Pain
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Regular physical activity in healthy individuals prevents development of chronic musculoskeletal pain; however, the mechanisms underlying this exercise-induced analgesia are not well understood. Interleukin-10 (IL-10), an antiinflammatory cytokine that can reduce nociceptor sensitization, increases during regular physical activity. Since macrophages play a major role in cytokine production and are present in muscle tissue, we propose that physical activity alters macrophage phenotype to increase IL-10 and prevent chronic pain. ⋯ Blockade of IL-10 systemically or locally prevented the analgesia in physically active mice, ie, mice developed hyperalgesia. Conversely, sedentary mice pretreated systemically or locally with IL-10 had reduced hyperalgesia after repeated acid injections. Thus, these results suggest that regular physical activity increases the percentage of regulatory macrophages in muscle and that IL-10 is an essential mediator in the analgesia produced by regular physical activity.
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Number-based assessment tools are used to evaluate pain perception in patients and determine the effect of pain management. The aim of this study was to determine the ability of chronic and acute pain patients to score their response to randomly applied noxious stimuli and assess the effect of opioid treatment. Thirty-seven healthy controls, 30 fibromyalgia patients, and 62 postoperative patients with acute pain received random heat pain (Hp) and electrical pain (Ep) stimuli. ⋯ The data were analyzed using a penalty score system, based on the assumption that stimuli of higher intensity are scored with a greater NRS, and stratified into cohorts corresponding to "good," "mediocre," and "poor" scoring. Healthy controls were well able to score pain with 73% (Hp) and 81% (Ep) of subjects classified into cohort "good." Fibromyalgia had a negative effect on scoring with 45% (Hp, P = 0.03 vs controls) and 67% (Ep) of patients in cohort "good." In controls, scoring deteriorated during opioid administration leaving just 40% (Hp, P = 0.015 vs baseline) and 70% (Ep) of subjects in the cohort "good." Similar observations were made in fibromyalgia patients (P = 0.02) but not in surgical patients with postoperative pain. Consistency to grade pain using an NRS is high in healthy volunteers but deteriorates in chronic pain and during opioid administration to volunteers and chronic pain patients but not to acute pain patients.
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Oscillations are fundamental to communication between neuronal ensembles. We previously reported that pain in awake rats enhances synchrony in primary somatosensory cortex (S1) and attenuates coherence between S1 and ventral posterolateral (VPL) thalamus. Here, we asked whether similar changes occur in anesthetized rats and whether pain modulates phase-amplitude coupling between VPL and S1. ⋯ Systemic or intrathalamic delivery of Z944 to rats with CCI normalized these changes. Systemic Z944 also reversed thermal hyperalgesia and conditioned place preference. These data suggest that pain-induced cortical synchrony and thalamocortical disconnectivity are directly related to burst firing in VPL.