Articles: hyperalgesia.
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Interleukin-6 (IL-6) is an inflammatory cytokine known to modulate muscle pain. However, the mechanisms underlying this effect still remain unclear. Here we show that the injection of IL-6 into mice gastrocnemius muscle evoked a time- and dose-dependent mechanical hyperalgesia. ⋯ Simultaneous flow cytometry measurements revealed that ERK, p38 MAPK and JNK were phosphorylated as early as 5 min after IL-6 injection. These findings provided new evidence indicating that IL-6 exerts a relevant role in the development and maintenance of muscular hyperalgesia. The IL-6-mediated muscular pain response involves resident cell activation, polymorphonuclear cell infiltration, cytokine production, prostanoids and sympathomimetic amines release and the activation of intracellular pathways, especially MAPKs.
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The Journal of physiology · Nov 2010
Magnesium attenuates chronic hypersensitivity and spinal cord NMDA receptor phosphorylation in a rat model of diabetic neuropathic pain.
Neuropathic pain is a common diabetic complication affecting 8-16% of diabetic patients. It is characterized by aberrant symptoms of spontaneous and stimulus-evoked pain including hyperalgesia and allodynia. Magnesium (Mg) deficiency has been proposed as a factor in the pathogenesis of diabetes-related complications, including neuropathy. ⋯ Magnesium supplementation failed to reduce hyperglycaemia, polyphagia and hypermagnesiuria, or to restore intracellular Mg levels and body growth, but increased insulinaemia and reduced polydipsia. Moreover, it abolished thermal and tactile allodynia, delayed the development of mechanical hypersensitivity, and prevented the increase in spinal cord dorsal horn pNR1. Thus, neuropathic pain symptoms can be attenuated by targeting the Mg-mediated blockade of NMDA receptors, offering new therapeutic opportunities for the management of chronic neuropathic pain.
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The Journal of physiology · Nov 2010
Endogenous descending modulation: spatiotemporal effect of dynamic imbalance between descending facilitation and inhibition of nociception.
In conscious rats, we investigated the change of nociceptive paw withdrawal reflexes elicited by mechanical and heat stimuli during intramuscular (i.m.) 5.8% hypertonic (HT) saline elicited muscle nociception. i.m. injection of HT saline caused rapid onset, long lasting (around 7 days), bilateral mechanical hyperalgesia, while it induced bilateral, slower onset (1 day after the HT saline injection), long-term (about 1-2 weeks) heat hypoalgesia. Ipsilateral topical pre-treatment of the sciatic nerve with 1% capsaicin significantly prevented the occurrence of both the bilateral mechanical hyperalgesia and the contralateral heat hypoalgesia. Intrathecal administration of either 6-hydroxydopamine hydrobromide (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT), and intraperitoneal injection of naloxone all markedly attenuated the HT saline induced bilateral heat hypoalgesia, but not the mechanical hyperalgesia. ⋯ However, this discriminative function is physiologically silent or inactive, and can be triggered by stimulation of peripheral C-fibre afferents. Importantly, in contrast to the rapid onset of descending facilitation, the late occurrence of descending inhibition suggests a requirement of continuous C-fibre input and temporal summation. Thus, a reduction of C-fibre input using exogenous analgesic agents, i.e. opioids, may counteract the endogenous descending inhibition.
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Painful neuropathy is a common complication of diabetes. Particularly in the early stage of diabetic neuropathy, patients are characterized by burning feet, hyperalgesia to heat, and mechanical stimuli, as if residual nociceptors were sensitized. Such symptoms are barely explained by common pathophysiological concepts of diabetic neuropathy. ⋯ Diabetic C-fibers show exaggerated sensitivity to hyperglycemic hypoxia with and without additional acidosis, conditions that are thought to mimic ischemic episodes in diabetic nerves. Ongoing C-fiber discharge is known to induce spinal sensitization. Together with altered receptor and ion channel expressions this may contribute to painful episodes in diabetic neuropathy.
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Opioids are the most potent drugs for treatment of acute and chronic pain. However, accumulating evidence suggests that opioids may paradoxically also enhance pain, often referred to as opioid-induced hyperalgesia. Opioid-induced hyperalgesia is defined as an increased sensitivity to pain or a decreased pain threshold in response to opioid therapy. ⋯ However, it remains unclear whether opioid-induced hyperalgesia develops during continuous chronic application of opioids or on their withdrawal. This review provides a comprehensive summary of clinical research concerning opioid-induced hyperalgesia and the molecular mechanisms of opioid withdrawal and opioid tolerance and other potential mechanisms which might induce hyperalgesia during opioid therapy will be discussed. The status quo of our knowledge will be summarized and the clinical relevance of opioid-induced hyperalgesia will be discussed.