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Altered pro-nociceptive and anti-nociceptive mechanisms are often implicated in painful conditions and have been increasingly studied over the past decade. For some painful conditions alterations are well-established, but in low back pain (LBP) populations there remains considerable debate whether these mechanisms are altered. The present systematic review aimed to address this issue by identifying studies assessing Conditioned Pain Modulation (CPM) and/or Temporal Summation of Pain (TSP) in LBP patients, comparing to either a healthy control group or using a method with reference data available. Qualitative synthesis and quantitative meta-analysis of group differences were performed. For CPM and TSP, 20 and 29 original articles were eligible, with data for meta-analysis obtainable from 18 (1500 patients, 505 controls) and 27 (1507 patients, 1127 controls) studies, respectively. Most studies were of poor-to-fair quality with significant heterogeneity in study size, population, assessment methodology and outcome. Nonetheless, CPM was impaired in LBP patients compared to controls (standardized mean difference = -0.44 [-0.64, -0.23], P<0.001), and the magnitude of this impairment was related to pain chronicity (acute/recurrent versus chronic, P=0.003), duration (R=-0.62, P=0.006) and severity (R=-0.54, P=0.02). TSP was facilitated in LBP patients compared to controls (standardized mean difference = 0.50 [0.29, 0.72], P<0.001), and the magnitude of this facilitation was weakly related to pain severity (R=0.41, P=0.04) and appeared to be influenced by test modality (P<0.001). Impaired CPM and facilitated TSP was present in LBP patients compared to controls, though the magnitude of differences was small which may direct future research on the clinical utility.
Learn More >Exercise is considered an important component of effective chronic pain management and it is well established that long term exercise training provides pain relief. In healthy, pain-free populations, a single bout of aerobic or resistance exercise typically leads to exercise induced hypoalgesia (EIH), a generalized reduction in pain and pain sensitivity that occurs during exercise and for some time afterwards. In contrast, EIH is more variable in chronic pain populations and is more frequently impaired; with pain and pain sensitivity decreasing, remaining unchanged or, in some cases, even increasing in response to exercise. Pain exacerbation with exercise may be a major barrier to adherence, precipitating a cycle of physical inactivity that can lead to long-term worsening of both pain and disability. In order to optimize the therapeutic benefits of exercise, it is important to understand how EIH works, why it may be impaired in some people with chronic pain and how this should be addressed in clinical practice. In this article, we provide an overview of EIH across different chronic pain conditions. We discuss possible biological mechanisms of EIH and the potential influence of sex and psychosocial factors, both in pain-free adults and, where possible, individuals with chronic pain. Clinical implications of impaired EIH are discussed and recommendations are made for future research, including further exploration of individual differences in EIH, the relationship between exercise dose and EIH, the efficacy of combined treatments and the use of alternative measures to quantify EIH. Perspective: This article provides a contemporary review of the acute effects of exercise on pain and pain sensitivity, including in people with chronic pain conditions. Existing findings are critically reviewed, clinical implications are discussed and recommendations are offered for future research.
Learn More >Involvement of Endothelin Receptors in Peripheral Sensory Neuropathy Induced by Oxaliplatin in Mice.
The aim of this study was to evaluate the participation of the endothelin ET and ET receptors and the effects of bosentan in oxaliplatin-induced peripheral sensory neuropathy (OIN) in mice. Adult male Swiss mice received 1 mg/kg of oxaliplatin intravenously, twice a week for 5 weeks. Dorsal root ganglia (DRG) and spinal cords were removed for evaluation of the endothelin ET and ET receptor expression. Afterwards, selective (BQ-123 and BQ-788; 10 nmol in 30 μL, intraplantarly) and non-selective (bosentan, 100 mg/kg, orally) antagonists were administered in order to evaluate the involvement of the endothelin receptors in OIN. Mechanical and thermal nociception tests were performed once a week for 56 days. Oxaliplatin induced mechanical and thermal hypersensitivity and increased the endothelin ET receptor expression in both the DRG and spinal cord (P < 0.05). Endothelin ET receptor expression was increased in the DRG (P < 0.05) but not in the spinal cord. Both endothelin ET and ET receptor selective antagonists partially prevented mechanical hyperalgesia in mice with OIN (P < 0.05). Moreover, bosentan prevented mechanical and thermal hypersensitivity in oxaliplatin-treated mice (P < 0.05). In conclusion, both endothelin ET and ET receptors seem to be involved in the OIN in mice and they should be considered possible targets for the management of this clinical feature.
Learn More >Musculoskeletal pain reduces corticomotor excitability (CE) and methods modulating such CE reduction remain elusive. This study aimed to modulate pain-induced CE reduction by performing action observation and motor imagery (AOMI) during experimental muscle pain. Twelve healthy subjects participated in three cross-over and randomized sessions separated by one week. During the AOMI session subjects performed an AOMI task for 10 mins. In the AOMI+PAIN session, hypertonic saline was injected in the first dorsal interosseous (FDI) muscle prior to performing the AOMI task. In the PAIN session, subjects remained at rest for 10 min or until pain-resolve after the hypertonic saline injection. CE was assessed using transcranial magnetic stimulation motor-evoked potentials (TMS-MEPs) of the FDI muscle at baseline, during, immediately after, and 10 min after AOMI and/or PAIN. Facilitated TMS-MEPs were found after two and four mins of AOMI performance (P<0.017) whereas a reduction in TMS-MEPs appeared at four mins (P<0.017) during the PAIN session. Performing the AOMI task during pain counteracted the reduction in CE, as evident by no change in TMS-MEPs during the AOMI+PAIN session (P>0.017). Pain intensity was similar between the AOMI+PAIN and PAIN sessions (P=0.71). This study, that may be considered a pilot, demonstrated the counteracting effects of AOMI on pain-induced reduction in CE and warrants further studies in a larger population. PERSPECTIVE: This is the first study to demonstrate a method counteracting the reduction in corticomotor excitability associated with acute pain and advances therapeutic possibilities for individuals with chronic musculoskeletal pain.
