Pain
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Fibromyalgia is a prevalent and burdensome disorder characterized by chronic widespread pain and complex comorbid symptoms. To develop better treatments for pain-centered fibromyalgia symptoms, there is still a need for animal models which mimic the features of fibromyalgia patients. In the present study, we have established a fibromyalgia animal model by utilizing a never-before-published pharmacological effect of reserpine. ⋯ Pregabalin, duloxetine, and pramipexole significantly attenuated the reserpine-induced decrease in muscle pressure threshold, but diclofenac did not. The validity of the use of this reserpinized animal as a fibromyalgia model is demonstrated from three different aspects, i.e., face validity (manifestation of chronic pain and comorbid symptoms), construct validity (dysfunction of biogenic amine-mediated central nervous system pain control is involved), and predictive validity (similar responses to treatments used in fibromyalgia patients). This animal model is expected to contribute to the better understanding of fibromyalgia pathophysiology and the evaluation of drugs, especially those which would activate biogenic amine system.
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Randomized Controlled Trial
Reduction of allodynia in patients with complex regional pain syndrome: A double-blind placebo-controlled trial of topical ketamine.
A double-blind placebo-controlled crossover trial was used to determine the effects of topical ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, on the sensory disturbances in 20 patients with complex regional pain syndrome (CRPS). On two occasions separated by at least one week, sensory tests to light touch, pressure, punctate stimulation, light brushing and thermal stimuli were performed in the symptomatic and contralateral limb and on each side of the forehead before and 30min after 10% ketamine cream was applied to the symptomatic or healthy limb. Venous blood for the plasma estimations of ketamine and norketamine was obtained 1h after application of the creams. ⋯ Allodynia and hyperalgesia were detected in the ipsilateral forehead to a range of stimuli (brushing, pressure, punctate stimulation, cold, heat, and warmth). In several patients, ketamine treatment of the symptomatic limb inhibited allodynia to brushing the ipsilateral forehead, suggesting that the mechanism that mediates allodynia in the symptomatic limb contributed to allodynia at more remote sites. The present study shows promise for the use of topical ketamine as opposed to parenteral and oral forms which often result in undesirable side effects.
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Randomized Controlled Trial
Intrathecal glycine for pain and dystonia in complex regional pain syndrome.
Since glycinergic neurotransmission plays an important inhibitory role in the processing of sensory and motor information, intrathecal glycine (ITG) administration may be a potential therapy for both pain and movement disorders in patients with complex regional pain syndrome (CRPS). Aims of the current study, which is the first report on ITG in humans, were to evaluate its safety and efficacy. ITG treatment during 4 weeks was studied in CRPS patients with dystonia in the period before they received intrathecal baclofen treatment. ⋯ Although there was a trend to worsening on the CGI and PGI during ITG treatment, there were no significant differences between ITG and placebo treatment in any of the outcomes. ITG given over 4 weeks was ineffective for pain or dystonia in CRPS. Although no serious adverse events occurred, further studies are required to rule out potential neurotoxicity of ITG.
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Adrenomedullin (AM), a member of calcitonin gene-related peptide (CGRP) family, has been demonstrated to be a pronociceptive mediator [28]. This study was undertaken to investigate the role of AM in a model of complete Freund's adjuvant (CFA)-induced inflammatory pain. Injection of CFA, but not of saline, in the unilateral hindpaw produced an increase in the expression of AM-like immunoreactivity (AM-IR) in laminae I-II of the spinal cord as well as in small- and medium-sized dorsal root ganglion (DRG) neurons at 48 h. ⋯ Furthermore, blockade of AM receptors abolished CFA-induced changes in the expression and content of CGRP-like immunoreactivity in these regions. Taken together, our results suggest that the upregulation of AM in DRG neurons contributes to the development of inflammatory pain, and this effect is mediated, at least in part, by enhancing the expression and release of CGRP. Blocking AM receptor downstream signaling effects using antagonists has the potential of relieving pain following the induction of inflammation.
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Epibatidine has shown antinociceptive effects in various pain models, being 200-fold more potent than morphine. Previous results from our laboratory demonstrated that HO-1 overexpression has an antinociceptive effect in the formalin test. Furthermore, epibatidine was able to induce haeme oxygenase-1 (HO-1). ⋯ Furthermore, the antinociceptive effect of epibatidine was related to the activation of alpha7 and/or alpha9 nAChRs since methyllycaconitine (MLA) and mecamylamine but not dihydro-beta-erythroidine (DHbetaE) reverted this effect. Finally, we showed by flow cytometry and by immunofluorescence that white blood cells of the animals injected with epibatidine expressed more HO-1 than control animals, and this expression was also reverted by MLA pre-treatment. These findings demonstrate that HO-1 induction by epibatidine has antinociceptive and anti-inflammatory effects by the activation of MLA-sensitive nAChRs.