Articles: hyperalgesia.
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Pharmacol. Biochem. Behav. · Jul 2015
Intrathecal injection of KN93 attenuates paradoxical remifentanil-induced postoperative hyperalgesia by inhibiting spinal CaMKII phosphorylation in rats.
Remifentanil is a short-acting and highly selective mu opiate agonist that is used in many clinical surgical situations for intraoperative pain relief. Under certain conditions, remifentanil can produce "paradoxical" hyperalgesia. This study aims to investigate mechanisms of actions mediating this "paradoxical" effect. ⋯ Intrathecal injection of KN93 attenuates postoperative hyperalgesia induced by intraoperative infusion of remifentanil in rats through inhibiting spinal CaMKII phosphorylation.
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Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie, conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed to modulate pain, the mechanisms underlying analgesia remain poorly understood. To further elucidate how TENS modulates pain, we examined evoked responses to noxious thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers. We hypothesized that sensitization caused by capsaicin application would unmask TENS analgesia, which could not be detected in the absence of sensitization. Forty-nine healthy subjects took part in a series of experiments. The experiments comprised the application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder), and assessing rating of perception (numeric rating scale: 0-10) and evoked potentials to noxious contact heat stimuli. The extrasegmental site was included as a control condition because previous studies indicate no analgesic effect to remote conventional TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials in subjects untreated with capsaicin. However, segmental TENS applied in conjunction with capsaicin significantly reduced sensation to noxious thermal stimuli following a 60-minute period of sensitization. ⋯ The study indicates that sensitization with capsaicin unmasks the analgesic effect of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate that TENS may be interacting segmentally to modulate distinct aspects of sensitization, which in turn results in analgesia to thermal stimulation.
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Observational Study
Influence of Centrally Mediated Symptoms on Postoperative Pain in Osteoarthritis Patients Undergoing Total Knee Arthroplasty: A Prospective Observational Evaluation.
Central sensitization plays an important role in the chronic pain experienced by osteoarthritis (OA) patients. In this prospective observational study, we investigated the influence of the level of preoperative centrally mediated symptoms measured by the Central Sensitization Inventory (CSI) on pain intensity after total knee arthroplasty (TKA) for OA. ⋯ OA patients with high levels of comorbid centrally mediated symptoms showed severe pain and increased analgesic requirements after TKA in the early postoperative period. Moreover, these patients seemed to be at higher risk of persistent pain, and a high CSI score was predictive of low patient satisfaction in terms of pain relief after surgery.
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Clin. Exp. Pharmacol. Physiol. · Jul 2015
Inhibition of microglial activity alters spinal wide dynamic range neuron discharge and reduces microglial Toll-like receptor 4 expression in neuropathic rats.
It is believed that neuropathic pain results from aberrant neuronal discharges although some evidence suggests that the activation of glia cells contributes to pain after an injury to the nervous system. This study aimed to evaluate the role of microglial activation on the hyper-responsiveness of wide dynamic range neurons (WDR) and Toll-like receptor 4 (TLR4) expressions in a chronic constriction injury (CCI) model of neuropathic pain in rats. Adult male Wistar rats (230 ± 30 g) underwent surgery for induction of CCI neuropathy. ⋯ Post-injury administration of minocycline effectively decreased thermal hyperalgesia, TLR4 expression, and hyper-responsiveness of WDR neurons in CCI rats. The results of this study indicate that post-injury, repeated administration of minocycline attenuated neuropathic pain by suppressing microglia activation and reducing WDR neuron hyper-responsiveness. This study confirms that post-injury modulation of microglial activity is a new strategy for treating neuropathic pain.
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Cast immobilization induces mechanical hypersensitivity, which disturbs rehabilitation. Although vibration therapy can reduce various types of pain, whether vibration reduces immobilization-induced hypersensitivity remains unclear. ⋯ The data suggest that initiation of vibration therapy in the early phase of immobilization may inhibit the development of immobilization-induced hypersensitivity.