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Papers: 25 Jan 2020 - 31 Jan 2020

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The influence of visual experience and cognitive goals on the spatial representations of nociceptive stimuli.

Localizing pain is crucial because it allows for detecting which part of the body is being hurt and identifying in its surrounding which stimulus is producing the damage. Nociceptive inputs should therefore be mapped according to somatotopic ("which limb is stimulated?") and spatiotopic representations ("where is the stimulated limb?"). Because the body posture constantly changes, the brain has to realign the different spatial representations, for instance when the arms are crossed with the left hand in the right space and vice versa, to adequately guide actions towards the threatening object. Such ability is thought to be dependent on past sensory experience and contextual factors. We compared performances of early blind and normally sighted participants during temporal order judgement tasks. Two nociceptive stimuli were applied, one on each hand, with the hands either uncrossed or crossed. Participants reported which stimulus they perceived as first presented, according to either its location on the body or the position of the stimulated hand, respectively, prioritizing anatomy or external space as task-relevant reference frame. Relative to the uncrossed posture, sighted participants' performances were decreased when the hands were crossed, whatever the instruction be. Early blind participants' performances were affected by crossing the hands during spatial instruction, but not during anatomical instruction. These results indicate that nociceptive stimuli are automatically coded according to both somatotopic and spatiotopic representations, but the integration of the different spatial reference frames depends on early visual experience and ongoing cognitive goals, illustrating the plasticity and the flexibility of the nociceptive system.

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Epithelial-Neuronal Communication in the Colon: Implications for Visceral Pain.

Visceral hypersensitivity and pain result, at least in part, from increased excitability of primary afferents that innervate the colon. In addition to intrinsic changes in these neurons, emerging evidence indicates that changes in lining epithelial cells may also contribute to increased excitability. Here we review recent studies on how colon epithelial cells communicate directly with colon afferents. Specifically, anatomical studies revealed specialized synaptic connections between epithelial cells and nerve fibers and studies using optogenetic activation of the epithelium showed initiation of pain-like responses. We review the possible mechanisms of epithelial-neuronal communication and provide an overview of the possible neurotransmitters and receptors involved. Understanding the biology of this interface and how it changes in pathological conditions may provide new treatments for visceral pain conditions.

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Limited engagement with transparent and open science standards in the policies of pain journals: a cross-sectional evaluation.

Scientific progress requires transparency and openness. The ability to critique, replicate and implement scientific findings depends on the transparency of the study design and methods, and the open availability of study materials, data and code. Journals are key stakeholders in supporting transparency and openness. This study aimed to evaluate 10 highest ranked pain journals' authorship policies with respect to their support for transparent and open research practices. Two independent authors evaluated the journal policies (as at 27 May 2019) using three tools: the self-developed Transparency and Openness Evaluation Tool, the Centre for Open Science (COS) Transparency Factor and the International Committee of Medical Journal Editors (ICMJE) requirements for disclosure of conflicts of interest. We found that the journal policies had an overall low level of engagement with research transparency and openness standards. The median COS Transparency Factor score was 3.5 (IQR 2.8) of 29 possible points, and only 7 of 10 journals' stated requirements for disclosure of conflicts of interest aligned fully with the ICMJE recommendations. Improved transparency and openness of pain research has the potential to benefit all that are involved in generating and using research findings. Journal policies that endorse and facilitate transparent and open research practices will ultimately improve the evidence base that informs the care provided for people with pain.

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GPR160 de-orphanization reveals critical roles in neuropathic pain in rodents.

Treating neuropathic pain is challenging and novel non-opioid based medicines are needed. Using unbiased receptomics, transcriptomic analyses, immunofluorescence and in situ hybridization, we found the expression of the orphan GPCR (oGPCR) Gpr160 and GPR160 increased in the rodent dorsal horn of the spinal cord (DH-SC) following traumatic nerve injury. Genetic and immunopharmacological approaches demonstrated that GPR160 inhibition in the spinal cord prevented and reversed neuropathic pain in male and female rodents without altering normal pain response. GPR160 inhibition in the spinal cord attenuated sensory processing in the thalamus, a key relay in the sensory discriminative pathways of pain. We also identified cocaine- and amphetamine-regulated transcript peptide (CARTp) as a GPR160 ligand. Inhibiting endogenous CARTp signaling in spinal cord attenuated neuropathic pain, whereas exogenous intrathecal (i.th.) CARTp evoked painful hypersensitivity through GPR160-dependent ERK and cAMP response element-binding protein (CREB). Our findings de-orphanize GPR160, identify it as a determinant of neuropathic pain and potential therapeutic target, and provide insights to its signaling pathways. CARTp is involved in many diseases including depression, reward and addiction, de-orphanization of GPR160 is a major step forward understanding the role of CARTp signaling in health and disease.

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Chronic non-inflammatory muscle pain: central and peripheral mediators.

Conditions with chronic widespread non-inflammatory muscle pain, such as fibromyalgia, have complex etiologies with numerous proposed mechanisms for their pathophysiology of underlying chronic pain. Advancements in neuroimaging have allowed for the study of brain function and connectivity in humans with these conditions, while development of animal models have allowed for the study of both peripheral and central factors that lead to chronic pain. This article reviews the current literature surrounding the pathophysiology of chronic widespread non-inflammatory muscle pain focusing on both peripheral and central nervous system, as well as immune system, contributions to the development and maintenance of pain. A better understanding of the mechanisms underlying these conditions can allow for improvements in patient education, treatment and outcomes.

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Magnetic resonance imaging of neuroinflammation in chronic pain: a role for astrogliosis?

Non-invasive measures of neuroinflammatory processes in humans could substantially aid diagnosis and therapeutic development for many disorders, including chronic pain. Several proton Magnetic Resonance Spectroscopy (H-MRS) metabolites have been linked with glial activity (i.e. choline and myo-inositol) and found to be altered in chronic pain patients, but their role in the neuroinflammatory cascade is not well known. Our multimodal study evaluated resting fMRI connectivity and H-MRS metabolite concentration in insula cortex in 43 patients suffering from fibromyalgia, a chronic centralized pain disorder previously demonstrated to include a neuroinflammatory component, and 16 healthy controls. Patients demonstrated elevated choline (but not myo-inositol) in anterior insula (p=0.03), with greater choline levels linked with worse pain interference (r=0.41, p=0.01). In addition, reduced resting functional connectivity between anterior insula and putamen was associated with both pain interference (whole brain analysis, pcorrected<0.01) and elevated anterior insula choline (r=-0.37, p=0.03). In fact, anterior insula/putamen connectivity statistically mediated the link between anterior insula choline and pain interference (p<0.01), highlighting the pathway by which neuroinflammation can impact clinical pain dysfunction. In order to further elucidate the molecular substrates of the effects observed, we investigated how putative neuroinflammatory H-MRS metabolites are linked with ex-vivo tissue inflammatory markers in a nonhuman primate model of neuroinflammation. Results demonstrated that cortical choline levels were correlated with glial fibrillary acidic protein, a known marker for astrogliosis (Spearman r=0.49, p=0.03). Choline, a putative neuroinflammatory H-MRS assessed metabolite elevated in fibromyalgia and associated with pain interference, may be linked with astrogliosis in these patients.

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Outcomes of prescription opioid dose escalation for chronic pain: results from a prospective cohort study.

The use of long-term opioid therapy for chronic pain remains common, yet data on long-term outcomes, especially after dose escalation, are sparse. This study examined potential benefits and harms associated with prescription opioid dose escalation. Participants from two institutions were enrolled in a two-year prospective cohort study. All participants (n=517) had a musculoskeletal pain diagnosis and were receiving a stable dose of long-term opioid therapy at baseline. Participants completed self-report measures of pain, disability, depression, and potential adverse effects at baseline and every six months for two years. We reviewed electronic health record data weekly to identify episodes of prescription opioid dose escalation; participants who had increases in their dose were seen for additional research visits within one month of dose escalation. Over two years, 19.5% of participants had prescription opioid dose increases. After controlling for covariates, there were no significant changes on any variable following dose escalation. Of those with a dose increase, 3% experienced a clinically meaningful improvement in pain following dose escalation. Participants in the entire sample had small improvements in pain intensity, depressive symptoms, medication-related side effects, and lower risk for prescription opioid misuse during the study period. Sexual functioning worsened over time. There were no significant changes in the full sample on pain disability, sleep functioning, or experiencing a fall. In summary, patients prescribed stable doses of long-term opioid therapy may demonstrate small changes in key pain-related outcomes over time, but prescription opioid dose escalation status is unrelated to clinical outcomes.

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Functional expression and pharmacological modulation of TRPM3 in human sensory neurons.

The transient receptor potential (TRP) ion channel TRPM3 functions as a noxious heat sensor and plays a key role in acute pain sensation and inflammatory hyperalgesia in rodents. Despite its potential as novel analgesic drug target, little is known about the expression, function and modulation of TRPM3 in the human somatosensory system.

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Is transcranial direct current stimulation (tDCS) effective for the treatment of pain in fibromyalgia? A systematic review and meta-analysis.

Fibromyalgia is a debilitating condition characterized by chronic widespread pain. It is believed to be caused by dysfunction of the central nervous system (CNS) but current treatments are largely ineffective. Transcranial Direct Current Stimulation (tDCS), a neuromodulation technique that targets the CNS, may offer a new line of treatment.

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Microarray Analyses of the Dorsal Root Ganglia Support a Role for Innate Neuro-Immune Pathways in Persistent Pain in Experimental Osteoarthritis.

Following destabilization of the medial meniscus (DMM), mice develop experimental osteoarthritis (OA) and associated pain behaviors that are dependent on the stage of disease. We aimed to describe changes in gene expression in knee-innervating dorsal root ganglia (DRG) after surgery, in order to identify molecular pathways associated with three pre-defined pain phenotypes: "post-surgical pain", "early-stage OA pain", and "persistent OA pain".

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Understanding suicidal ideation and behaviour in individuals with chronic pain: a review of the role of novel transdiagnostic psychological factors.

Individuals with chronic pain are at an elevated risk of suicide, yet psychosocial factors that might be involved in increasing or decreasing vulnerability for suicidal ideation and behaviour have received little attention. Extant literature on the topic of suicide in individuals with chronic pain incorporates only a few of the wide array of known vulnerability and protective factors. This Review focuses on transdiagnostic psychological processes, (ie, those of relevance for both chronic pain and suicide). We reviewed a selection of published literature on chronic pain and suicide, concentrating on previously unexplored and underexplored lines of research, including future orientation, mental imagery, and psychological flexibility. A greater degree of crosspollination between the fields of chronic pain and suicide research is required to progress our understanding of why some people with chronic pain become suicidal and others do not.

