LBP differ between individuals who did and did not recover by 6-months and to identify subgroups associated with outcomes. Individuals with acute LBP (<2 weeks of onset, N=99) underwent pain threshold (heat/cold/pressure) and conditioned pain modulation (CPM) testing after completing questionnaires related to pain/disability, sleep, and psychological status. Sensory measures were compared during the acute phase (baseline) and longitudinally (baseline/6-months) between unrecovered (≥pain and disability), partially recovered (<pain and/or disability), and recovered (no pain and disability) participants at 6-months. We assessed baseline patterns of sensory sensitivity alone, and with psychological and sleep data, using hierarchical clustering and related the clusters to outcome (pain/disability) at 3- and 6-months. No sensory measure at either time-point differed between groups. Two subgroups were identified that associated with more ("high sensitivity") or less ("high sensitivity and negative psychological state") recovery. These data appear to suggest that central sensitisation during the acute-phase resolves for many, but is a precursor to the transition to chronicity when combined with other psychological features. Perspective: Central sensitisation signs during early-acute low back pain does not necessarily precede poor outcome, but may be sustained in conjunction with other psychological factors and facilitate pain persistence.

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Lack of antinociceptive cross-tolerance with co-administration of morphine and fentanyl into the periaqueductal gray of male Sprague-Dawley rats.

Tolerance to the antinociceptive effect of mu-opioid receptor (MOPr) agonists, such as morphine and fentanyl, greatly limits their effectiveness for long-term use to treat pain. Clinical studies have shown that combination therapy and opioid rotation can be used to enhance opioid-induced antinociception once tolerance has developed. The mechanism and brain regions involved in these processes are unknown. The purpose of this study was to evaluate the contribution of the ventrolateral periaqueductal gray (vlPAG) to antinociceptive tolerance and cross-tolerance between administration and co-administration of morphine and fentanyl. Tolerance was induced by pretreating rats with morphine or fentanyl or low-dose combination of morphine and fentanyl into the vlPAG followed by assessment of cross-tolerance to the other opioid. In addition, tolerance to the combined treatment was assessed. Cross-tolerance did not develop between repeated vlPAG microinjections of morphine and fentanyl. Likewise, there was no evidence of cross-tolerance from morphine or fentanyl to co-administration of morphine and fentanyl. Co-administration did not cause cross-tolerance to fentanyl. Cross-tolerance was only evident to morphine or morphine and fentanyl combined in rats pretreated with co-administration of low-doses of morphine and fentanyl. In conclusion, cross-tolerance does not develop between morphine and fentanyl within the vlPAG. This finding is consistent with the functionally selective signaling that has been reported for antinociception and tolerance following morphine and fentanyl binding to the MOPr. This research supports the notion that combination therapy and opioid rotation may be useful clinical practices to reduce opioid tolerance and other side effects. Perspective: This preclinical study shows that there is a reduction in cross tolerance between morphine and fentanyl within the periaqueductal gray which is key brain region in opioid antinociception and tolerance.

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Invited Commentary on Preventive Anti-Migraine Therapy (PAMT).

Migraine is a chronic paroxysmal neurological disorder characterized by multiphase attacks of head pain and a myriad of neurological symptoms. Chronic migraine causes a great personal and societal burden. Many patients are poorly responsive to, or non-compliant with, conventional migraine preventive therapies. For this reason, physicians are constantly looking for effective migraine prevention strategies. The recent introduction of an innovative pharmacological class useful for migraine prevention, namely monoclonal antibodies towards calcitonin gene-related peptide or its receptors, opens a new, immense therapeutic scenario. In this commentary, the development and efficacy of this novel class of preventive anti-migraine therapy have been discussed and compared with the conventional therapies of migraine prevention.

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The vast potential of claims data to reduce undiagnosed chronic migraine.

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Modulating pain thresholds through classical conditioning.

Classical conditioning has frequently been shown to be capable of evoking fear of pain and avoidance behavior in the context of chronic pain. However, whether pain itself can be conditioned has rarely been investigated and remains a matter of debate. Therefore, the present study investigated whether pain threshold ratings can be modified by the presence of conditioned non-nociceptive sensory stimuli in healthy participant.

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The Effect of Low-Carbohydrate and Low-Fat Diets on Pain in Individuals with Knee Osteoarthritis.

Osteoarthritis is the most prominent form of arthritis, affecting approximately 15% of the population in the United States. Knee osteoarthritis (KOA) has become one of the leading causes of disability in older adults. Besides knee replacement, there are no curative treatments for KOA, so persistent pain is commonly treated with opioids, acetaminophen, and nonsteroidal anti-inflammatory drugs. However, these drugs have many unpleasant side effects, so there is a need for alternative forms of pain management. We sought to test the efficacy of a dietary intervention to reduce KOA.

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Chronic pain syndromes: overlapping phenotypes with common mechanisms.

The common chronic pain syndromes of fibromyalgia, regional pain syndrome, and complex regional pain syndrome have been made to appear separate because they have been historically described by different groups and with different criteria, but they are really phenotypically accented expressions of the same processes triggered by emotional distress and filtered or modified by genetics, psychology, and local physical factors.

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The effect of guideline implementation on discharge analgesia prescribing (two years on).