Learn More >Botulinum toxin A (BTX-A) is a promising therapeutic modality against trigeminal neuralgia (TN) with certain controversies pertaining to its application. To provide further information on factors influencing the treatment outcomes of BTX-A, a retrospective study with 152 patients with TN treated with BTX-A was performed. The starting time and duration of the therapeutic effect, as well as side effects, of BTX-A in the treatment of TN were analyzed by sex, age, course of disease, number of branches and injected dose. A total of 136 patients exhibited symptom improvement within 2 weeks following BTX-A treatment as evaluated using a visual analog scale (VAS). The effect of BTX-A was sustained throughout the initial 6 months of the follow-up and was demonstrated to persist for as long as 28 months. Female sex, short disease course and high injection dose (>70 units) were associated with lower long-term VAS scores. Patients receiving short-term medium-(50-70 units) or high-dose injections were more likely to be completely cured. Patients with a median disease course (1-10 years) or multiple branches were more likely to exhibit facial asymmetry. Based on the stratified analysis, female patients with a median disease course (1-10 years) exhibited a higher incidence of side effects and male patients achieved better treatment outcomes with high BTX-A doses. BTX-A effectively alleviated patients with TN in both short or long term, although the treatment efficacy may depend on patient characteristics.
Learn More >Biobehavioral interventions for migraine incorporate both physiologic and psychological factors. This article details treatments for migraine management and prevention, ranging from traditional to newly emerging interventions. Similarly, this article reviews key person-related factors that may affect migraine prevalence and management. Aspects related to patient-physician relationships and communication are also reviewed. Research involving childhood and adolescent migraine is reviewed, and special considerations regarding this population are summarized. Clinical trials and other studies have provided evidence that these behavioral interventions, when combined with pharmacotherapy, show a marked improvement in primary treatment outcomes, such as a decrease in headache frequency and duration.
Learn More >It is unknown whether clinical parameters differ between migraineurs with and without first-degree family members with migraine.
Learn More >Mu opioid receptor (MOR)-targeting analgesics are efficacious pain treatments, but notorious for their abuse potential. In preclinical animal models, co administration of traditional kappa opioid receptor (KOR)-targeting agonists with MOR-targeting analgesics can decrease reward and potentiate analgesia. However, traditional KOR-targeting agonists are well known for inducing anti-therapeutic side effects (psychotomimesis, depression, anxiety, dysphoria). Recent data suggest that some functionally selective, or biased, KOR-targeting agonists might retain the therapeutic effects of KOR activation without inducing undesirable side effects. Nalfurafine, used safely in Japan since 2009 for uremic pruritus, is one such functionally selective KOR-targeting agonist. Here, we quantify the bias of nalfurafine and several other KOR agonists relative to an unbiased reference standard (U50,488), and show that nalfurafine and EOM-salvinorin-B demonstrate marked G protein-signaling bias. While nalfurafine (0.015 mg/kg) and EOM-salvinorin-B (1 mg/kg) produced spinal anti-nociception equivalent to 5 mg/kg U50,488, only nalfurafine significantly enhanced the supraspinal analgesic effect of 5 mg/kg morphine. In addition, 0.015 mg/kg nalfurafine did not produce significant conditioned place aversion (CPA), yet retained the ability to reduce morphine-induced conditioned place preference (CPP) in C57BL/6J mice. Nalfurafine and EOM-salvinorin-B each produced robust inhibition of both spontaneous and morphine-stimulated locomotor behavior, suggesting a persistence of sedative effects when co-administered with morphine. Taken together, these findings suggest that nalfurafine produces analgesic augmentation, while also reducing opioid-induced reward with less risk of dysphoria. Thus, adjuvant administration of G protein-biased KOR agonists like nalfurafine may be beneficial in enhancing the therapeutic potential of MOR-targeting analgesics, such as morphine. SIGNIFICANCE STATEMENT: N/A.
Learn More >Most canine visits to veterinarians are related to skin diseases with itch being the chief complaint. Historically, several itch-inducing molecules and pathways have been identified in mice, but whether or not these are similar in dogs is not yet known. Herein, we set out to study the expression of pruritogenic neuropeptides, their cognate receptors with a limited functional validation thereof using a multidisciplinary approach. We demonstrated the expression of somatostatin and other major neuropeptides and receptors in canine dorsal root ganglia neurons. Next, we showed that interleukin-31, serotonin, and histamine activate such neurons. Furthermore, we demonstrated the physiological release of somatostatin from dog dorsal root ganglia neurons in response to several endogenous itch mediators. In summary, our results provide the first evidence that dogs use similar pruritogenic pathways to those characterized in mice and we thus identify multiple targets for the future treatment of itch in dogs.
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