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Higher burden of rare frameshift indels in genes related to synaptic transmission separate familial hemiplegic migraine from common types of migraine.

Familial hemiplegic migraine (FHM) is a rare form of migraine with aura that often has an autosomal dominant mode of inheritance. Rare mutations in the , and genes can all cause FHM revealing genetic heterogeneity in the disorder. Furthermore, only a small subset of the affected individuals has a causal mutation. We set out to investigate what differentiates patients with FHM with no mutation in any known FHM gene from patients with common types of migraine in both familial and sporadic cases.

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CRPS is not associated with altered sensorimotor cortex GABA or glutamate.

Complex regional pain syndrome (CRPS) is a debilitating chronic pain disorder typically in the upper or lower limbs. Whilst CRPS usually develops from a peripheral event, it is likely maintained by central nervous system changes. Indeed CRPS is reported to be associated with sensorimotor cortex changes, or functional 'reorganisation', as well as deficits such as poor tactile acuity. Whilst the mechanisms underpinning cortical reorganisation in CRPS are unknown, some have hypothesised that it involves disinhibition, i.e. a reduction in gamma-Aminobutyric acid (GABA) activity. In this study we addressed this hypothesis by using edited magnetic resonance spectroscopy (MRS) to determine sensorimotor GABA and glutamate concentrations in 16 humans with CRPS and 30 matched controls and the relationship of these concentrations with tactile acuity. We found that individuals with upper limb CRPS displayed reduced tactile acuity in the painful hand compared with the non-painful hand and pain-free controls. Despite this acuity deficit, CRPS was not associated with altered GABA or glutamate concentrations within the sensorimotor cortex on either the side that represents the affected or unaffected hand. Furthermore, there was no significant relationship between sensorimotor GABA or glutamate concentrations and tactile acuity in CRPS or control subjects. Although our sample was small, these data suggest that CRPS is not associated with altered total sensorimotor GABA or glutamate concentrations. Whilst these results are at odds with the sensorimotor cortex disinhibition hypothesis, it is possible that GABAergic mechanisms other than total GABA concentration may contribute to such disinhibition. Complex regional pain syndrome is a debilitating chronic pain disorder that usually affects the limbs. It is associated with altered sensorimotor cortex function including reorganisation and reduced tactile acuity, which are thought to result from reduced on-going inhibition. However, we found that this pain condition is not associated with reduced on-going sensorimotor inhibition in the form of gamma-Aminobutyric acid concentration, the major inhibitory neurotransmitter in the brain. These findings strongly suggest that changes in sensorimotor function in individuals with complex regional pain syndrome are explained by factors other than neurotransmitter concentration.

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Neck pain and headache following whiplash injury: a systematic review and meta-analysis.

Neck pain and headache are two of the most common complications of whiplash injury. Therefore, we performed a systematic literature search on PubMed and Embase for publications reporting on the prevalence of neck pain and headache following whiplash injury. The literature search identified 2,709 citations of which 44 contained relevant original data. Of these, 27 studies provided data for the quantitative analysis. For non-population-based studies, the present meta-analysis showed that a pooled relative frequency of neck pain was 84% CI (68-95%) and a pooled relative frequency of headache was 60% (46-73%), within 7 days following whiplash injury. At 12 months post-injury, 38% (32-45%) of patients with whiplash still experienced neck pain, while 38% (18-60%) of whiplash patients reported headache at the same time interval post-injury. However, we also found considerable heterogeneity among studies with I-values ranging from 89-98% for the aforementioned meta-analyses. We believe that the considerable heterogeneity among studies underscores the need for clear-cut definitions of whiplash injury and standardized reporting guidelines for post-whiplash sequelae such as neck pain and headache. Future studies should seek to optimize these aspects paving the way for a better understanding of the clinical characteristics and natural course of whiplash-associated sequelae.

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Brain networks and endogenous pain inhibition are modulated by age and sex in healthy rats.

Endogenous pain inhibition is less efficient in chronic pain patients. Diffuse noxious inhibitory control (DNIC), a form of endogenous pain inhibition, is compromised in women and older people, making them more vulnerable to chronic pain. However, the underlying mechanisms remain unclear. Here, we used a capsaicin-induced DNIC test and resting state functional MRI to investigate the impact of aging and sex on endogenous pain inhibition and associated brain circuitries in healthy rats. We found that DNIC was less efficient in young females compared to young males. DNIC response was lost in old rats of both sexes, but the brain networks engaged during DNIC differed in a sex-dependent manner. Young males had the most efficient analgesia with the strongest connectivity between anterior cingulate cortex (ACC) and periaqueductal gray (PAG). The reduced efficiency of DNIC in young females appeared to be driven by a widespread brain connectivity. Old males showed increased connectivity between PAG, raphe nuclei, pontine reticular nucleus and hippocampus, which may not be dependent on connections to ACC, while old females showed increased connectivity between ACC, PAG and more limbic regions. These findings suggest that distinct brain circuitries including the limbic system may contribute to higher susceptibility to pain modulatory deficits in the elderly population, and sex may be a risk factor for developing age-related chronic pain.

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c-Jun/p38MAPK/ASIC3 pathways specifically activated by NGF through TrkA is crucial for mechanical allodynia development.

Mechanical allodynia is a cardinal sign of several inflammatory pain disorders where Nerve Growth Factor, a prototypic neurotrophin, plays a crucial role by binding to TrkA receptors. Here, we took the advantage of our generated knock-in mouse model expressing a chimeric TrkA/TrkC receptor that seems to not specifically develop mechanical allodynia following inflammation, to identify the TrkA downstream pathways involved in this phenomenon. We confirmed and extended that disrupting TrkA specific pathways leads to a specific deficit in mechanical hypersensitivity development following somatic (systemic NGF administration and paw incision) and to a lesser extent, visceral injuries. Despite a deficit in thin, mainly peptidergic, fibres innervation in TrkAC mice, thermal hyperalgesia development was not different from WT mice. Inflammatory reaction (oedema, IL-6 content), pain behaviours following intraplantar capsaicin as well as TRPV1 calcium imaging response of DRG neurons were similar between TrkAC and WT mice. This deficiency in mechanical allodynia development in TrkAC mice is likely due to the alteration of the expression of different TrkA transduction pathways (i.e. Akt, p38 MAPK and c-Jun) especially p38 MAPK, in the DRG cell bodies, ultimately leading to an alteration of at least, ASIC3 channel overexpression, known to participate in nociceptor mechanosensory function.

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Assessing peripheral fibers, pain sensitivity, central sensitization, and descending inhibition in Native Americans: main findings from the Oklahoma Study of Native American Pain Risk.

Native Americans (NAs) have a higher prevalence of chronic pain than other U.S. racial/ethnic groups, but there have been few attempts to understand the mechanisms of this pain disparity. This study used a comprehensive battery of laboratory tasks to assess peripheral fiber function (cool/warm detection thresholds), pain sensitivity (eg, thresholds/tolerances), central sensitization (eg, temporal summation), and pain inhibition (conditioned pain modulation) in healthy, pain-free adults (N = 155 NAs, N = 150 non-Hispanic Whites [NHWs]). Multiple pain stimulus modalities were used (eg, cold, heat, pressure, ischemic, and electric), and subjective (eg, pain ratings and pain tolerance) and physiological (eg, nociceptive flexion reflex) outcomes were measured. There were no group differences on any measure, except that NAs had lower cold-pressor pain thresholds and tolerances, indicating greater pain sensitivity than NHWs. These findings suggest that there are no group differences between healthy NAs and NHWs on peripheral fiber function, central sensitization, or central pain inhibition, but NAs may have greater sensitivity to cold pain. Future studies are needed to examine potential within-group factors that might contribute to NA pain risk.

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Does experimentally induced pain-related fear influence central and peripheral movement preparation in healthy people and low back pain patients?

Non-specific chronic low back pain (CLBP) is a multifactorial disorder. Pain-related fear and altered movement preparation are considered to be key factors in the chronification process. Interactions between both have been hypothesized, but studies examining the influence of situational fear on movement preparation in low back pain (LBP) are wanting, as well as studies differentiating between recurrent LBP (RLBP) and CLBP. Therefore, this study examined whether experimentally induced pain-related fear influences movement preparation. In healthy controls (n=32), RLBP (n=31) and CLBP (n=30) patients central and peripheral measures of movement preparation were assessed by concurrently measuring trunk muscle anticipatory postural adjustments (APA) with EMG and Contingent Negative Variation (CNV) with EEG during performance of rapid arm movements (RAM). Two conditions were compared, one without (no fear) and one with (fear) possibility of painful stimulation to the back during RAM. Visual analogue scales were used to assess pain-related expectations/fear in both conditions. The experimentally induced fear of pain during movement performance led to an increase in CNV-amplitude, which was similar in all three groups. Concerning APAs no effects of fear were found, but group differences with generally delayed APAs in CLBP compared to controls and RLBP patients were evident. These results suggest that with fear an attentional redirection towards more conscious central movement preparation strategies occurs. Furthermore, differences in movement preparation in RLBP and CLBP patients exist, which could explain why RLBP patients have more recovery capabilities than CLBP.

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Supraspinal Opioid Circuits Differentially Modulate Spinal Neuronal Responses in Neuropathic Rats.

Descending control from supraspinal neuronal networks onto spinal cord neurons can modulate nociceptionEndogenous opioids in these brain circuits participate in pain modulationA differential opioidergic role for brain nuclei involved in supraspinal pain modulation has not been previously reported WHAT THIS ARTICLE TELLS US THAT IS NEW: In vivo electrophysiologic recordings from the dorsal horn of the spinal cord in male rats reveal differential effects of morphine at the anterior cingulate cortex, right amygdala, and the ventromedial medulla on evoked pain responsesThese data differentiate supraspinal opioid circuit regulation of spinal nociceptive processing and suggest that the regulation of sensory and affective components of pain are likely separate BACKGROUND:: The anterior cingulate cortex and central nucleus of the amygdala connect widely with brainstem nuclei involved in descending modulation, including the rostral ventromedial medulla. Endogenous opioids in these circuits participate in pain modulation. The hypothesis was that a differential opioidergic role for the brain nuclei listed in regulation of spinal neuronal responses because separable effects on pain behaviors in awake animals were previously observed.