The provision of appropriate discharge analgesia can be challenging and is often prescribed by some of the most junior members of the medical team. Opioid abuse has been considered a growing public health crisis and physician overprescribing is a major contributor. In 2015 an initial audit of discharge analgesia at the Royal Perth Hospital led to the development of discharge analgesia guidelines. Compliance with these guidelines was assessed by a follow-up audit in 2016, which showed improved practice. This audit assesses discharge analgesia prescribing practices two years following guideline implementation. Dispensing data were obtained for analgesic medication over a three-month period from April to July 2017 and 100 unique patients were chosen using computer generated randomisation. Patients' medical records were assessed against the hospital's Postoperative Inpatients Discharge Analgesia Guidelines. The data collected were then compared with equivalent data from the previous 2015 and 2016 audits. Overall 83.4% of the 170 discharge analgesia prescriptions written were compliant with guidelines. The highest overall compliance rates were achieved for paracetamol (100%, up from 95.9% in 2016), celecoxib (96%, down from 100% in 2016), and oxycodone immediate release (IR) (74%, down from 88.9% in 2016). The quantity of oxycodone IR given on discharge complied with quantity guidelines in only 56% of cases. Overall there has been a significant and sustained improvement in appropriateness of discharge analgesia prescribing since 2015, though the results from 2017 show less compliance than 2016 and that achieving compliance with quantity guidelines is an ongoing challenge. This demonstrates the challenge of obtaining high adherence to guidelines over a longer time period.

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Does insomnia modify the association between C-reactive protein and migraine? The Tromsø Study 2015-2016.

The relationship between high sensitivity C-reactive protein and migraine is unclear. The aim of this cross-sectional population-based study was to investigate the association between high sensitivity C-reactive protein and types of headache, and to evaluate the impact of insomnia on this association.

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Could epigenetics help explain racial disparities in chronic pain?

African Americans disproportionately suffer more severe and debilitating morbidity from chronic pain than do non-Hispanic Whites. These differences may arise from differential exposure to psychosocial and environmental factors such as adverse childhood experiences, racial discrimination, low socioeconomic status, and depression, all of which have been associated with chronic stress and chronic pain. Race, as a social construct, makes it such that African Americans are more likely to experience different early life conditions, which may induce epigenetic changes that sustain racial differences in chronic pain. Epigenetics is one mechanism by which environmental factors such as childhood stress, racial discrimination, economic hardship, and depression can affect gene expression without altering the underlying genetic sequence. This article provides a narrative review of the literature on epigenetics as a mechanism by which differential environmental exposure could explain racial differences in chronic pain. Most studies of epigenetic changes in chronic pain examine DNA methylation. DNA methylation is altered in the glucocorticoid (stress response) receptor gene, , which has been associated with depression, childhood stress, low socioeconomic status, and chronic pain. Similarly, DNA methylation patterns of immune cytokine genes have been associated with chronic stress states. Thus, DNA methylation changes may play an essential role in the epigenetic modulation of chronic pain in different races with a higher incidence of epigenetic alterations contributing to more severe and disabling chronic pain in African Americans.

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Psychometric Validation of the Role Function Restrictive Domain of the Migraine Specific Quality-of-Life Questionnaire Version 2.1 Electronic Patient-Reported Outcome in Patients With Episodic and Chronic Migraine.

To assess the measurement properties of the Migraine-Specific Quality of Life Questionnaire version 2.1 (MSQv2.1) electronic patient-reported outcome (ePRO) Role Function-Restrictive (RFR) domain to evaluate the functional impact of migraine in patients with episodic (EM) or chronic migraine (CM) enrolled in clinical trials.

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Patient Preferences for Preventive Migraine Treatments: A Discrete-Choice Experiment.

To understand treatment preferences of people with migraine and the relative importance of improvements in efficacy and avoiding adverse events (AEs), such as cognition problems or weight gain.

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Morphine-dependent and abstinent mice are characterized by a broader distribution of the neurons co-expressing mu and delta opioid receptors.

Opiate addiction develops as a chronic relapsing disorder upon drug recreational use or following misuse of analgesic prescription. Mu opioid (MOP) receptors are the primary molecular target of opiates but increasing evidence support in vivo functional heteromerization with the delta opioid (DOP) receptor, which may be part of the neurobiological processes underlying opiate addiction. Here, we used double knock-in mice co-expressing fluorescent versions of the MOP and DOP receptors to examine the impact of chronic morphine administration on the distribution of neurons co-expressing the two receptors. Our data show that MOP/DOP neuronal co-expression is broader in morphine-dependent mice and is detected in novel brain areas located in circuits related to drug reward, motor activity, visceral control and emotional processing underlying withdrawal. After four weeks of abstinence, MOP/DOP neuronal co-expression is still detectable in a large number of these brain areas except in the motor circuit. Importantly, chronic morphine administration increased the proportion of MOP/DOP neurons in the brainstem of morphine-dependent and abstinent mice. These findings establish persistent changes in the abstinent state that may modulate relapse and opiate-induced hyperalgesia and also point to the therapeutic potential of MOP/DOP targeting.

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Bifunctional opioid receptor ligands as novel analgesics.

Prolonged treatment of chronic severe pain with opioid analgesics is frought with problematic adverse effects including tolerance, dependence, and life-threatening respiratory depression. Though these effects are mediated predominately through preferential activation of μ opioid peptide (μOP) receptors, there is an emerging appreciation that actions at κOP and δOP receptors contribute to the observed pharmacologic and behavioral profile of μOP receptor agonists and may be targeted simultaneously to afford improved analgesic effects. Recent developments have also identified the related nociceptin opioid peptide (NOP) receptor as a key modulator of the effects of μOP receptor signaling. We review here the available literature describing OP neurotransmitter systems and highlight recent drug and probe design strategies.

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Peripheral and central oxidative stress in chemotherapy-induced neuropathic pain.

