The journal of pain : official journal of the American Pain Society
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Evidence from a number of sources supports the existence of two relatively independent neurophysiological systems that underlie avoidance- and approach-related emotions, cognitions, and behavior. There is considerable overlap between 1) the emotions, cognitions, and behaviors controlled by these two systems, and 2) the known effects of chronic pain. Here we propose a 2-factor model of chronic pain on the basis of these well established 2-factor models, and discuss the implications of the model for understanding the effects of pain and mechanisms of psychological pain treatments. The model makes specific hypotheses, which are unique to the proposed model, regarding the mechanisms underlying pain's negative influence and the benefits of psychological pain treatments. The model also provides an overarching framework that could enhance outcomes by 1) broadening the assessment of factors that may be influencing pain and its effect on individual patients, and 2) suggesting that specific techniques from different treatments may be combined to better target these factors. ⋯ The 2-factor model presented in this report provides a framework for understanding the effects of psychological pain treatments, and makes specific a priori hypotheses regarding the specific mechanisms of those treatments. Clinical applications of the model have the potential for enhancing treatment outcomes.
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Physical exercise can attenuate neuropathic pain (NPP), but the exact mechanism underlying exercise-induced hypoalgesia (EIH) remains unclear. Recent studies have shown that histone hyperacetylation via pharmacological inhibition of histone deacetylases in the spinal cord attenuates NPP, and that histone acetylation may lead to the production of analgesic factors including interleukin 10. We intended to clarify whether histone acetylation in microglia in the spinal dorsal horn contributes to EIH in NPP model mice. C57BL/6J mice underwent partial sciatic nerve ligation (PSL) and PSL- and sham-runner mice ran on a treadmill at a speed of 7 m/min for 60 min/d, 5 days per week, from 2 days after the surgery. PSL-sedentary mice developed mechanical allodynia and heat hyperalgesia, but such behaviors were significantly attenuated in PSL-runner mice. In immunofluorescence analysis, PSL surgery markedly increased the number of histone deacetylase 1-positive/CD11b-positive microglia in the ipsilateral superficial dorsal horn, and they were significantly decreased by treadmill-running. Moreover, the number of microglia with nuclear expression of acetylated H3K9 in the ipsilateral superficial dorsal horn was maintained at low levels in PSL-sedentary mice, but running exercise significantly increased them. Therefore, we conclude that the epigenetic modification that causes hyperacetylation of H3K9 in activated microglia may play a role in producing EIH. ⋯ This article presents the importance of epigenetic modification in microglia in producing EIH. The current research is not only helpful for developing novel nonpharmacological therapy for NPP, but will also enhance our understanding of the mechanisms and availability of exercise in our daily life.
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Review
The Pain Experience of Hispanic Americans: A Critical Literature Review and Conceptual Model.
Although the Hispanic population is a burgeoning ethnic group in the United States, little is known about their pain-related experience. To address this gap, we critically reviewed the existing literature on pain experience and management among Hispanic Americans (HAs). We focused our review on the literature on nonmalignant pain, pain behaviors, and pain treatment seeking among HAs. Pain management experiences were examined from HA patients' and health care providers' perspectives. Our literature search included variations of the term "Hispanic" with "AND pain" in PubMed, Embase, Web of Science, ScienceDirect, and PsycINFO databases. A total of 117 studies met our inclusion criteria. We organized the results into a conceptual model with separate categories for biological and/or psychological and sociocultural and/or systems-level influences on HAs' pain experience, response to pain, and seeking and receiving pain care. We also included information on health care providers' experience of treating HA patients with pain. For each category, we identified future areas of research. We conclude with a discussion of limitations and clinical implications. ⋯ In this critical review of the literature we examined the pain and management experiences of the HA population. We propose a conceptual model, which highlights findings from the existing literature and future areas of research.
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Observational Study
Situational but not dispositional pain catastrophizing correlates with early postoperative pain in pain-free patients before surgery.
Pain catastrophizing may be assessed as a dispositional measure using a previous painful experience as a reference or as a situational measure using an actual ongoing pain as a reference. The latter has shown more robust correlations with pain-related outcomes; the relative influence of dispositional and situational pain catastrophizing remains unknown in relation to populations with no pain before surgery. Forty-two consecutive patients who underwent corrective surgery for funnel chest were asked to complete the Pain Catastrophizing Scale with reference to 1) a previous painful experience (dispositional pain catastrophizing), 2) experimental pain during a 2-minute cold pressor test (situational experimental pain catastrophizing), and 3) clinical pain 3 days after surgery (situational clinical pain catastrophizing) to investigate whether these measures predicted immediate pain intensity and unpleasantness in the early postoperative period. Thirty-four patients were available for analyses. Dispositional pain catastrophizing was unrelated to situational experimental and situational clinical pain catastrophizing and to postoperative pain and unpleasantness (P > .05). In contrast, the 2 situation-specific pain catastrophizing measures were strongly associated (ρ = .59, P = .0002). In analyses adjusted for preoperative anxiety, depression, and cold pressor pain sensitivity, situational experimental and situational clinical pain catastrophizing correlated with postoperative movement-evoked pain (β = 1.36, P = .01 and β = 1.24, P = .02, respectively) and unpleasantness (β = 1.32, P = .01 and β = 1.36, P = .01, respectively). ⋯ Pain catastrophizing should be captured in relation to specific painful events in otherwise healthy patients. Future studies might benefit from assessing situational pain catastrophizing to identify patients at risk for increased postoperative pain to optimize stratified pain treatment.
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Randomized Controlled Trial
High-Definition Transcranial Direct Current Stimulation Enhances Conditioned Pain Modulation in Healthy Volunteers: A Randomised Trial.
Transcranial direct current stimulation (tDCS) is a form of brain stimulation that allows for the selective increase or decrease in the cortical excitability of a targeted region. When applied over the motor cortex it has been shown to induce changes in cortical and subcortical brain regions involved in descending pain inhibition or conditioned pain modulation (CPM). The aim of the current study was to assess whether activation of pain inhibitory pathways via tDCS of the motor cortex facilitates the CPM response. Elevated CPM after active tDCS of the motor cortex was hypothesized. Thirty healthy male volunteers attended 2 experimental sessions separated by 7 days. Both sessions consisted of CPM assessment after 20 minutes of either active or sham (placebo) tDCS over the motor cortex. CPM capacity was assessed via the pain-inhibits-pain protocol; CPM responses were shown to be elevated after active compared with sham tDCS. This report concludes that tDCS of the motor cortex enhances the CPM response in healthy men. This finding supports the potential utility of tDCS interventions in clinical pain treatment. ⋯ The use of noninvasive brain stimulation over the motor cortex was shown to enhance the CPM effect. This finding supports the use of tDCS in the treatment of chronic pain, particularly in sufferers exhibiting maladaptive CPM.