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Lasmiditan inhibits calcitonin gene-related peptide release in the rodent trigeminovascular system.

Migraine headache pathophysiology involves trigeminovascular system activation, calcitonin gene-related peptide (CGRP) release and dysfunctional nociceptive transmission. Triptans are 5-HT1B/1D/(1F) receptor agonists that prejunctionally inhibit trigeminal CGRP release, but their vasoconstrictor properties limit their use in migraine patients with cardiovascular disease. In contrast, lasmiditan is a novel antimigraine and selective 5-HT1F receptor agonist devoid of vasoconstrictor properties. On this basis, the present study has investigated the modulation of trigeminal CGRP release by lasmiditan.For this purpose, we have comparatively analysed the inhibition of several components of the trigeminovascular system induced by lasmiditan and sumatriptan through: ex vivo KCl-induced CGRP release from isolated dura mater, trigeminal ganglion and trigeminal nucleus caudalis of mice; and in vivo dural vasodilation in the rat closed-cranial window model induced by endogenous (electrical stimulation, capsaicin) and exogenous CGRP.The ex vivo release of CGRP was similarly inhibited by sumatriptan and lasmiditan in all trigeminovascular system components. In vivo, i.v. lasmiditan or higher doses of sumatriptan significantly attenuated the vasodilatory responses to endogenous CGRP release, but not exogenous CGRP effects. These data suggest that lasmiditan prejunctionally inhibits CGRP release in peripheral and central trigeminal nerve terminals. Since lasmiditan is a lipophilic drug that crosses the blood-brain barrier, additional central sites of action remain to be determined.

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Biased Signaling of the G-Protein-Coupled Receptor βAR Is Governed by Conformational Exchange Kinetics.

G-protein-coupled receptors (GPCRs) mediate a wide range of human physiological functions by transducing extracellular ligand binding events into intracellular responses. GPCRs can activate parallel, independent signaling pathways mediated by G proteins or β-arrestins. Whereas "balanced" agonists activate both pathways equally, "biased" agonists dominantly activate one pathway, which is of interest for designing GPCR-targeting drugs because it may mitigate undesirable side effects. Previous studies demonstrated that β-arrestin activation is associated with transmembrane helix VII (TM VII) of GPCRs. Here, single-molecule fluorescence spectroscopy with the β-adrenergic receptor (βAR) in the ligand-free state showed that TM VII spontaneously fluctuates between one inactive and one active-like conformation. The presence of the β-arrestin-biased agonist isoetharine prolongs the dwell time of TM VII in the active-like conformation compared with the balanced agonist formoterol, suggesting that ligands can induce signaling bias by modulating the kinetics of receptor conformational exchange.

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Reorganization of the Primate Dorsal Horn in Response to a Deafferentation Lesion Affecting Hand Function.

The loss of sensory input following a spinal deafferentation injury can be debilitating, and this is especially true in primates when the hand is involved. While significant recovery of function occurs, little is currently understood about the reorganization of the neuronal circuitry, particularly within the dorsal horn. This region receives primary afferent input from the periphery, and cortical input via the somatosensory subcomponent of the corticospinal tract (S1 CST), and is critically important in modulating sensory transmission, both in normal and lesioned states. To determine how dorsal horn circuitry alters to facilitate recovery post-injury, we used an established deafferentation lesion model (DRL/DCL – dorsal root/dorsal column) in male monkeys to remove sensory input from just the opposing digits (D1-D3) of one hand. This results in a deficit in fine dexterity that recovers over several months. Electrophysiological mapping, tract tracing, and immunolabeling techniques were combined to delineate specific changes to dorsal horn input circuitry. Our main findings show that (1) there is complementary sprouting of the primary afferent and S1 CST populations into an overlapping region of the reorganizing dorsal horn, (2) S1 CST and primary afferent inputs connect in different ways within this region to facilitate sensory integration (3) there is a loss of larger S1 CST terminal boutons in the affected dorsal horn, but no change in the size profile of the spared/sprouted primary afferent terminal boutons post-lesion. Understanding such changes helps to inform new and targeted therapies that best promote recovery.Spinal injuries that remove sensation from the hand, can be debilitating, though functional recovery does occur. We examined changes to the neuronal circuitry of the dorsal horn in monkeys following a lesion that deafferented three digits of one hand. Little is understood about dorsal horn circuitry, despite the fact that this region loses most of its normal input after such an injury, and is clearly a major focus of reorganization. We found that both the spared primary afferents and somatosensory corticospinal efferents sprouted in an overlapping region of the dorsal horn after injury, and that larger (presumably faster) corticospinal terminals are lost, suggesting a significantly altered cortical modulation of primary afferents. Understanding this changing circuitry is important for designing targeted therapies.

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Threat prediction from schemas as a source of bias in pain perception.

Our sensory impressions of pain are generally thought to represent the noxious properties of an agent but can be influenced by the predicted level of threat. Predictions can be sourced from higher-order cognitive processes such as schemas, but the extent to which schemas can influence pain perception relative to bottom-up sensory inputs and the underlying neural underpinnings of such phenomenon are unclear. Here we investigate how threat predictions generated from learning a cognitive schema leads to inaccurate sensory impressions of the pain stimulus. Healthy men and women participants first detected a linear association between cue-values and stimulus intensity and rated pain to reflect the linear schema when compared with un-cued heat stimuli. The effect of bias on pain ratings was reduced when prediction errors increased, but pain perception was only partially updated when measured against stepped increases in prediction errors. Cognitive, striatal, and sensory regions graded their responses to changes in predicted threat despite of the prediction errors (p<0.05, corrected). Individuals with more catastrophic thinking about pain and with low mindfulness were significantly more reliant on the schema than on the sensory evidence from the pain stimulus. These behavioral differences mapped to variability in responses of the striatum and ventral medial prefrontal cortex. Thus, this study demonstrates a significant role of higher-order schemas on pain perception and indicates that pain perception is biased more towards predictions and less towards nociceptive inputs in individuals who report less mindfulness and more fear of pain.Significance statement: This study demonstrates that threat predictions generated from cognitive schemas continue to influence pain perception despite of increasing prediction errors arising in pain pathways. Individuals first formed a cognitive schema of linearity in the relationship between the cued threat value and the stimulus intensity. Subsequently, the linearity was reduced gradually, and participants partially updated their evaluations of pain in relation with the stepped increases in prediction errors. Individuals who continued to rate pain based more on the predicted threat than on changes in nociceptive inputs reported high pain catastrophizing and less mindful-awareness scores. These two affects mapped to activity in the ventral and dorsal striatum respectively. These findings direct us to a significant role of top-down processes in pain perception.

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Gut nociceptors: sentinels promoting host defense.

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Acid and inflammatory sensitisation of naked mole-rat colonic afferent nerves.

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HLA class I alleles are associated with clinic-based migraine and increased risks of chronic migraine and medication overuse.

We aimed to evaluate associations of human leukocyte antigen variants with migraine or headache in hospital and population-based settings.

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Identification of a sacral, visceral sensory transcriptome in embryonic and adult mice.

Visceral sensory neurons encode distinct sensations from healthy organs and initiate pain states that are resistant to common analgesics. Transcriptome analysis is transforming our understanding of sensory neuron subtypes but has generally focused on somatic sensory neurons or the total population of neurons in which visceral neurons form the minority. Our aim was to define transcripts specifically expressed by sacral visceral sensory neurons, as a step towards understanding the unique biology of these neurons and potentially leading to identification of new analgesic targets for pelvic visceral pain. Our strategy was to identify genes differentially expressed between sacral dorsal root ganglia (DRG) that include somatic neurons and sacral visceral neurons, and adjacent lumbar DRG that comprise exclusively of somatic sensory neurons. This was performed in adult and E18.5 male and female mice. By developing a method to restrict analyses to nociceptive Trpv1 neurons, a larger group of genes were detected as differentially expressed between spinal levels. We identified many novel genes that had not previously been associated with pelvic visceral sensation or nociception. Limited sex differences were detected across the transcriptome of sensory ganglia, but more were revealed in sacral levels and especially in Trpv1 nociceptive neurons. These data will facilitate development of new tools to modify mature and developing sensory neurons and nociceptive pathways. In this study of mouse dorsal root ganglia, we have identified numerous features of sensory neurons that vary between lumbar and sacral spinal levels and that are potentially involved in unique physiology and pathophysiology of visceral sensation and pain. We further identify maturational components of this sacral visceral transcriptome by comparing data from embryonic and adult mice. There are limited sex differences across the transcriptome of embryonic or adult sensory ganglia, but in adults these can be revealed in sacral levels and especially in Trpv1 nociceptive neurons. These data sets will encourage identification of new tools to modify mature or developing sensory neurons and adult nociceptive pathways.

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Let it be: Mindful-acceptance down-regulates pain and negative emotion.

Mindfulness training ameliorates clinical and self-report measures of depression and chronic pain, but its use as an emotion regulation strategy – in individuals who do not meditate – remains understudied. As such, whether it (a) down-regulates early affective brain processes and (b) depends on cognitive control systems remains unclear. We exposed meditation-naïve participants to two kinds of stimuli: negative vs. neutral images and painful vs. warm temperatures. On alternating blocks, we asked participants to either react naturally or exercise mindful-acceptance. Emotion regulation using mindful-acceptance was associated with reductions in reported pain and negative affect, reduced amygdala responses to negative images, and reduced heat-evoked responses in medial and lateral pain systems. Critically, mindful-acceptance significantly reduced activity in a distributed, a-priori neurologic signature that is sensitive and specific to experimentally-induced pain. In addition, these changes occurred in the absence of detectable increases in prefrontal control systems. The findings support the idea that momentary mindful-acceptance regulates emotional intensity by changing initial appraisals of the affective significance of stimuli, which has consequences for clinical treatment of pain and emotion.

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Cupping for patients with chronic pain: a systematic review and meta-analysis.