Chemotherapy-induced peripheral neuropathy (CIPN) is an adverse side effect of many anti-cancer chemotherapeutic treatments. CIPN often causes neuropathic pain in extremities, and oxidative stress has been shown to be a major contributing factor to this pain. In this study, we determined the site of oxidative stress associated with pain (specifically, mechanical hypersensitivity) in cisplatin- and paclitaxel-treated mouse models of CIPN and investigated the neurophysiological mechanisms accounting for the pain. C57BL/6N mice that received either cisplatin or paclitaxel (2 mg/kg, once daily on 4 alternate days) developed mechanical hypersensitivity to von Frey filament stimulations of their hindpaws. Cisplatin-induced mechanical hypersensitivity was inhibited by silencing of Transient Receptor Potential channels V1 (TRPV1)- or TRPA1-expressing afferents, whereas paclitaxel-induced mechanical hypersensitivity was attenuated by silencing of Afibers. While systemic delivery of phenyl N-tert-butylnitrone (PBN), a reactive oxygen species (ROS) scavenger, alleviated mechanical hypersensitivity in both cisplatin- and paclitaxel-treated mice, intraplantar PBN was effective only in cisplatin-treated mice, and intrathecal PBN, only in paclitaxel-treated mice. In a ROS-dependent manner, the mechanosensitivity of A/C fiber endings in the hindpaw skin was increased in cisplatin-treated mice, and the excitatory synaptic strength in the spinal dorsal horn was potentiated in paclitaxel-treated mice. Collectively, these results suggest that cisplatin-induced mechanical hypersensitivity is attributed to peripheral oxidative stress sensitizing mechanical nociceptors, whereas paclitaxel-induced mechanical hypersensitivity is due to central (spinal) oxidative stress maintaining central sensitization that abnormally produces pain in response to Afiber inputs.

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Evaluation of the Preliminary Validity of Misuse of Prescription Pain Medication Items from the Patient-Reported Outcomes Measurement Information System (PROMIS)®.

The National Institutes of Health's Patient-Reported Outcomes Measurement Information System (PROMIS)® includes an item bank for measuring misuse of prescription pain medication (PROMIS-Rx Misuse). The bank was developed and its validity evaluated in samples of community-dwelling adults and patients in addiction treatment programs. The goal of the current study was to investigate the validity of the item bank among patients with mixed-etiology chronic pain conditions.

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A Positive Mood Induction for Reducing the Formation of Nocebo Effects from Side Effect Information.

Providing treatment side effect information can increase the occurrence of side effects through nocebo effects. Nocebo effects from side effect information raise a dilemma for health care, as there is an ethical obligation to disclose potential unpleasant treatment information to patients.

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Low Back Pain, a Comprehensive Review: Pathophysiology, Diagnosis, and Treatment.

Low back pain encompasses three distinct sources: axial lumbosacral, radicular, and referred pain. Annually, the prevalence of low back pain in the general US adult population is 10-30%, and the lifetime prevalence of US adults is as high as 65-80%.

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Lifetime socioeconomic circumstances and chronic pain in later adulthood: findings from a British birth cohort study.

To investigate associations between a range of different indicators of socioeconomic position (SEP: occupational class, education, household overcrowding and tenure, and experience of financial hardship) across life and chronic widespread and regional pain (CWP and CRP) at age 68.

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Ageing alters signalling properties in the mouse spinal dorsal horn.

A well-recognized relationship exists between ageing and increased susceptibility to chronic pain conditions, underpinning the view that pain signaling pathways differ in aged individuals. Yet despite the higher prevalence of altered pain states among the elderly, the majority of preclinical work studying mechanisms of aberrant sensory processing are conducted in juvenile or young adult animals. This mismatch is especially true for electrophysiological studies where patch clamp recordings from aged tissue are generally viewed as particularly challenging. In this study we have undertaken an electrophysiological characterization of spinal dorsal horn neurons in young adult (3-4 months) and aged (28-32 months) mice. We show that patch clamp data can be routinely acquired in spinal cord slices prepared from aged animals and that the excitability properties of aged dorsal horn neurons differ from recordings in tissue prepared from young animals. Specifically, aged dorsal horn neurons more readily exhibit repetitive action potential discharge, indicative of a more excitable phenotype. This observation was accompanied by a decrease in the amplitude and charge of spontaneous excitatory synaptic input to dorsal horn neurons and an increase in the contribution of GABAergic signalling to spontaneous inhibitory synaptic input in aged recordings. While the functional significance of these altered circuit properties remains to be determined, future work should seek to assess if such features may render the aged dorsal horn more susceptible to aberrant injury or disease induced signaling and contribute to increased pain in the elderly.

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Pain is common in chronic fatigue syndrome – current knowledge and future perspectives.

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Spinal glial cell line-derived neurotrophic factor infusion reverses reduction of Kv4.1-mediated A-type potassium currents of injured myelinated primary afferent neurons in a neuropathic pain model.

High frequency spontaneous activity in injured primary afferents has been proposed as a pathological mechanism of neuropathic pain following nerve injury. Although spinal infusion of glial cell line-derived neurotrophic factor (GDNF) reduces the activity of injured myelinated A-fiber neurons after 5th lumbar (L5) spinal nerve ligation (SNL) in rats, the implicated molecular mechanism remains undetermined. The fast-inactivating transient A-type potassium current (IA) is an important determinant of neuronal excitability, and five voltage-gated potassium channel (Kv) alpha-subunits, Kv1.4, Kv3.4, Kv4.1, Kv4.2, and Kv4.3, display IA in heterologous expression systems. Here, we examined the effect of spinal GDNF infusion on IA and the expression of these five Kv mRNAs in injured A-fiber neurons using the in vitro patch clamp technique and in situ hybridization histochemistry. GDNF infusion reversed axotomy-induced reduction of the rheobase, elongation of first spike duration, and depolarization of the resting membrane potential. L5 SNL significantly reduced the current density of IA and GDNF treatment reversed the reduction. Among the examined Kv mRNAs, only the change in Kv4.1-expression was parallel with the change in IA after SNL and GDNF treatment. These findings suggest that GDNF should reduce the hyperexcitability of injured A-fiber primary afferents by IA recurrence. Among the five IA-related Kv channels, Kv4.1 should be a key channel, which account for this IA recurrence.

