Articles: hyperalgesia.
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Cold-freeze injury at -4 degrees C to the rat sciatic nerve produces mechanical allodynia and thermal hyperalgesia [M. A. Kleive, P. ⋯ Injury to the rat sciatic nerve induced a significant increase in withdrawal frequency and a significant decrease in withdrawal latency (ANOVA, p<0.05). SYM-2081 and fentanyl significantly reduced these responses (p<0.05). These results suggest that kainate and opioid receptors are involved in the mechanical allodynia and thermal hyperalgesia that develop following cold injury to the sciatic nerve.
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Neuropathic pain is often resistant to opioids, so other medication classes, such as tricyclic antidepressants, anticonvulsants, and local anesthetics, are often used. Central sensitization, or pain 'wind-up', may perpetuate chronic neuropathic pain even when ongoing peripheral sensory input is absent. Wind-up is thought to cause allodynia, hyperalgesia, and hyperpathia. ⋯ No significant side effects were reported. Ketamine Gel may provide clinicians with a new option in the battle against chronic neuropathic pain. Until further information is available and larger trials can be conducted, we can only recommend this type of therapy for refractory cases in which all primary and secondary options have been exhausted.
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Randomized Controlled Trial Clinical Trial
Low-dose lidocaine reduces secondary hyperalgesia by a central mode of action.
Sodium channel blockers are approved for intravenous administration in the treatment of neuropathic pain states. Preclinical studies have suggested antihyperalgesic effects on the peripheral as well as the central nervous system. The objective of this study was to determine mechanisms of action of low-dose lidocaine in experimental induced, secondary hyperalgesia. ⋯ In contrast, capsaicin-induced flare was significantly decreased after both treatments. We conclude that systemic lidocaine reduces pin-prick hyperalgesia by a central mode of action, which could involve blockade of terminal branches of nociceptors. A possible role for tetrodotoxin resistant sodium channels in the antihyperalgesic effect of low-dose lidocaine is discussed.
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Comparative Study Clinical Trial
Age-related differences in the time course of capsaicin-induced hyperalgesia.
The effect of age on hyperalgesia, one of the most common signs of injury, has not been previously examined in humans. A psychophysical study was conducted in 10 young (26.9+/-4.6 years) and 10 older (79. 0+/-5.7 years) healthy volunteers to investigate the effect of age on the development of hyperalgesia induced by topical application of capsaicin (0.1 ml, 5 mg/ml). The capsaicin patch (diameter 2 cm) was applied for 1 h. ⋯ We conclude that, given the same intensity of noxious stimulation, older adults display a similar magnitude of hyperalgesia as younger persons. However, once initiated, punctate hyperalgesia appears to resolve more slowly in older people. This finding may indicate age differences in the plasticity of spinal cord neurons following an acute injury.
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Randomized Controlled Trial Comparative Study Clinical Trial
Pain and allodynia/hyperalgesia induced by intramuscular injection of serotonin in patients with fibromyalgia and healthy individuals.
The aim of this study was to investigate the effect of injection of serotonin (5-HT) into the masseter muscle on pain and allodynia/hyperalgesia. Twelve female patients with fibromyalgia (FM) and 12 age-matched female healthy individuals (HI) participated in the study. The current pain intensity (CPI) and the pressure pain threshold (PPT) of the superficial masseter muscles were assessed bilaterally. 5-HT in one of three randomized concentrations (10(-3), 10(-5), 10(-7) M) or isotonic saline was then injected into either of the two masseter muscles in a double-blind manner. ⋯ In the HI-group pain developed significantly after injection irrespective of whether 5-HT or saline was injected, but significantly more so after 5-HT at 10(-3) M than saline injection. CPI decreased quickly and then remained on a very low level for most of the experiment. 5-HT at both 10(-5) M and 10(-3) M caused a significantly greater decrease of PPT than saline. In conclusion, our results show that 5-HT injected into the masseter muscle of healthy female subjects elicits pain and allodynia/hyperalgesia, while no such responses occur in patients with fibromyalgia.