There is a growing interest in non-pharmacological pain treatment options such as cupping. This meta-analysis aimed to assess the effectiveness and safety of cupping in chronic pain. PubMed, Cochrane Library, and Scopus were searched through November 2018 for randomized controlled trials on effects of cupping on pain intensity and disability in patients with chronic pain. Risk of bias was assessed using the Cochrane risk-of-bias tool. Of the 18 included trials (n=1,172), most were limited by clinical heterogeneity and risk of bias. Meta-analyses found large short-term effects of cupping on pain intensity compared to no treatment (standardized mean difference [SMD]=-1.03; 95% confidence interval [CI]=-1.41,-0.65), but no significant effects compared to sham cupping (SDM=-0.27; 95%CI=-0.58,0.05) or other active treatment (SMD=-0.24; 95%CI=-0.57,0.09). For disability, there were medium-sized short-term effects of cupping compared to no treatment (SMD=-0.66; 95%CI=-0.99,-0.34), and compared to other active treatments (SMD=-0.52; 95%CI=-1.03,-0.0028), but not compared to sham cupping (SMD=-0.26; 95%CI=-0.57, 0.05). Adverse events were more frequent among patients treated with cupping compared to no treatment; differences compared to sham cupping or other active treatment were not statistically significant. Cupping might be a treatment option for chronic pain, but the evidence is still limited by the clinical heterogeneity and risk of bias. Perspective: This article presents the results of a meta-analysis aimed to assess the effectiveness and safety of cupping with chronic pain. The results suggest that cupping might be a treatment option; however, the evidence is still limited due to methodical limitations of the included trials. High quality trials seem warranted.

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Five-year Pain Intensity and Treatment Trajectories of Post-9/11 Veterans with Mild Traumatic Brain Injury.

Pain is a pervasive problem that affects nearly half of the U.S. Veterans deployed in support of the Global War on Terror (Post-9/11 Veterans) and over half of the Post-9/11 Veterans with diagnosed traumatic brain injury (TBI). The goal of the current study was to identify pain phenotypes based on distinct longitudinal patterns of pain scores in light of pain treatment among Post-9/11 Veterans over five years of care using latent growth mixture analysis stratified by TBI status. Five pain phenotypes emerged: (1) simple low impact stable pain, (2) complex low impact stable pain, (3) complex low impact worsening pain, (4) complex moderate impact worsening pain, and (5) complex high impact stable pain. Baseline pain scores and slopes were significantly higher in Veterans with mild TBI for some phenotypes. The mild TBI cohort was younger, had more men, more whites, less blacks, less education, more unmarried, more Marines and Army, more active duty in comparison to the no TBI cohort. Distinct trajectories in pain treatment were apparent among the pain intensity subgroups. Perspective: The complexity of pain in patients with mTBI is categorically different than those with no TBI. Pain in patients with mTBI is heterogeneous with distinct phenotypes which may explain poor outcomes in this group. Identification of the individual differences may have a significant impact on the success of interventions.

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Data-science-based subgroup analysis of persistent pain during 3 years after breast cancer surgery.

Persistent pain extending beyond 6 months after breast cancer surgery when adjuvant therapies have ended is a recognised phenomenon. The evolution of postsurgery pain is therefore of interest for future patient management in terms of possible prognoses for distinct groups of patients to enable better patient information.

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Can slow deep breathing reduce pain? An experimental study exploring mechanisms.

Slow deep breathing (SDB) is commonly employed in the management of pain, but the underlying mechanisms remain equivocal. This study sought to investigate effects of instructed breathing patterns on experimental heat pain and to explore possible mechanisms of action. In a within-subject experimental design, healthy volunteers (n = 48) performed four breathing patterns: 1) unpaced breathing (UB), 2) paced breathing at the participant's spontaneous breathing frequency (PB), 3) SDB at six breaths per minute with a high inspiration/expiration ratio (SDB-H), and 4) SDB at six breaths per minute with a low inspiration/expiration ratio (SDB-L). During presentation of each breathing pattern, participants received painful heat stimuli of three different temperatures and rated each stimulus on pain intensity. Respiration, heart rate, and blood pressure were recorded. Compared to UB, participants reported less intense pain during each of the three instructed breathing patterns. Among the instructed breathing patterns, pain did not differ between PB and SDB-H, and SDB-L attenuated pain more than the PB and SDB-H patterns. The latter effect was paralleled by greater blood pressure variability and baroreflex effectiveness index during SDB-L. Cardiovascular changes did not mediate the observed effects of breathing patterns on pain. Perspective: SDB is more efficacious to attenuate pain when breathing is paced at a slow rhythm with an expiration that is long relative to inspiration, but the underlying mechanisms remain to be elucidated.

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Adherence to Consolidated Standards of Reporting Trials (CONSORT) Guidelines for Reporting Safety Outcomes in Trials of Medical Cannabis and Cannabis-based Medicines for Chronic Noncancer Pain: A Systematic Review.

Current treatments for chronic pain have limited effectiveness and tolerability. With growing interest in the potential of cannabinoids, there is a need to inform risk-benefit considerations. Thus, this focused systematic review assesses the quality of safety assessment and reporting in chronic noncancer pain cannabinoid trials.

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The Interplay of Parent and Child Coping Responses in Understanding Child Functioning in the Context of Living with a Parent with or Without Chronic Pain.

Pain problems tend to run in families and children of individuals with chronic pain (ICPs) have been found to report lower functioning. Drawing upon a social learning perspective, the current study examined how diverse maternal pain coping responses (i.e., pain catastrophizing and distraction) may, via corresponding child pain coping responses, act as a vulnerability or protective factor for child functioning in the context of parental chronic pain (CP).

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ASIC3 blockade inhibits durovascular and nitric oxide-mediated trigeminal pain.

There is a major unmet need to develop new therapies for migraine. We have previously demonstrated the therapeutic potential of the acid sensing ion channel (ASIC) blockade in migraine, via an ASIC1 mechanism. ASIC3 is expressed in the trigeminal ganglion and its response is potentiated by nitric oxide that can trigger migraine attacks in patients, and thus we sought to explore the potential therapeutic effect of ASIC3 blockade in migraine.

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One step closer to alleviating uraemic pruritus.

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Practice review: Evidence-based and effective management of pain in patients with advanced cancer.

Pain of a moderate or severe intensity affects over half of patients with advanced cancer and remains undertreated in at least one-third of these patients.

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Distinct roles for innexin gap junctions and hemichannels in mechanosensation.

Mechanosensation is central to a wide range of functions, including tactile and pain perception, hearing, proprioception, and control of blood pressure, but identifying the molecules underlying mechanotransduction has proved challenging. In , the avoidance response to gentle body touch is mediated by 6 touch receptor neurons (TRNs), and is dependent on MEC-4, a DEG/ENaC channel. We show that hemichannels containing the innexin protein UNC-7 are also essential for gentle touch in the TRNs, as well as harsh touch in both the TRNs and the PVD nociceptors. UNC-7 and MEC-4 do not colocalize, suggesting that their roles in mechanosensory transduction are independent. Heterologous expression of in touch-insensitive chemosensory neurons confers ectopic touch sensitivity, indicating a specific role for UNC-7 hemichannels in mechanosensation. The touch defect can be rescued by the homologous mouse gene gene, thus, innexin/pannexin proteins may play broadly conserved roles in neuronal mechanotransduction.

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Characterization of Ubrogepant: A Potent and Selective Antagonist of the Human Calcitonin Gene‒Related Peptide Receptor.

A growing body of evidence has implicated the calcitonin gene-related peptide (CGRP) receptors in migraine pathophysiology. With the recent approval of monoclonal antibodies targeting CGRP or the CGRP receptor, the inhibition of CGRP-mediated signaling has emerged as a promising approach for preventive treatments of migraine in adults. However, there are no small-molecule anti-CGRP treatments available for treating migraine. The current studies aimed to characterize the pharmacologic properties of ubrogepant, an orally bioavailable, CGRP receptor antagonist for the acute treatment of migraine. In a series of ligand binding assays, ubrogepant exhibited a high binding affinity for native (=0.067 nM) and cloned human (=0.070 nM) and rhesus CGRP receptors (=0.079 nM), with relatively lower affinities for CGRP receptors from rat, mouse, rabbit and dog. In functional assays, ubrogepant potently blocked human α-CGRP stimulated cAMP response (IC of 0.08 nM) and exhibited highly selective antagonist activity for the CGRP receptor compared with other members of the human calcitonin receptor family. Furthermore, the in vivo CGRP receptor antagonist activity of ubrogepant was evaluated in a pharmacodynamic model of capsaicin-induced dermal vasodilation (CIDV) in rhesus monkeys and humans. Results demonstrated that ubrogepant produced concentration-dependent inhibition of CIDV with a mean EC of 3.2 and 2.6 nM in rhesus monkeys and humans, respectively. Brain penetration studies with ubrogepant in monkeys showed a CSF/plasma ratio of 0.03 and low CGRP receptor occupancy. In summary, ubrogepant is a competitive antagonist with high affinity, potency, and selectivity for the human CGRP receptor. SIGNIFICANCE STATEMENT: Ubrogepant is a potent, selective, orally delivered, small-molecule competitive antagonist of the human calcitonin generelated peptide receptor. In vivo studies using a pharmacodynamic model of capsaicin-induced dermal vasodilation (CIDV) in rhesus monkeys and humans demonstrated that ubrogepant produced concentration-dependent inhibition of CIDV, indicating a predictable pharmacokinetic-pharmacodynamic relationship.

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Centralized pain and pain catastrophizing mediate the association between lifetime abuse history and self-reported pain medication side effects.

Self-reported side effects of pain medication are important determinants of treatment course that can affect patient adherence, medication discontinuation and physician decisions. Yet, few studies have investigated patient-level predictors of self-reported pain medication side effects. The present study sought to fill this gap by exploring the impact of physical or sexual abuse history on self-reported pain medication side effects and considered a mediation model in which those effects are transmitted through a centralized pain phenotype and pain catastrophizing.

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Improving opioid guideline adherence: evaluation of a multifaceted, theory-informed pilot intervention for family physicians.

Opioid-related deaths continue to increase in North America, an epidemic that was initiated by high rates of opioid prescribing. We designed a multifaceted, theory-informed Opioid Self-Assessment (OSA) package, to increase adherence to the Canadian Opioid Guideline among family physicians. This study aimed to assess changes in Canadian family physicians' knowledge and practices after completing the OSA package.

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Multicenter Perioperative Outcomes Group Enhanced Observation Study Postoperative Pain Profiles, Analgesic Use, and Transition to Chronic Pain and Excessive and Prolonged Opioid Use Patterns Methodology.