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CGRP and migraine from a cardiovascular point of view: what do we expect from blocking CGRP?

Calcitonin gene-related peptide (CGRP) is a neuropeptide with a pivotal role in the pathophysiology of migraine. Blockade of CGRP is a new therapeutic target for patients with migraine. CGRP and its receptors are distributed not only in the central and peripheral nervous system but also in the cardiovascular system, both in blood vessels and in the heart. We reviewed the current evidence on the role of CGRP in the cardiovascular system in order to understand the possible short- and long-term effect of CGRP blockade with monoclonal antibodies in migraineurs.In physiological conditions, CGRP has important vasodilating effects and is thought to protect organs from ischemia. Despite the aforementioned cardiovascular implication, preventive treatment with CGRP antibodies has shown no relevant cardiovascular side effects. Results from long-term trials and from real life are now needed.

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ACT for migraine: effect of acceptance and commitment therapy (ACT) for high-frequency episodic migraine without aura: preliminary data of a phase-II, multicentric, randomized, open-label study.

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Longitudinal FDG-PET scan study of brain changes in mice with cancer-induced bone pain and after morphine analgesia.

Morphine is the most commonly used drug for treating physical and psychological suffering caused by advanced cancer. Although morphine is known to elicit multiple supraspinal analgesic effects, its behavioral correlates with respect to the whole brain metabolic activity during cancer-induced bone pain have not been elucidated. We injected 4T1 mouse breast cancer cells into the left femur bone marrow cavity of BALB/c mice. All mice developed limb use deficits, mechanical allodynia, and hypersensitivity to cold, which were effectively suppressed with morphine. Serial 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) was performed for each mouse before cancer induction (0 d), after cancer-induced bone pain was established (14 d), and during effective morphine treatment (16 d). The longitudinal FDG-PET imaging analysis demonstrated that cancer-induced bone pain increased glucose uptake in the insular cortex and hypothalamus and decreased the activity of the retrosplenial cortex. Morphine reversed the activation of the insular cortex and hypothalamus. Furthermore, morphine activated the amygdala and rostral ventromedial medulla and suppressed the activity of anterior cingulate cortex. Our findings of hypothalamic and insular cortical activation support the hypothesis that cancer-induced bone pain has strong inflammatory and affective components in freely moving animals. Morphine may provide descending inhibitory and facilitatory actions in the treatment of cancer-induced bone pain in a clinical setting.

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Blocking αδ-1 Subunit Reduces Bladder Hypersensitivity and Inflammation in a Cystitis Mouse Model by Decreasing NF-kB Pathway Activation.

Bladder pain is frequently associated with bladder inflammation, as in conditions like interstitial cystitis (IC), for which current analgesic therapies have limited efficacy. The antinociceptive effect of alpha-2-delta (αδ) ligands on inflammation-associated visceral pain like that experienced in cystitis has been poorly investigated. To investigate the effect of pregabalin (PGB), an αδ ligand, we evaluated its impact on mechanical hyperalgesia in a mouse model of cystitis induced by cyclophosphamide (CYP). We further studied its effect on inflammation and NF-kB pathway activation. Acute cystitis was induced by intraperitoneal injection of 150 mg kg of CYP in C57Bl/6J male mice. PGB was subcutaneously injected (30 mg kg) 3 h after CYP injection. The effect of PGB on CYP-induced mechanical referred hyperalgesia (abdominal Von Frey test), inflammation (organ weight, cytokine production, αδ subunit level, NF-kB pathway activation) were assessed 1 h after its injection. In parallel, its effect on cytokine production, αδ subunit level and NF-kB pathway activation was assessed on peritoneal exudate cells (PECs) stimulated with LPS. PGB treatment decreased mechanical referred hyperalgesia. Interestingly, it had an anti-inflammatory effect in the cystitis model by reducing pro-inflammatory cytokine production. PGB also inhibited NF-kB pathway activation in the cystitis model and in macrophages stimulated with LPS, in which it blocked the increase in intracellular calcium. This study shows the efficacy of PGB in hypersensitivity and inflammation associated with cystitis. It is therefore of great interest in assessing the benefit of αδ ligands in patients suffering from cystitis.

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Antidepressant Use Among People Prescribed Opioids for Chronic Noncancer Pain.

Although depression and chronic pain often coexist, few studies have examined antidepressant use among people with pain. This study examines the prevalence and characteristics associated with antidepressant use among people prescribed opioids for chronic noncancer pain (CNCP).

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EAN guideline on trigeminal neuralgia.

Trigeminal neuralgia (TN) is an extremely painful condition, which can be difficult to diagnose and treat. In Europe, TN-patients are managed by many different specialities. Therefore, there is a great need for comprehensive European guidelines for management of TN. The European Academy of Neurology asked an expert panel to develop recommendations for a series of questions that are essential for daily clinical management of patients with TN.

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Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats.

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

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Foxp3 plasmid-encapsulated PLGA nanoparticles attenuate pain behavior in rats with spinal nerve ligation.

