Articles: hyperalgesia.
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Neuropathic pain refers to pain that arises as a direct consequence of a lesion or disease affecting the somatosensory nervous system.(1) Many cases of neuropathic pain run a chronic course, and treatment may be difficult because commonly used analgesics, including NSAIDs and to some extent opioids, are often ineffective. In addition, the use of other pharmacological treatments can be limited by unwanted effects. ⋯ This month and next month we review the drug treatment of neuropathic pain. In this first part we discuss neuropathic pain and the use of antidepressants.
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Review
Cold hyperalgesia as a prognostic factor in whiplash associated disorders: a systematic review.
To review and critically evaluate the existing literature for the prognostic value of cold hyperalgesia in Whiplash Associated Disorders (WAD). ⋯ There is moderate evidence supporting cold hyperalgesia as a prognostic factor for long-term pain and disability outcome in WAD. Further validation of the strength of this relationship and the influence of covariates are required. The mechanism for this relationship is unknown.
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We describe a child with polyarticular juvenile idiopathic arthritis (JIA) presenting with severe diffuse pain refractory to nonsteroidal anti-inflammatory agents and high-dose opioids. Her JIA involved her knees and ankles and was mildly active on etanercept and nonsteroidal anti-inflammatory agents. At presentation, she complained of hip pain progressing to severe diffuse pain and allodynia involving her extremities. ⋯ Despite reports in adults, the phenomenon of OIH has been reported infrequently in children. To our knowledge, OIH has not been described in children with rheumatologic conditions. We recommend investigating the possibility of OIH when treating a child with JIA and severe refractory pain.
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The preprotachykinin A gene (ppt-A) codes for Substance P (SP), supports nociceptive sensitization, and modulates inflammatory responses after incision. Repeated opioid use produces paradoxical pain sensitization-termed opioid-induced hyperalgesia (OIH) -which can exacerbate pain after incision. Here the contribution of SP to peri-incisional nociceptive sensitization and nociceptive mediator production after opioid treatment was examined utilizing ppt-A knockout (-/-) mice and the neurokinin (NK1) receptor antagonist LY303870. Less mechanical allodynia was observed in ppt-A(-/-) mice compared to wild types (wt) after morphine treatment both before and after incision. Moreover, LY303870 administered with morphine reduced incisional hyperalgesia in wt mice. Incision after saline or escalating morphine treatment upregulated skin IL-1β, IL-6, G-CSF and MIP-1α levels in ppt-A(-/-) and wt mice similarly. However, chronic morphine treatment greatly exacerbated increases in skin nerve growth factor levels after incision, an effect entirely dependent upon intact SP signaling. Additionally, SP dependent upregulation of prodynorphin, NMDA1 and NK1 receptor expression in spinal cord was seen after morphine treatment and incision. A similar pattern was seen for 5-HT3 receptor expression in tissue from dorsal root ganglia. Therefore, SP may work at both central and peripheral sites to enhance nociceptive sensitization after morphine treatment and incision. ⋯ These studies show that SP signaling modulates enhanced nerve growth factor production and changes in neuronal gene expression seen after incision in mice previously exposed to morphine.
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Recently, specific oxidized linoleic acid metabolites (OLAMs) have been identified as transient receptor potential vanilloid 1 (TRPV1) channel agonists that contribute to inflammatory and heat hyperalgesia mechanisms, yet the specific mechanism responsible for OLAM synthesis in sensory neurons is unknown. Here, we use molecular, anatomical, calcium imaging, and perforated patch electrophysiology methods to demonstrate the specific involvement of cytochrome P450 enzymes (CYPs) in the oxidation of linoleic acid leading to neuronal activation and show that this is enhanced under inflammatory conditions. Additional studies evaluated CYP expressions in the native rat trigeminal ganglia (TG) tissue and cultures as well as changes in their expression pattern following the induction of peripheral inflammation. ⋯ In situ hybridization studies demonstrated broad expression pattern of CYP3A23/3A1 and CYP2J4 within TG neurons. Anatomical studies characterized the expression of CYP3A1 and the CYP2J families within TG sensory neurons, including those with TRPV1, with about half of all TRPV1-positive neurons showing more prominent CYP3A1 and CYP2J expression. Together, these findings show that CYP enzymes play a primary role in mediating linoleic acid-evoked activation of sensory neurons and furthermore, implicate the involvement of specific CYPs as contributing to the formation of OLAMs that act as TRPV1 agonists within this subpopulation of nociceptors.