To study the impact of anesthesia opioid-related outcomes and acute and chronic postsurgical pain, we organized a multicenter study that comprehensively combined detailed perioperative data elements from multiple institutions. By combining pre- and postoperative patient-reported outcomes with automatically extracted high-resolution intraoperative data obtained through the Multicenter Perioperative Outcomes Group (MPOG), the authors sought to describe the impact of patient characteristics, preoperative psychological factors, surgical procedure, anesthetic course, postoperative pain management, and postdischarge pain management on postdischarge pain profiles and opioid consumption patterns. This study is unique in that it utilized multicenter prospective data collection using a digital case report form integrated with the MPOG framework and database. Therefore, the study serves as a model for future studies using this innovative method. Full results will be reported in future articles; the purpose of this article is to describe the methods of this study.

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Interventions for chronic pruritus of unknown origin.

Pruritus is a sensation that leads to the desire to scratch; its origin is unknown in 8% to 15% of affected patients. The prevalence of chronic pruritus of unknown origin (CPUO) in individuals with generalised pruritus ranges from 3.6% to 44.5%, with highest prevalence among the elderly. When the origin of pruritus is known, its management may be straightforward if an effective treatment for the causal disease is available. Treatment of CPUO is particularly difficult due to its unknown pathophysiology.

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An evaluation of the anti-hyperalgesic effects of cannabidiolic acid-methyl ester (CBDA-ME) in a preclinical model of peripheral neuropathic pain.

Chronic neuropathic pain (NEP) is associated with growing therapeutic cannabis use. To promote quality of life without psychotropic effects, cannabinoids other than Δ9-tetrahydrocannabidiol, including cannabidiol and its precursor cannabidiolic acid (CBDA), are being evaluated. Due to its instability, CBDA has been understudied, particularly as an anti-nociceptive agent. Adding a methyl ester group (CBDA-ME) significantly enhances its stability, facilitating analyses of its analgesic effects in vivo. This study examines early treatment efficacy of CBDA-ME in a rat model of peripherally induced NEP and evaluates sex as a biological variable.

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Drivers of the opioid crisis: An appraisal of financial conflicts of interest in clinical practice guideline panels at the peak of opioid prescribing.

Starting in the late 1990s, the pharmaceutical industry sought to increase prescribing of opioids for chronic non-cancer pain. Influencing the content of clinical practice guidelines may have been one strategy industry employed. In this study we assessed potential risk of bias from financial conflicts of interest with the pharmaceutical industry in guidelines for opioid prescribing for chronic non-cancer pain published between 2007 and 2013, the peak of opioid prescribing.

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Serum Inflammatory Markers in Patients with Knee Osteoarthritis: A Proteomic Approach.

Osteoarthritis (OA) is known to be a slowly progressive disease that alters all tissue compartments of the joint involved with a characteristic degradation of the cartilage, bone remodeling, and inflammation. One of the prominent symptoms in OA patients is pain, but a few radiological, inflammatory or structurally related biomarkers have shown little if any associations to pain. This study aimed to assess serum levels of 92 markers involved in inflammatory pathways in patients with knee OA (KOA) and evaluate their possible associations with the clinical pain intensity.

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The Relationship between Clinical and Quantitative Measures of Pain Sensitization in Knee Osteoarthritis.

Pain sensitization in knee osteoarthritis is associated with greater symptom severity and poorer clinical outcomes. Measures which identify pain sensitization and are accessible to use in clinical practice have been suggested to enable more targeted treatments. This merits further investigation. This study examines the relationship between Quantitative Sensory Testing (QST) and clinical measures of pain sensitization in people with knee osteoarthritis.

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Blockade of BDNF Signaling Attenuates Chronic Visceral Hypersensitivity in an IBS-like Rat Model.

Irritable bowel syndrome (IBS) is a common functional disease characterized by chronic abdominal pain and changes in bowel movements. Effective therapy for visceral hypersensitivity in IBS patients remains challenging. This study investigated the roles of brain-derived neurotrophic factor (BDNF) and tyrosine kinase receptor B (TrkB) and the effect of ANA-12 (a selective antagonist of TrkB) on chronic visceral hypersensitivity in an IBS-like rat model.

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Intravenous Endothelin-1 Infusion Does Not Induce Aura or Headache in Migraine Patients With Aura.

To investigate whether intravenously infused provokes migraine aura and migraine headache in migraine patients with aura.

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Workforce Gap Analysis in the Field of Headache Medicine in the United States.

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Inflammation without pain: Immune-derived opioids hold the key.

Visceral pain is commonly associated with acute or remitting inflammatory bowel disease (IBD). In marked contrast, chronic IBD is often painless, even in the presence of active inflammation. This suggests that inflammation in itself is insufficient to sustain altered nociceptive signaling and raises the possibility that there is an endogenous analgesic system in effect in chronic disease. A new study by Basso et al. published in this issue of Neurogastroenterology & Motility provides additional support for an immune-mediated mechanism that suppresses visceral hypersensitivity. The authors examined visceral pain in the IL-10-piroxicam model of chronic colitis, which differs from other experimental IBD models in that it involves immune suppression. During active inflammation, responses by these mice to graded increases in colorectal distension were equivalent to healthy controls, consistent with normal afferent signaling. However, treatment with a peripherally restricted opioid receptor antagonist resulted in marked visceral hypersensitivity to the same stimuli. This effect was attributed to the production of endogenous opioids by colitogenic CD4 T cells present in the mucosa. This mini-review provides a brief overview of analgesia by immune-derived opioids under inflammatory conditions and highlights how the work of Basso et al. contributes to this area of research. Potential pharmacological approaches to harness or mimic this system are provided. These strategies may prove to be an effective means through which targeted and sustained relief of IBD pain may be achieved.

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Comparative Effectiveness of Embedded Mental Health Services in Pain Management Clinics vs Standard Care.

Embedded behavioral medicine services are a common component of multidisciplinary chronic pain treatment programs. However, few studies have studied whether these services are associated with improved treatment outcomes.

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Emerging concepts on the use of ketamine for chronic pain.

: The use of ketamine infusions for chronic pain has surged, with utilization exceeding the proliferation of knowledge. A proposed mechanism for the long-term benefit in chronic pain is that ketamine may alter the affective-motivational component of pain.: In this review, we discuss the classification and various dimensions of pain, and explore the effects of ketamine on different pain categories and components. The relationship between ketamine's action at the NMDA receptor, the development of chronic pain, and the its possible role in preventing the persistence of pain are examined. We also summarize animal models evaluating the antinociceptive effects of ketamine and risk mitigation strategies of ketamine-associated side effects.: Although ketamine exerts most of its analgesic effects via the NMDA receptor, recent evidence suggests that other receptors such as AMPA, and active metabolites such as nor-ketamine, may also play a role in pain relief and alleviation of depression. Data from clinical studies performed in patients with chronic pain and depression, and the observation that ketamine's analgesic benefits outlast its effects on quantitative sensory testing, suggest that the enduring effects on chronic pain may be predominantly due ketamine's ability to modulate the affective-motivational dimension of pain.

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Intrathecally administered perampanel alleviates neuropathic and inflammatory pain in rats.

Chronic pain conditions such as neuropathic pain and persistent inflammatory pain are difficult to manage. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors modulate nociceptive processing at the spinal dorsal horn. Previous studies have shown that intrathecal AMPA receptor antagonists exert antinociception in various pain states. Perampanel is a selective, noncompetitive inhibitor of the AMPA receptor and used clinically as an antiepileptic drug. Little is known about antinociceptive action of perampanel in the spinal cord. Here, we explored whether intrathecal perampanel attenuates neuropathic and inflammatory pain. A chronic constriction injury (CCI) to the sciatic nerve was induced in male Sprague-Dawley rats. We evaluated the effects of intrathecal perampanel (10, 30, or 100 μg) on mechanical and cold hyperalgesia using the electronic von Frey and cold plate tests, respectively. Normal rats were assessed in terms of inflammatory nociception using the formalin test, and motor function employing the rotarod test. In the CCI rats, spinally applied perampanel inhibited mechanical and cold hyperalgesia dose-dependently. In normal rats, perampanel remarkably suppressed the early- and late-phase responses in the formalin test, and it weakly affected motor performance for a short period at the highest dose. These results suggest that perampanel exerts antinociceptive actions on neuropathic and persistent inflammatory pain in the spinal cord. Perampanel may be safe and beneficial remedy for patients with such pain conditions. In addition, AMPA receptor can be a promising target for treatment of chronic pain.

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Volatile anaesthetics inhibit the thermosensitive nociceptor ion channel transient receptor potential melastatin 3 (TRPM3).

Volatile anaesthetics (VAs) are the most widely used compounds to induce reversible loss of consciousness and maintain general anaesthesia during surgical interventions. Although the mechanism of their action is not yet fully understood, it is generally believed, that VAs depress central nervous system functions mainly through modulation of ion channels in the neuronal membrane, including 2-pore-domain K+ channels, GABA and NMDA receptors. Recent research also reported their action on nociceptive and thermosensitive TRP channels expressed in the peripheral nervous system, including TRPV1, TRPA1, and TRPM8. Here, we investigated the effect of VAs on TRPM3, a less characterized member of the thermosensitive TRP channels playing a central role in noxious heat sensation.

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Adjunctive effect of the serotonin 5-HT receptor agonist lorcaserin on opioid-induced antinociception in mice.

Opioid-sparing adjuncts are treatments that aim to reduce the overall dose of opioids needed to achieve analgesia, hence decreasing the burden of side effects through alternative mechanisms of action. Lorcaserin is a serotonin 5-HT receptor (5-HTR) agonist that has recently been reported to reduce abuse-related effects of the opioid analgesic oxycodone. The goal of our studies was to evaluate the effects of adjunctive lorcaserin on opioid-induced analgesic-like behavior using the tail-flick reflex (TFR) test as a mouse model of acute thermal nociception. We show that whereas subcutaneous (s.c.) administration of lorcaserin alone was inactive on the TFR test, adjunctive lorcaserin (s.c.) significantly increased the potency of oxycodone as an antinociceptive drug. This effect was prevented by the 5-HTR antagonist SB242084. A similar lorcaserin (s.c.)-induced adjunctive phenotype was observed upon administration of the opioid analgesics morphine and fentanyl. Remarkably, we also show that, opposite to the effects observed via s.c. administration, intrathecal (i.t.) administration of lorcaserin alone induced antinociceptive TFR behavior, an effect that was not prevented by the opioid receptor antagonist naloxone. This route of administration (i.t.) also led to a significant augmentation of oxycodone-induced antinociception. Lorcaserin (s.c.) did not alter the brain or blood concentrations of oxycodone, which suggests that its adjunctive effects on opioid-induced antinociception do not depend upon changes in opioid metabolism. Together, these data indicate that lorcaserin-mediated activation of the 5-HTR may represent a new pharmacological approach to augment opioid-induced antinociception.