Microglia play a critical role in neuropathic pain. Since upregulated Foxp3 in microglia enhances tissue repair by resolving neuroinflammation in excitotoxin-induced neuronal death, it may attenuate neuropathic pain in a similar manner. Therefore, this study tests whether Foxp3 introduced with poly (D, L-lactic-co-glycolic acid) (PLGA) nanoparticles (Foxp3 NPs) can alleviate neuropathic pain by inhibiting microglia activity. The prepared Foxp3 NPs had an anti-inflammatory effect on lipopolysaccharide-stimulated BV2 cells in vitro, and localized to spinal microglia in vivo. Further, the Foxp3 NPs significantly attenuated pain behavior induced by spinal nerve ligation in rats for 7days by suppressing microglial activity, followed by the downregulation of pro-nociceptive genes and the upregulation of anti-nociceptive genes in the spinal dorsal horn. Collectively, these data suggest that Foxp3 NPs effectively relieve neuropathic pain in animals by reducing microglia activity and subsequent modulation of neuroinflammation, and may be of therapeutic value in the treatment of neuropathic pain.

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Field testing the diagnostic criteria of cluster headache in the third edition of the International Classification of Headache Disorders: A cross-sectional multicentre study.

*These authors are shared first authors. The recently published third edition of the International Classification of Headache Disorders (ICHD-3) revised the criteria for accompanying symptoms of cluster headache (CH) and the remission period of chronic cluster headache (CCH). This study aimed at testing the validity of the ICHD-3 criteria for CH by using data from the Korean Cluster Headache Registry.

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Sex Differences in a Rodent Model of HIV-1-Associated Neuropathic Pain.

Worldwide, women account for approximately 51% of human immunodeficiency virus-1 (HIV) seropositive individuals. The prevalence of neuropathic pain among individuals with HIV and a lack of preclinical data characterizing sex differences prompted us to address this knowledge gap. C57BL/6 male and female mice received multiple intrathecal injections of HIV-glycoprotein 120 (gp120), followed by determination of mechanical allodynia and thermal hypersensitivity for four weeks. The influence of ovarian hormones in the gp120 pain model was evaluated by comparison of ovariectomized (OVX) mice versus sham control. We found that gp120-induced neuropathic pain-like behaviors are sex-dependent. Female mice showed both increased mechanical allodynia and increased cold sensitivity relative to their male counterparts. The OVX mice showed reduced pain sensitivity compared to sham, suggesting a role of the ovarian hormones in sex differences in pain sensitivity to gp120. Gp120-induced neuropathic pain caused a shift in estrous cycle toward the estrus phase. However, there is a lack of clear correlation between the estrous cycle and the development of neuropathic pain-like behaviors during the four week recording period. This data provided the first evidence for sex differences in a rodent model of HIV-related neuropathic pain, along with a potential role of ovarian hormones.

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Assessment of conditioned pain modulation in healthy participants and patients with chronic pain: manifestations and implications for pain progression.

The purpose of this review is to summarize recent findings on conditioned pain modulation (CPM) in humans with a focus on methodology, factors modulating CPM, and the potential for CPM as a clinical marker for pain progression.

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Modulation by Sigma-1 Receptor of Morphine Analgesia and Tolerance: Nociceptive Pain, Tactile Allodynia and Grip Strength Deficits During Joint Inflammation.

Sigma-1 receptor antagonism increases the effects of morphine on nociceptive pain, even in morphine-tolerant animals. However, it is unknown whether these receptors are able to modulate morphine antinociception and tolerance during inflammatory pain. Here we used a mouse model to test the modulation of morphine effects by the selective sigma-1 antagonist S1RA (MR309), by determining its effect on inflammatory tactile allodynia (von Frey filaments) and on grip strength deficits induced by joint inflammation (a measure of pain-induced functional disability), and compared the results with those for nociceptive heat pain recorded with the unilateral hot plate (55°C) test. The subcutaneous (s.c.) administration of morphine induced antinociceptive effects to heat stimuli, and restored mechanical threshold and grip strength in mice with periarticular inflammation induced by Complete Freund's Adjuvant. S1RA (80 mg/kg, s.c.) administered alone did not induce any effect on nociceptive heat pain or inflammatory allodynia, but was able to partially reverse grip strength deficits. The association of S1RA with morphine, at doses inducing little or no analgesic-like effects when administered alone, resulted in a marked antinociceptive effect to heat stimuli and complete reversion of inflammatory tactile allodynia. However, S1RA administration did not increase the effect of morphine on grip strength deficits induced by joint inflammation. When S1RA (80 mg/kg, s.c.) was administered to morphine-tolerant animals, it rescued the analgesic-like effects of this opioid in all three pain measures. However, when S1RA was repeatedly given during the induction of morphine tolerance (and not on the day of behavioral evaluation) it failed to affect tolerance to the effects of morphine on nociceptive heat pain or inflammatory allodynia, but completely preserved the effects of this opioid on grip strength deficits. These effects of S1RA on morphine tolerance cannot be explained by pharmacokinetic interactions, given that the administration of S1RA did not modify concentrations of morphine or morphine-3-glucuronide (a major morphine metabolite) in morphine-tolerant animals in plasma or brain tissue. We conclude that sigma-1 receptors play a pivotal role in the control of morphine analgesia and tolerance in nociceptive and inflammatory pain, although in a manner dependent on the type of painful stimulus explored.

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Chronic Pain and Chronic Opioid Use After Intensive Care Discharge – Is It Time to Change Practice?

Almost half of patients treated on intensive care unit (ICU) experience moderate to severe pain. Managing pain in the critically ill patient is challenging, as their pain is complex with multiple causes. Pharmacological treatment often focuses on opioids, and over a prolonged admission this can represent high cumulative doses which risk opioid dependence at discharge. Despite analgesia the incidence of chronic pain after treatment on ICU is high ranging from 33-73%. Measures need to be taken to prevent the transition from acute to chronic pain, whilst avoiding opioid overuse. This narrative review discusses preventive measures for the development of chronic pain in ICU patients. It considers a number of strategies that can be employed including non-opioid analgesics, regional analgesia, and non-pharmacological methods. We reason that individualized pain management plans should become the cornerstone for critically ill patients to facilitate physical and psychological well being after discharge from critical care and hospital.

