Articles: hyperalgesia.
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Wallerian degeneration with macrophage influx and production of proinflammatory cytokines is a critical factor in the development of hyperalgesia in animal models of neuropathic pain. We hypothesized that in the mouse strain with delayed Wallerian degeneration, the C57BL/Wld mouse, the temporal course of mechanical allodynia and thermal hyperalgesia as well as the temporal profile of cytokine expression after nerve injury would differ from normal mice. Here we used the model of chronic constriction injury of the sciatic nerve (CCI) to study the correlation of pain related behavior with peripheral nerve de- and regeneration and concomitant cytokine production. ⋯ Endoneurial tumor necrosis factor-alpha (TNF)-like immunoreactivity increased rapidly in normal mice but did so with a delayed time course in C57BL/Wld mice. In addition, the duration of mechanical allodynia was significantly prolonged in C57BL/Wld mice as compared to C57BL/6 mice, in accordance with the delay in regeneration of sensory nerve fibers in these mice. These results suggest that macrophage invasion and production of TNF may influence the development of thermal hyperalgesia and that regenerative activity is linked to mechanical allodynia in peripheral mononeuropathy.
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Temporal summation of pain occurs when repeated stimuli become increasingly painful in spite of unchanged stimulus intensity. Summation can be quantified as the difference in pain between the first and the last stimulus in a train of stimuli. The aim of the study was to compare temporal summation of pain in normal skin with summation of pain in skin with primary and secondary hyperalgesia evoked by a heat injury. ⋯ Temporal summation at high stimulus intensities was more pronounced than at lower intensities (P < 0.0002). We found no correlation between either temporal summation and area of secondary hyperalgesia, or temporal summation and pain intensity during the induction of heat injury. We conclude that the development of primary and secondary mechanical hyperalgesia after heat injury in man was not associated with changes in temporal summation of painful electrical stimuli.
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We previously reported that ketamine analgesia in acute pain was produced by the activation of the monoaminergic descending inhibitory system. Recent studies have confirmed that the NMDA receptor antagonists attenuate the hyperalgesia in neuropathic pain. In this study, we investigated the suppressive effects of a clinically available NMDA antagonist, ketamine, and the mechanisms of its effects on neuropathic pain in rats with peripheral mononeuropathy. ⋯ The CCI rats showed increased NE and 5HT concentrations on both ligated and unligated sides of spinal dorsal horn, compared with shamoperated rats. IP ketamine (50 mg.kg-1) in the CCI rats did not boost the spinal NE or 5HT levels. These results indicate that the anti-hyperalgesic effect of ketamine is derived from a direct action on the spinal cord, but not from the activation of monoaminergic descending inhibitory systems.
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J. Pharmacol. Exp. Ther. · Feb 1998
Repetitive opioid abstinence causes progressive hyperalgesia sensitive to N-methyl-D-aspartate receptor blockade in the rat.
The opioid abstinence syndrome is associated with spinal excitatory amino acid (EAA) release, hyperalgesia and long-term changes in dorsal horn cellular excitability. N-Methyl-D-aspartate (NMDA) receptor antagonism attenuates opioid tolerance but also blocks EAA release during abstinence. This study examines the effect of repetitive abstinence, and NMDA receptor antagonism during abstinence, on thermal nociceptive thresholds and spinal tolerance. ⋯ Hyperalgesia was most pronounced in groups subjected to repetitive abstinence, and least evident in groups in which continuous infusion was maintained or in which MK was administered during abstinence. MK administered during abstinence did not prevent tolerance. These results show that repetitive opioid abstinence is associated with progressive hyperalgesia mediated via NMDA receptor activation, but that NMDA receptor antagonism during such periods of abstinence does not prevent progressive opioid tolerance.
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The aim of the study was to examine reproducibility of primary and secondary hyperalgesia in a psychophysical model of human inflammatory pain. Mild burns were produced on the crura of 12 volunteers with a 50 x 25 mm thermode (47 degrees C, 7 min). Assessments of (i) cold and warm detection thresholds, (ii) mechanical and heat pain thresholds, (iii) pain to heat (43 degrees C and 45 degrees C, 5 s), (iv) secondary hyperalgesia, and (v) skin erythema were made 1.75 and 0.5 h before, and 0, 1, 2, 4, and 6 h after a burn injury. ⋯ Habituation to the painful stimuli was demonstrated by significantly higher pain thresholds and lower pain responses on the second and third day of the study. The burn model is a sensitive psychophysical model of acute inflammatory pain, when cross-over designs and within-day comparisons are used, and the model is suitable for double-blind, placebo-controlled studies of analgesics. In similar models, we recommend that analgesic and placebo are evenly divided between right and left sides and study days.