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Cannabinoids for the Treatment of Chronic Pruritus: A Review.

Medical marijuana is becoming widely available to patients in the U.S. and with recreational marijuana now legalized in many states, patient interest is on the rise. The endocannabinoid system plays an important role in skin homeostasis in addition to broader effects on neurogenic responses such as pruritus and nociception, inflammation, and immune reactions. There are numerous studies of in vitro and animal models that provide insight into the possible mechanisms of cannabinoid modulation on pruritus, with the most evidence behind neuronal modulation of both peripheral itch fibers and centrally-acting cannabinoid receptors. In addition, human studies, while limited due to differences in cannabinoids used, disease models, and delivery method, have consistently shown significant reductions in both scratching and symptomatology in chronic pruritus. Clinical studies that have shown reduction in pruritus in several dermatologic (atopic dermatitis, psoriasis, asteatotic eczema, prurigo nodularis, allergic contact dermatitis) and systemic (uremic pruritus, cholestatic pruritus) diseases. These preliminary human studies warrant controlled trials to confirm the benefit of cannabinoids for treatment of pruritus and to standardize treatment regimens and indications. In patients who have refractory chronic pruritus after standard therapies, cannabinoid formulations may be considered as an adjuvant therapy where it is legal.

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How to study anxiety and depression in rodent models of chronic pain?

Mood disorders such as depression and anxiety are frequently observed in patients suffering from chronic pain. Over time, different tests and models have been developed in rodents to study the anxiodepressive-like consequences of chronic pain. This review describes these pre-clinical tools (models and tests) used for studying behavioural aspects of the comorbid relationship between chronic pain and anxiety and/or major depressive disorder (MDD). Three major types of chronic pain strongly associated with anxiodepressive-like comorbidity as well as their animal models are presented: neuropathic pain, inflammatory pain and fibromyalgia. After a description of chronic pain animal models and of the tests that allows determining nociceptive responses, this review presents and discusses the various behavioural tests that have been used to assess anxiety and depressive-like behaviours in these models of chronic pain. Finally, this review highlights the progress that remains to be made to homogenize the results in the field of pain-induced mood disorders and summarizes the recent advances achieved through these tests and models.

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A Phase 1, Randomized, Open-Label, Safety, Tolerability, and Comparative Bioavailability Study of Intranasal Dihydroergotamine Powder (STS101), Intramuscular Dihydroergotamine Mesylate, and Intranasal DHE Mesylate Spray in Healthy Adult Subjects.

To investigate and compare the safety and the pharmacokinetics of dihydroergotamine (DHE) after administration of intranasal DHE powder (STS101), intranasal DHE spray (Migranal ), and intramuscular (IM) DHE injection in healthy subjects.

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Prognostic factors for improved physical and emotional functioning one year after interdisciplinary rehabilitation in patients with chronic pain: Results from a national quality registry in Sweden.

To investigate prognostic factors for physical and emotional functioning following interdisciplinary multimodal pain rehabilitation, by targeting patients' baseline characteristics and health measures.

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A Pilot Randomized Controlled Trial to Assess the Impact of Motivational Interviewing on Initiating Behavioral Therapy for Migraine.

Relaxation, biofeedback, and cognitive behavioral therapy are evidence-based behavioral therapies for migraine. Despite such efficacy, research shows that only about half of patients initiate behavioral therapy recommended by their headache specialists.

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Dysphasia and Other Higher Cortical Dysfunctions During the Migraine Aura-a Systematic Review of Literature.

Although visual and somatosensory disturbances are the most common migraine aura (MA) symptoms, patients can also experience other symptoms during their MA. The aim of this review is to provide an overview of studies that report symptoms of dysphasia and other higher cortical dysfunctions (HCDs) during MA, as well as to determine the frequency of HCDs.

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Investigating the Effect of Perioperative Chlorzoxazone On Acute Postoperative Pain After Total Hip and Knee Replacement Surgery.

Severe pre- and acute postoperative pain have been associated with development of chronic postoperative pain. Chlorzoxazone (a muscle relaxant) has been suggested to enhance acute postoperative pain recovery but the lack of larger randomized controlled trials have however questioned the continued use. Despite this, chlorzoxazone is still used for acute postoperative pain management following total knee or hip replacement (TKR or THR). The currentrandomized, double blinded, placebo-controlled, parallel group, clinical trial aimed to assess the effect of chlorzoxazone for postoperative pain management following TKR or THR.

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Diabetic neuropathy: what does the future hold?

Frustratingly, disease-modifying treatments for diabetic neuropathy remain elusive. Glycaemic control has a robust effect on preventing neuropathy in individuals with type 1 but not in those with type 2 diabetes, which constitute the vast majority of patients. Encouragingly, recent evidence points to new metabolic risk factors and mechanisms, and thus also at novel disease-modifying strategies, which are desperately needed. Obesity has emerged as the second most important metabolic risk factor for neuropathy (diabetes being the first) from consensus findings of seven observational studies in populations across the world. Moreover, dyslipidaemia and altered sphingolipid metabolism are emergent novel mechanisms of nerve injury that may lead to new targeted therapies. Clinical history and examination remain critical components of an accurate diagnosis of neuropathy. However, skin biopsies and corneal confocal microscopy are promising newer tests that have been used as outcome measures in research studies but have not yet demonstrated clear clinical utility. Given the emergence of obesity as a neuropathy risk factor, exercise and weight loss are potential interventions to treat and/or prevent neuropathy, although evidence supporting exercise currently outweighs data supporting weight loss. Furthermore, a consensus has emerged advocating tricyclic antidepressants, serotonin-noradrenaline (norepinephrine) reuptake inhibitors and gabapentinoids for treating neuropathic pain. Out-of-pocket costs should be considered when prescribing these medications since their efficacy and tolerability are similar. Finally, the downsides of opioid treatment for chronic, non-cancer pain are becoming increasingly evident. Despite these data, current clinical practice frequently initiates and continues opioid prescriptions for patients with neuropathic pain before prescribing guideline-recommended treatments.

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The Emerging Role of Mechanosensitive Piezo Channels in Migraine Pain.

Recently discovered mechanosensitive Piezo channels emerged as the main molecular detectors of mechanical forces. The functions of Piezo channels range from detection of touch and pain, to control of the plastic changes in different organs. Recent studies suggested the role of Piezo channels in migraine pain, which is supposed to originate from the trigeminovascular nociceptive system in meninges. Interestingly, migraine pain is associated with such phenomenon as mechanical hypersensitivity, suggesting enhanced mechanotransduction. In the current review, we present the data that propose the implication of Piezo channels in migraine pain, which has a distinctive pulsatile character. These data include: (i) distribution of Piezo channels in the key elements of the trigeminovascular nociceptive system; (ii) the prolonged functional activity of Piezo channels in meningeal afferents providing a mechanistical basis for mechanotransduction in nociceptive nerve terminals; (iii) potential activation of Piezo channels by shear stress and pulsating blood flow; and (iv) modulation of these channels by emerging chemical agonists and modulators, including pro-nociceptive compounds. Achievements in this quickly expanding field should open a new road for efficient control of Piezo-related diseases including migraine and chronic pain.

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Factors Associated with Sleep Quality in Patients with Chronic Widespread Pain Attending Multidisciplinary Treatment.

(i) To investigate the prevalence of poor sleep quality and (ii) to explore the associations between clinical, cognitive and emotional factors and quality of sleep in patients with chronic widespread pain (CWP) attending multidisciplinary treatment.

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Commentary on Hayes et al. (2019): The harms of opioid dose escalation in the management of chronic non-cancer pain.

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No benefit from amitriptyline for chronic low back pain?

DTB commentaries provide an overview of, and commentary on, a clinical trial, systematic review or observational study.

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A cross-sectional survey of the perspectives of older people in the Scottish Highlands on the management of their chronic pain.

Although there is evidence of suboptimal outcomes in older people with chronic pain, little emphasis has been placed on those in remote and rural settings.

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Contact Heat Evoked Potentials Are Responsive to Peripheral Sensitization: Requisite Stimulation Parameters.

The sensitizing effect of capsaicin has been previously characterized using laser and contact heat evoked potentials (LEPs and CHEPs) by stimulating in the primary area of hyperalgesia. Interestingly, only CHEPs reveal changes consistent with notion of peripheral sensitization (i.e., reduced latencies). The aim of this study was to investigate contact heat stimulation parameters necessary to detect peripheral sensitization related to the topical application of capsaicin, and therefore significantly improve the current method of measuring peripheral sensitization via CHEPs. Rapid contact heat stimulation (70°C/s) was applied from three different baseline temperatures (35, 38.5, and 42°C) to a 52°C peak temperature, before and after the topical application of capsaicin on the hand dorsum. Increased pain ratings in the primary area of hyperalgesia were accompanied by reduced N2 latency. Changes in N2 latency were, however, only significant following stimulation from 35 and 38.5°C baseline temperatures. These findings suggest that earlier recruitment of capsaicin-sensitized afferents occurs between 35 and 42°C, as stimulations from 42°C baseline were unchanged by capsaicin. This is in line with reduced thresholds of type II A-delta mechanoheat (AMH) nociceptors following sensitization. Conventional CHEP stimulation, with a baseline temperature below 42°C, is well suited to objectively detect evidence of peripheral sensitization.

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Sleep and Pain in Subjects with Fibromyalgia and Comorbid Insomnia: Double-blind, Crossover, Study of Suvorexant 20 mg versus Placebo.

The chronic pain disorder, fibromyalgia, is associated with sleep disturbance, typically sleep maintenance. No studies have evaluated the effect of sleep medication on pain sensitivity in this population. Suvorexant, an orexin antagonist, approved for treatment of insomnia was evaluated for effects on both the sleep and pain of fibromyalgia.

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Multicentre, double-blind, randomised, sham-controlled trial of 10 khz high-frequency spinal cord stimulation for chronic neuropathic low back pain (MODULATE-LBP): a trial protocol.

Chronic neuropathic low back pain (CNLBP) is a debilitating condition in which established medical treatments seldom alleviate symptoms. Evidence demonstrates that high-frequency 10 kHz spinal cord stimulation (SCS) reduces pain and improves health-related quality of life in patients with failed back surgery syndrome (FBSS), but evidence of this effect is limited in individuals with CNLBP who have not had surgery. The aim of this multicentre randomised trial is to assess the clinical and cost-effectiveness of 10 kHz SCS for this population.