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Resting State Functional Connectivity of the Rat Claustrum.

The claustrum is structurally connected with many cortical areas.A major hurdle standing in the way of understanding claustrum function is the difficulty in assessing the global functional connectivity (FC) of this structure. The primary issues lie in the inability to isolate claustrum signal from the adjacent insular cortex (Ins), caudate/putamen (CPu), and endopiriform nucleus (Endo). To address this issue, we used (7T) fMRI in the rat and describe a novel analytic method to study claustrum without signal contamination from the surrounding structures. Using this approach, we acquired claustrum signal distinct from Ins, CPu, and Endo, and used this claustrum signal to determine whole brain resting state functional connectivity (RSFC). Claustrum RSFC was distinct from the adjacent structures and displayed extensive connections with sensory cortices and the cingulate cortex, consistent with known structural connectivity of the claustrum. These results suggest fMRI and improved analysis can be combined to accurately assay claustrum function.

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‘How does change unfold?’ an evaluation of the process of change in four people with chronic low back pain and high pain-related fear managed with Cognitive Functional Therapy: A replicated single-case experimental design study.

To understand the process of change at an individual level, this study used a single-case experimental design to evaluate how change in potential mediators related to change in disability over time, during an exposure-based behavioural intervention in four people with chronic low back pain and high pain-related fear. A second aim was to evaluate whether the change (sequential or simultaneous) in mediators and disability occurred at the same timepoint for all individuals.

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Differential effect of LPS and paclitaxel on microglial functional phenotypes and circulating cytokines: the possible role of CX3CR1 and IL-4/10 in blocking persistent inflammation.

Neuroinflammation plays a role in cancer chemotherapy-induced chronic pain. Thus far, most studies have focused on neuroinflammation suppression. However, there are limited reports of which factor is involved in the transition from acute inflammation to chronic inflammation, resulting in neuroinflammation and chronic pain. Here, we compared the inflammatory reaction and pain response induced by LPS and paclitaxel. LPS (0.5 mg/kg) or paclitaxel (2 mg/kg/day for 5 days) was administered intraperitoneally to mice, and mechanical allodynia was examined by von Frey test. LPS induced transient mechanical allodynia, whereas paclitaxel induced persistent mechanical allodynia. The CD86/CX3CR1 ratio remained unchanged due to CX3CR1 elevation following LPS injection, whereas the ratio was increased on day 1 after paclitaxel injection. LPS also increased CD45, CCL2, and CCL5 mRNA in the spinal cord and circulating pro- and anti-inflammatory cytokines 1 day after injection; however, the pattern was not consistent. Paclitaxel gradually increased inflammatory cytokines in the spinal cord. CX3CR1 might be involved in blocking the transition from acute pain to persistent pain in the LPS group. In addition, serum IL-4 and IL-10 elevation in the LPS group may be associated with chronic pain prevention. Therefore, targeting CX3CR1, IL-4, and IL-10 might be an alternative therapeutic strategy.

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Ingrowth of Nociceptive Receptors into Diseased Cervical Intervertebral Disc Is Associated with Discogenic Neck Pain.

To investigate the distribution of nociceptive nerve fibers in the cervical intervertebral discs of patients with chronic neck pain and determine whether these nociceptive nerve fibers are related to discogenic neck pain.

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A Systematic Review and Meta-analysis of Memantine for the Prevention or Treatment of Chronic Pain.

N-methyl-D-aspartate (NMDA) receptors are involved in pain signalling and neuroplasticity. Memantine has been shown to have analgesic properties in pre-clinical and small clinical studies. We conducted a systematic review and meta-analysis to assess the efficacy of memantine to prevent or reduce chronic pain.

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Assessment of experimental orofacial pain, pleasantness and unpleasantness via standardised psychophysical testing.

Somatosensory assessment within the orofacial region may be performed using highly standardised quantitative sensory testing (QST). However, the function of the C tactile (CT) afferent, a nerve fibre linked to the perception of pleasant touch, is usually not evaluated. Furthermore, the perception of unpleasantness is also rarely assessed; a dimension not only limited to a painful experience. Therefore, the primary aim was to apply standardised QST stimuli as well as standardised pleasant stimuli and evaluate their potential capacity for evocation of perceived pain, pleasant and unpleasant sensations in the facial region.

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Opioid use after hip fracture surgery: A Danish nationwide cohort study from 2005-2015.

There is currently a knowledge gap regarding persistent opioid use after hip fracture surgery. Thus, opioid use within a year after hip fracture surgery in patients with/without opioid use before surgery was examined.

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Treatment of Vulvodynia: Pharmacological and Non-Pharmacological Approaches.

Vulvodynia is a common, recurrent, vulvar pain condition with debilitating consequences for affected women's health and quality of life. The heterogeneity of women suffering from vulvodynia as well as its uncertain and likely multifactorial etiology pose a significant challenge to identifying any kind of "gold standard" treatment. Thus, treatment providers must be well versed in the various options and the evidence for each. In this review, we begin with pharmacological treatments, followed by non-pharmacological treatments, surgery, and finally multimodal treatments. For each approach, we briefly discuss the method, mechanism of action, and empirical support for the treatment. In sum, pharmacological treatments that may be beneficial but require further research include antinociceptive agents (lidocaine, capsaicin), anti-inflammatory agents (corticosteroids, interferon), neuromodulating medications (anticonvulsants and antidepressants), hormonal agents, and muscle relaxants (e.g., botulinum toxin). There is strong evidence to support and recommend non-pharmacological interventions including psychological therapy, pelvic floor physical therapy, as well as surgery (i.e., vestibulectomy for provoked vestibulodynia) for the treatment of vulvodynia. We conclude this review with a discussion of issues that may have hindered progress of treatment efficacy and effectiveness, and recommendations for moving the field forward.