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Time-course of Pain Threshold after Continuous Theta Burst Stimulation of Primary Somatosensory Cortex in Pain-free Subjects.

Primary somatosensory cortex (S1) is involved in pain processing and thus its suppression using neuromodulatory techniques such as continuous theta burst stimulation (cTBS) might be a potential pain management strategy in patients with neuropathic pain. cTBS over S1 is known to elevate pain threshold in young adults. However, the time course of this after-effect is unknown. Furthermore, the effect of cTBS over S1 on pain threshold might be confounded by changes in the excitability of primary motor cortex (M1), an area known to be involved in pain processing, due to spread of current. Therefore, whether S1 plays a role in pain processing independent of M1 also remains unknown. The corticospinal excitability (CSE) can provide a measure of M1 excitability because cTBS over M1 is known to reduce CSE. Here, we studied the time-course of the effects of MRI-guided cTBS over S1 on electrical pain threshold and CSE. Ten healthy young adults received cTBS over S1 and sham stimulation in counterbalanced sessions at least 5 days apart. Electrical pain threshold (EPT) and CSE were recorded before and following cTBS over S1. We assessed each measure once before stimulation and then every 10 min starting immediately after stimulation until 40 min. cTBS over S1 elevated EPT compared to sham stimulation with the after-effect lasting for 40 min. We observed no change in CSE following cTBS and sham stimulation. Our findings suggest that cTBS over S1 can elevate EPT for 40 minutes without altering M1 excitability.

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Differential Regulation of the Glucocorticoid Receptor in a Rat Model of Inflammatory Pain.

Anti-inflammatory corticosteroids are a common treatment for different conditions involving chronic pain and inflammation. Clinically used steroids target the glucocorticoid receptor (GR) for its anti-inflammatory effects. We previously reported that GR in sensory neurons may play central roles in some pain models and that GR immunoreactivity signal in dorsal root ganglia (DRG) decreased after local inflammation of the DRG (a model of low back pain). In the current study, we aimed to determine if similar changes in GR signal also exist in a skin inflammation model, the complete Freund's adjuvant (CFA) model (a model of peripheral inflammatory pain), in which the terminals of the sensory neurons rather than the somata are inflamed.

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Association between Inflammatory Biomarkers and Non-specific Low Back Pain: A Systematic Review.

Chronic inflammation increases the production of cytokines and activates pro-inflammatory pathways which may lead to non-specific low back pain (LBP). We systematically reviewed the literature to investigate whether inflammatory biomarkers are associated with non-specific LBP.

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Integrating Motivational Interviewing in Pain Neuroscience Education for People With Chronic Pain: A Practical Guide for Clinicians.

Pain neuroscience education (PNE) and motivational interviewing (MI) have been widely implemented and tested in the field of chronic pain management, and both strategies have been shown to be effective in the short term (small effect sizes) for the management of chronic pain. PNE uses contemporary pain science to educate patients about the biopsychosocial nature of the chronicity of their pain experience. The goal of PNE is to optimize patients' pain beliefs/perceptions to facilitate the acquisition of adaptive pain coping strategies. MI, on the other hand, is a patient-centered communication style for eliciting and enhancing motivation for behavior change by shifting the patient away from a state of indecision or uncertainty. Conceptually, PNE and MI appear to be complementary interventions, with complementary rather than overlapping effects; MI primarily improves cognitive and behavioral awareness and, potentially, adherence to treatment principles, whereas PNE potentially increases pain knowledge/beliefs, awareness, and willingness to explore psychological factors that are potentially associated with pain. Therefore, combining PNE with MI might lead to improved outcomes with larger and longer-lasting effect sizes. The combined use of PNE and MI in patients having chronic pain is introduced here, along with a description of how clinicians might be able to integrate PNE and MI in the treatment of patients experiencing chronic pain. Clinical trials are needed to examine whether combining PNE with MI is superior to PNE or MI alone for improving pain and quality of life in patients having chronic pain.

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Adverse Childhood Experiences Increase Risk for Prescription Opioid Misuse.

The United States is in the midst of an opioid overdose epidemic, with a significant portion of the burden associated with prescription opioids. In response, the CDC released a Guideline for Prescribing Opioids for Chronic Pain, which promotes access to treatment for opioid use disorder. Decades of research have linked childhood adversity to negative health and risk behavior outcomes, including substance misuse. Our present study builds upon this work to examine the relationship between adverse childhood experiences (ACEs) and prescription opioid misuse. We compiled data from the Behavioral Risk Factor Surveillance System implemented by Montana and Florida in 2010 and 2011, respectively. Logistic regressions (run in 2017) tested the associations between ACEs and subsequent prescription pain medicine/opioid misuse outcomes in adulthood. ACEs were prevalent, with 62.7% of respondents in Montana and 50% in Florida reporting at least one ACE. The presence of ACEs was positively associated with prescription opioid misuse across both samples. Respondents reporting three or more ACEs had increased odds of taking opioids more than prescribed, without a prescription, and for the feeling they cause. Our results support a strong link between ACEs and prescription opioid misuse. Opportunities to prevent opioid misuse start with assuring safe, stable, nurturing relationships and environments in childhood and across the lifespan to prevent ACEs from occurring, and intervening appropriately when they do occur. Substance use prevention programs for adolescents, appropriate pain management and opioid prescribing protocols, and treatments for opioid use disorder can address ACEs by enhancing treatment safety and effectiveness and can reduce the intergenerational continuity of early adversity.

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Pellino1 Contributes to Morphine Tolerance by Microglia Activation via MAPK Signaling in the Spinal Cord of Mice.

Chronic morphine-induced antinociceptive tolerance is a major unresolved issue in clinical practices, which is associated with microglia activation in the spinal cord. E3 ubiquitin ligase Pellino1 (Peli1) is known to be an important microglia-specific regulator. However, it is unclear whether Peli1 is involved in morphine tolerance. Here, we found that Peli1 levels in the spinal cord were significantly elevated in morphine tolerance mouse model. Notably, Peli1 was expressed in a great majority of microglia in the spinal dorsal horn, while downregulation of spinal Peli1 attenuated the development of morphine tolerance and associated hyperalgesia. Our biochemical data revealed that morphine tolerance-induced increase in Peli1 was accompanied by spinal microglia activation, activation of mitogen-activated protein kinase (MAPK) signaling, and production of proinflammatory cytokines. Peli1 additionally was found to promote K63-linked ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) in the spinal cord after repeated morphine treatment. Furthermore, knocking down Peli1 in cultured BV2 microglial cells significantly attenuated inflammatory reactions in response to morphine challenge. Therefore, we conclude that the upregulation of Peli1 in the spinal cord plays a curial role in the development of morphine tolerance via Peli1-dependent mobilization of spinal microglia, activation of MAPK signaling, and production of proinflammatory cytokines. Modulation of Peli1 may be a potential strategy for the prevention of morphine tolerance.

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Downregulation of spinal angiotensin converting enzyme 2 is involved in neuropathic pain associated with type 2 diabetes mellitus in mice.

We have previously reported that the spinal angiotensin (Ang) system is involved in the modulation of streptozotocin (STZ)-induced diabetic neuropathic pain in mice. An important drawback of this model however is the fact that the neuropathic pain is independent of hyperglycemia and produced by the direct stimulation of peripheral nerves. Here, using the leptin deficient ob/ob mouse as a type 2 diabetic model, we examined whether the spinal Ang system was involved in naturally occuring diabetic neuropathic pain. Blood glucose levels were increased in ob/ob mice at 5-15 weeks of age. Following the hyperglycemia, persistent tactile and thermal hyperalgesia were observed at 11-14 and 9-15 weeks of age, respectively, which was ameliorated by insulin treatment. At 12 weeks of age, the expression of Ang-converting enzyme (ACE) 2 in the spinal plasma membrane fraction was decreased in ob/ob mice. Spinal ACE2 was expressed in neurons and microglia but the number of NeuN-positive neurons was decreased in ob/ob mice. In addition, the intrathecal administration of Ang (1-7) and SB203580, a p38 MAPK inhibitor, attenuated hyperalgesia in ob/ob mice. The phosphorylation of spinal p38 MAPK was also attenuated by Ang (1-7) in ob/ob mice. These inhibitory effects of Ang (1-7) were prevented by A779, a Mas receptor antagonist. In conclusion, we revealed that the Ang (1-7)-generating system is downregulated in ob/ob mice and is accompanied by a loss of ACE2-positive neurons. Furthermore, Ang (1-7) decreased the diabetic neuropathic pain through inhibition of p38 MAPK phosphorylation via spinal Mas receptors.

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Long-term outcomes of multimodal rehabilitation in primary care for patients with chronic pain.

To investigate the outcomes 1 year after multimodal rehabilitation programmes in primary care for patients with chronic pain, both as a whole and for men and women separately. A second aim was to identify predictive factors for not being on sickness absence at follow-up after 1 year.

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Retrospective Chart Review of Intravenous Valproate Sodium as a Preventive Treatment for Patients With Chronic Migraine.

This is a small pilot study to evaluate the effectiveness of an intravenous (IV) valproate sodium therapy protocol for migraine prevention in a population of patients with chronic migraine refractory to multiple preventive medications.

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Tapentadol prolonged release for managing moderate to severe chronic neck pain with or without a neuropathic component.

Despite the high prevalence of neck pain, few studies have addressed the pharmacological treatment of this condition. We evaluated the effectiveness of tapentadol prolonged-release (PR) in patients with or without a neuropathic pain component, with a focus on functional movements, disability and Quality of Life (QoL). Observational, retrospective study. Ninety-four adult patients with severe neck pain not responsive to opioid step III treatment. The primary endpoint was a ≥30% improvement of pain intensity at 4 weeks (W4). Several secondary outcomes were evaluated, including neck disability index (NDI), range of motion (ROM), and QoL. Patients received tapentadol PR at the starting dose of 100 mg/day. Dose titration was allowed in 50 mg increments, up to 500 mg daily. At W4, the primary endpoint of ≥30% improvement of pain was reported in 70% (n = 35; 95% confidence interval [CI]: 55-82%) of patients with a neuropathic pain component and in 69% (n = 20; 95% CI: 49-85%) of those without a neuropathic component. The percentage of patients reporting a neuropathic pain component significantly decreased from baseline (64.2%) to W4 (27.8%). NDI significantly improved in both groups at W12. ROM significantly improved in all three planes of motion (P < 0.01), with no difference between the two groups. Interference of pain with sleep and QoL also improved. The reduction in pain provided by tapentadol is associated with functional recovery, which may in turn be linked to an improvement in QoL.

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Design and synthesis of N‑(benzylpiperidinyl)‑4‑fluorobenzamide: A haloperidol analog that reduces neuropathic nociception via σ receptor antagonism.

Haloperidol is a neuroleptic drug with high affinity towards the σ receptor (σR), acting as antagonist that decreases neuropathic pain, but has CNS side effects. This work describes the design and synthesis of a novel analog N‑(1‑benzylpiperidin‑4-yl)‑4‑fluorobenzamide (LMH-2), which produced antihyperalgesic and antiallodynic effects in rats with neuropathy induced by chronic constriction injury of the sciatic nerve (CCI), being more active than gabapentin (The most widely used drug for the treatment of neuropathic pain).

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The Role of Cannabidiol (CBD) in Chronic Pain Management: An Assessment of Current Evidence.

Given the growing challenges in chronic pain management coupled with the ongoing consequences of the opioid epidemic, pain management practitioners are looking into more effective, innovative, and safer alternatives to treat pain. Cannabis-based medicine had been described for hundreds of years but only recently have we seen the more scientific, evidence-based approach to its use, and ongoing investigations continue to explore its potential medical benefits. While historically more attention has been paid to the psychoactive component of the cannabis plant Δ-tetrahydrocannabinol (THC), there have been fewer scientific studies on the medical use of the cannabidiol (CBD) – a non-psychoactive component of the cannabis plant.

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Transition from Acute to Chronic Pain in Lower Extremity Fracture Patients: A Pain Phenotyping Protocol.

Traumatic injury is a major source of chronic pain, particularly for individuals with traumatic fracture of the fibula and/or tibia (lower extremity fracture) [LEFx]. Although several factors (e.g., older age, being female sex, high pain intensity at time of initial injury) have been identified as risk factors for chronic pain associated with LEFx. Comprehensive biopsychosical models to predict the odds of transitioning from acute to chronic pain after LEFx are needed to better understand the underlying processes, predict risk for chronic pain, and develop personalized therapies for individuals at higher risk for developing chronic pain.

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Responses after spinal interventions in a clinical pain practice – a pragmatic observational study.

Introduction There is limited evidence for effect of interventional treatment, and pragmatic studies are needed to assess these interventions within a clinical setting. The aim of this study was to describe patients referred to an interventional pain clinic and investigate responses after spinal intervention in general and for radiofrequency ablation (RFA) and transforaminal epidural corticosteroid administration (TECA), specifically. Methods This is a prospective, non-controlled study of patients with chronic spinal pain. The procedures were performed in accordance with the Spine Intervention Society recommendations. Outcome data after a median of 4.5 months are presented, and for those treated with RFA also after 6 and 12 months. Results Among 815 patients, 190 patients underwent diagnostic blocks only and 625 interventional treatment, of these 94 RFA and 246 TECA. Of the whole sample 70% reported pain reduction, for 49% ≥ 50%, while 9% were pain free (p < 0.001). Highest pain intensity decreased from 7.1 to 5.4 [95% Confidence Interval of the Difference (95%-CI): 1.4-1.9] (p < 0.001), while Euroqual – visual analogue scale for general health (EQ-VAS) improved from 48 to 58 (95%-CI: 7.6-11.9) (p < 0.001), and Euroqual-5 Dimensions-5 Levels Index for health related quality of life (EQ-5D-5L Index) from 0.489 to 0.628 (95%-CI: 0.123-0.157) (p < 0.001). The proportions, not taking analgesics, increased from 16% to 30%, and proportion taking strong opioids decreased from 14% to 9% (p < 0.001). We found no significant change in proportion receiving physiotherapy/other treatment nor occupational status. No complications were reported. Among patients treated with RFA, 77% reported pain reduction, for 56% ≥ 50%, while 9% were pain free (p < 0.001). Highest pain intensity decreased from 6.9 to 4.6 (95%-CI: 1.6-3.0) (p < 0.001), while EQ-VAS improved from 47 to 57 (95%-CI: 4.8-13.6 (p < 0.001), and EQ-5D-5L Index from 0.489 to 0.643 (95%-CI: 0.117-0.191) (p < 0.001). The proportion not taking analgesics, increased from 7% to 23% and proportion taking strong opioids decreased from 16% to 10%. Among patients who responded at 6- and 12-month follow up, the proportions reporting pain reduction, EQ-VAS, and EQ-5D-5L Index remained significantly improved from baseline, and the change in proportions taking analgesic and opioids achieved statistical significance. We found no significant change in proportion receiving physiotherapy/other treatment nor occupational status. Among patients treated with TECA, 58% reported pain reduction, for 36% ≥ 50%, while 5% were pain free (p < 0.001). Highest pain intensity decreased from 7.2 to 6.2 (95%-CI 0.5-1.4) (p < 0.001), while EQ-VAS improved from 46 to 52 (95%-CI: 2.0-3.6) (p < 0.001), and EQ-5D-5L Index from 0.456 to 0.571 (95%-CI: 0.077-0.138) (p < 0.001). The proportions, not taking analgesics, increased from 17% to 27% and proportion taking strong opioids decreased from 15% to 10%, but the changes did not reach statistical significance. We found no significant changes in the proportion who recieved physiotherapy/other treatment nor occupational status. Conclusion The study demonstrates substantial short-term responses after spinal intervention and long-lasting improvement for a subsample of the RFA treated patients. We observed larger proportions reporting pain reduction among those treated with cervical RFA. Implementation Quality assessment should be implemented in interventional pain clinics to improve treatment quality.

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Efficacy of pregabalin for the treatment of chronic pruritus of unknown origin, assessed based on electric current perception threshold.

Chronic pruritus of unknown origin (CPUO) is defined as itching lasting more than 6 weeks in the absence of discernible skin lesions. Pregabalin is used to treat patients with CPUO. In this study, we aimed to investigate differences in the perception threshold of itch sensation between patients with CPUO and healthy individuals and to evaluate the efficacy of pregabalin for CPUO. At baseline, week 2, and week 4 after treatment initiation, the visual analogue scale (VAS) score was measured to assess pruritus severity, and electric current perception threshold (CPT) was measured at 250 and 5 Hz using a NEUROMETER CPT/C stimulator. Twenty healthy individuals and 41 patients with CPUO were enrolled in this study. The patients with CPUO were categorised as those who responded to antihistamines (Antihistamine group), were not improved by antihistamines (Pregabalin group), and were not improved by antihistamines and pregabalin (Refractory group). The baseline CPT values were not significantly different between patients with CPUO and healthy control. Pruritus was improved in 7 of 10 patients in the Pregabalin group after treatment with pregabalin, showing decreased CPT at 5 Hz. The sensitive C-fibres presented a high threshold to detect itch sensation, and this sensitivity decreased in response to treatment with pregabalin.

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Pharmacological evaluation of a novel corticotrophin-releasing factor 1 receptor antagonist T-3047928 in stress-induced animal models in a comparison with alosetron.

The major symptoms of irritable bowel syndrome (IBS) are changes in bowel habits and abdominal pain. Psychological stress is the major pathophysiological components of IBS. Corticotropin-releasing factor (CRF) is a well-known integrator in response to psychological stress. In this study, a novel CRF1 receptor antagonist T-3047928 was evaluated in stress-induced IBS models of rats to explore its potency for IBS.

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Effects of oxycodone and diazepam alone and in combination on operant nociception.

Developing effective analgesics with fewer unwanted side effects is a pressing concern. Due to a lack of effective nonopioid options currently available, an alternative approach termed opioid-sparing evaluates the ability of a coadministered drug to reduce the amount of opioid needed to produce an antinociceptive effect. Opioids and benzodiazepines are often coprescribed. Although this approach is theoretically rational given the prevalent comorbidity of chronic pain and anxiety, it also has inherent risks of respiratory depression, which is likely responsible for the substantial percentage of fatal opioid overdoses that have involved benzodiazepines. Moreover, there have been no clinical trials to support the effectiveness of this drug combination nor has there been corroborative preclinical evidence using traditional animal models of nociception. The present studies examined the prescription µ-opioid analgesic oxycodone (0.003-0.1 mg/kg) and the prototypical benzodiazepine anxiolytic diazepam (0.03-1.0 mg/kg), alone and in combination, using an animal model of pain that examines the restoration of conflict-related operant behavior as evidence of analgesia. Results documented significant dose-related increases in thermal threshold following oxycodone treatment. Diazepam treatment alone did not produce significant antinociception. In combination, diazepam pretreatment shifted oxycodone functions upward in a dose-dependent manner, but the additive effects were limited to a narrow dose range. In addition, combinations of diazepam and oxycodone at higher doses abolished responding. Taken together, though intriguing, these findings do not provide sufficient evidence that coadministration of an anxiolytic will result in clinically relevant opioid-sparing for pain management, especially when considering the inherent risks of this drug class combination.

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Allosteric Cannabinoid Receptor 1 (CB1) Ligands Reduce Ocular Pain and Inflammation.

Cannabinoid receptor 1 (CB1) activation has been reported to reduce transient receptor potential cation channel subfamily V member 1 (TRPV1)-induced inflammatory responses and is anti-nociceptive and anti-inflammatory in corneal injury. We examined whether allosteric ligands, can modulate CB1 signaling to reduce pain and inflammation in corneal hyperalgesia. Corneal hyperalgesia was generated by chemical cauterization of cornea in wildtype and CB2 knockout (CB2) mice. The novel racemic CB1 allosteric ligand GAT211 and its enantiomers GAT228 and GAT229 were examined alone or in combination with the orthosteric CB1 agonist Δ-tetrahydrocannabinol (Δ-THC). Pain responses were assessed following capsaicin (1 µM) stimulation of injured corneas at 6 h post-cauterization. Corneal neutrophil infiltration was also analyzed. GAT228, but not GAT229 or GAT211, reduced pain scores in response to capsaicin stimulation. Combination treatments of 0.5% GAT229 or 1% GAT211 with subthreshold Δ-THC (0.4%) significantly reduced pain scores following capsaicin stimulation. The anti-nociceptive effects of both GAT229 and GAT228 were blocked with CB1 antagonist AM251, but remained unaffected in CB2 mice. Two percent GAT228, or the combination of 0.2% Δ-THC with 0.5% GAT229 also significantly reduced corneal inflammation. CB1 allosteric ligands could offer a novel approach for treating corneal pain and inflammation.

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