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An open-label prospective study of the real-life use of onabotulinumtoxinA for the treatment of chronic migraine: the REPOSE study.

The PREEMPT Studies established onabotulinumtoxinA as preventive treatment for adults with chronic migraine (CM). The purpose of the REal-life use of botulinum toxin for the symptomatic treatment of adults with chronic migraine, measuring healthcare resource utilisation, and Patient-reported OutcomeS observed in practice (REPOSE) Study was to observe real-life, long-term (24-month) use of onabotulinumtoxinA in adults with CM and report on the utilisation, effectiveness, safety, and tolerability.

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Promote Biomarker Discovery by Identifying Homogenous Primary Headache Subgroups.

Within- and between-study heterogeneity impede identification of valid primary headache biomarkers. Homogenous subgroup identification and investigation of differential biochemical profiles and networks within and across headache categories, based on statistical techniques, might promote biomarker discovery. When studying common primary headaches with a multifactorial etiology, variability might be captured at different levels (eg, genetics, clinical features, comorbidities, triggers). Moreover, focus on biochemical profiles instead of single compounds is crucial to develop strategies for accurate differential diagnosis.

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Spinal Cord Stimulation: Comparing Traditional Low-frequency Tonic Waveforms to Novel High Frequency and Burst Stimulation for the Treatment of Chronic Low Back Pain.

The purpose of the present investigation is to summarize supporting evidence for novel sub-perception spinal cord stimulation (SCS) therapy over traditional paresthesia inducing low-frequency waveforms for the treatment of chronic pain. The focus of this review is to summarize key studies comparing traditional low-frequency tonic waveforms to modern high frequency and burst stimulation for the treatment of patients with chronic intractable low back pain and/or leg pain.

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Catastrophizing attitude changes after onabotulinumtoxin A treatment in chronic migraine.

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An Open-Label, 52-Week, Phase III Trial of Duloxetine in Japanese Patients with Chronic Low Back Pain.

To evaluate the safety and efficacy of duloxetine treatment for 52 weeks.

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Cerebral venous outflow in migraine.

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The use of opioids for chronic non-cancer pain in older Australians.

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Physical Therapy Outcome Measures for Assessment of Lower Extremity Chronic Pain-Related Function in Pediatrics.

To assess the clinical utility of 5 physical therapy (PT) outcome measures in quantifying functional changes in pediatric lower extremity chronic pain treated at a hospital-based interdisciplinary rehabilitation center.

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Gender differences in associations between pain-related anxiety and alcohol use among adults with chronic pain.

Over 100 million Americans live with chronic pain, and adults with chronic pain may be more likely to experience alcohol-related problems or Alcohol Use Disorder. An evolving conceptual model posits that bidirectional effects between pain and alcohol exacerbate both pain and drinking. Pain has been shown to motivate alcohol urge and consumption, and drinking for pain-coping predicts escalations in alcohol use over time. Pain-related anxiety is a transdiagnostic vulnerability factor that has been implicated in both pain and substance-related (i.e., tobacco, opioids, cannabis) outcomes, but has not yet been studied in relation to alcohol use.

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TRPV1 channel contributes to remifentanil-induced postoperative hyperalgesia via regulation of NMDA receptor trafficking in dorsal root ganglion.

Remifentanil is widely used in general anesthesia due to its reliability and rapid onset. However, remifentanil-induced postoperative hyperalgesia might be a challenge nowadays. Accumulating evidence suggests that the transient receptor potential vanilloid 1 (TRPV1) was involved in the development of neuropathic pain and hyperalgesia. However, the contribution of TRPV1 in modulating remifentanil-induced postoperative hyperalgesia is still unknown. The aim of this study is the contribution of TRPV1 to the surface expression of -methyl-d-aspartate (NMDA) receptors in remifentanil-induced postoperative hyperalgesia.

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Gabapentin versus Transdermal Fentanyl Matrix for the Alleviation of Chronic Neuropathic Pain of Radicular Origin: A Randomized Blind Multicentered Parallel-Group Noninferiority Trial.

A number of studies have been published proposing various approaches to the treatment of neuropathic pain; however, to our knowledge, no attempts have been made to compare gabapentin and fentanyl in patients with lumbar radiculopathy. We evaluated the relative efficacy and safety of fentanyl matrix and gabapentin for the treatment of chronic neuropathic pain of radicular origin. The study was designed as a randomized blind multicentered parallel-group noninferiority trial. A total of 108 patients with moderate-to-severe pain (≥4 intensity on an 11-point numeric rating scale) were randomly prescribed either fentanyl matrix or gabapentin over a period of 56 days. In the primary analysis, the noninferiority of fentanyl matrix treatment was evaluated in relation to the efficacy of gabapentin based on the pain intensity difference (PID) at 56 days after the first dose of the drugs. Secondary endpoints included pain relief, improvement in functional status (the Korean-Oswestry Disability Index (K-ODI)), improvement in depressive symptoms (Korean-Beck Depression Index (K-BDI)) between the 28th and 56th day, and adverse events (AEs). Analysis of the primary efficacy endpoint established the noninferiority of fentanyl matrix compared with gabapentin, with no statistically significant difference observed in the PID after 56 days for the two treatment groups. Similarly, analysis of pain relief revealed no significant differences between the groups on days 28 and 56. There was no difference in the K-ODI and K-BDI between the groups during the study period. The overall incidence of at least one AE was similar for fentanyl matrix (67.3%) and gabapentin (69.6%). The most commonly reported AEs for patients treated with fentanyl matrix and gabapentin included dizziness (30.8% vs. 44.6%, respectively), somnolence (26.9% vs. 35.7%), and constipation (15.4% vs. 17.9%). This study demonstrated that the analgesic effect of fentanyl matrix is noninferior in comparison with gabapentin and supports the use of fentanyl matrix as an effective and safe treatment for moderate-to-severe chronic neuropathic pain. This trial is registered with NCT01127100.

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Paresthesia-Free Dorsal Root Ganglion Stimulation: An ACCURATE Study Sub-Analysis.

ACCURATE, a randomized controlled trial comparing dorsal root ganglion (DRG) stimulation to spinal cord stimulation, showed that DRG stimulation is a safe and effective therapy in individuals with lower extremity chronic pain due to complex regional pain syndrome (CRPS) type I or II. Investigators noted that DRG stimulation programming could be adjusted to minimize, or eliminate, the feeling of paresthesia while maintaining adequate pain relief. The present study explores treatment outcomes for DRG subjects who were paresthesia-free vs. those who experienced the sensation of paresthesia, as well as the factors that predicted paresthesia-free analgesia.

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Analysis of Multiple Routes of Analgesic Administration in the Immediate Postoperative Period: a 10-Year Experience.

An increasing amount of literature supports a multimodal approach to analgesic administration in the management of postoperative pain. The purpose of this study and review was to further evaluate the differences in efficacy in controlling immediate postoperative pain among the various routes of analgesia administration.

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Characterization of Cancer-Induced Nociception in a Murine Model of Breast Carcinoma.

Severe and poorly treated pain often accompanies breast cancer. Thus, novel mechanisms involved in breast cancer-induced pain should be investigated. Then, it is necessary to characterize animal models that are reliable with the symptoms and progression of the disease as observed in humans. Explaining cancer-induced nociception in a murine model of breast carcinoma was the aim of this study. 4T1 (10) lineage cells were inoculated in the right fourth mammary fat pad of female BALB/c mice; after this, mechanical and cold allodynia, or mouse grimace scale (MGS) were observed for 30 days. To determine the presence of bone metastasis, we performed the metastatic clonogenic test and measure calcium serum levels. At 20 days after tumor induction, the antinociceptive effect of analgesics used to relieve pain in cancer patients (acetaminophen, naproxen, codeine or morphine) or a cannabinoid agonist (WIN 55,212-2) was tested. Mice inoculated with 4T1 cells developed mechanical and cold allodynia and increased MGS. Bone metastasis was confirmed using the clonogenic assay, and hypercalcemia was observed 20 days after cells inoculation. All analgesic drugs reduced the mechanical and cold allodynia, while the MGS was decreased only by the administration of naproxen, codeine, or morphine. Also, WIN 55,212-2 improved all nociceptive measures. This pain model could be a reliable form to observe the mechanisms of breast cancer-induced pain or to observe the efficacy of novel analgesic compounds.

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Memantine selectively prevented the induction of dynamic allodynia by blocking Kir2.1 channel and inhibiting the activation of microglia in spinal dorsal horn of mice in SNI model.

Memantine (MEM) is one of the important clinical medications in treating moderate to severe Alzheimer disease. The effect of MEM on preventing or treating punctate allodynia has been thoroughly studied but not on the induction of dynamic allodynia. The aim of this study is to investigate whether MEM could prevent the induction of dynamic allodynia and its underlying spinal mechanisms. 1)in vivo SNI pain model, pretreatment with MEM at a lower dose (10nmol, i.t.; MEM-10) selectively prevented the induction of dynamic allodynia, but not the punctate allodynia. 2) Pretreatment with either MK801-10 (MK801-10nmol, i.t.) or higher dose of MEM (30nmol, i.t.; MEM-30) prevented the induction of both dynamic and punctate allodynia. 3) MEM-10 showed significant effect on the inhibition of the SNI induced overactivation of microglia in spinal dorsal horn. 4) In contrast, in CFA model, MEM-10 neither affected the CFA injection induced activation of microglia in spinal dorsal horn nor the induction of dynamic allodynia. 5) Immunohistology studies showed Kir2.1 channel distributed widely and co-localized with microglia in the spinal dorsal horn of mice. 6) Pretreatment with either minocycline, a microglia inhibitor, or ML133, a Kir2.1 inhibitor, both selectively prevented the overactivation of microglia in spinal dorsal horn, and the induction of dynamic allodynia following SNI. The selectively inhibitory effect on the induction of dynamic allodynia in SNI model by low dose of the memantine (MEM-10) was tightly correlated with the blockade of microglia Kir2.1 channel to suppress the microglia activation.

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Almotriptan: a review of 20 years’ clinical experience.

Almotriptan, a serotonin 5-HT agonist has been used in the acute treatment of migraine with or without aura for 20 years, accumulating data on more than 15,000 patients in studies and from an estimated >150 million treated migraine attacks in daily clinical practice. The last major review of almotriptan was written almost 10 years ago. The current narrative review provides an overview of the experience gained with almotriptan over that time, and highlights data published in the last decade. Areas covered: Randomized clinical trials, observational studies, postmarketing studies and meta-analyses involving almotriptan for the treatment of acute migraine identified through a systematic literature search. Expert opinion: Triptans are a mainstay of anti-migraine treatment. Findings with ALT over the last 10 years have reinforced the positive efficacy and tolerability results that were reported during the first 10 years following its introduction. In particular, more recent clinical results have confirmed its efficacy in women with menstrual migraine, the usefulness of early intervention, long-term benefit in adults, and also its efficacy and safety in adolescents. Overall, ALT can be considered an optimal choice for managing acute migraine resistant to first-line drugs.

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