Articles: hyperalgesia.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Aug 2006
Comparative StudyPersistent pain model reveals sex difference in morphine potency.
Central or systemic administration of agonists directed at the mu or delta opiate receptors generally produce a greater degree of analgesia in males than in females. To date, most studies examining sex-based differences in opioid analgesia have used acute noxious stimuli (i.e., tail-flick and hot plate test); thus the potential dimorphic response of centrally acting opiates in the alleviation of persistent inflammatory pain is not well established. In the present study, right hind paw withdrawal latency (PWL) to radiant thermal stimuli was measured in intact male and cycling female Sprague-Dawley rats before and after unilateral hind paw injection of the inflammatory agent complete Freund's adjuvant (CFA). ⋯ At all morphine doses administered, both the antihyperalgesic effects of morphine in the inflamed animals and the antinociceptive effects of morphine in control animals were significantly greater in males compared with females. Similarly, in males, the antihyperalgesic effects of morphine increased significantly at 7-21 days post-CFA; no significant shift in morphine potency was noted for females. These studies demonstrate sex-based differences in the effects of morphine on thermal hyperalgesia in a model of persistent inflammatory pain.
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J. Neurosci. Methods · Jul 2006
Characterization of hind paw licking and lifting to noxious radiant heat in the rat with and without chronic inflammation.
The paw withdrawal latency to thermal radiant heat stimuli is a widely used nociceptive measure to study hyperalgesic mechanisms. In the present study, in addition to the paw withdrawal latency, two behavioral components of pain behaviors, paw licking and paw lifting have been characterized and quantified. The thermal stimuli were successively applied to the plantar surface of the rat hind paws and recorded the behavioral responses to each of the stimuli. ⋯ The paw withdrawal latency decreased in inflamed rats in comparison with control rats. These data informs that noxious radiant heat specifically evokes the frequency of paw lifting behavior in normal physiological condition, and paw licking behavior in a pathological inflammatory condition. These findings suggest that in addition to the measurement of PWL, scoring of paw licking and lifting behaviors will improve the sensitivity of this pain test.
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Hyperbaric oxygen therapy has been used to treat a variety of ailments from carbon monoxide poisoning to fibromyalgia. The purpose of this experiment was to explore the effect of hyperbaric oxygen treatment on carrageenan-induced inflammation and pain in rats. Hyperbaric oxygen treatment significantly decreased inflammation and pain following carrageenan injection. Clinically hyperbaric oxygen may be used in situations where NSAIDS are contraindicated or in persistent cases of inflammation.
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Intradermal capsaicin is a human pain model that produces reliable pain and sensitization. This model facilitates controlled testing of analgesic efficacy via a crossover design while minimizing confounding variables in clinical pain states and retaining sufficient power with small samples. ⋯ The 10 and 100 microg capsaicin doses produced robust pain measures across a range of modalities, and lower doses produced minimal effects. Whereas most studies use 100 microg, using a lower dose is reasonable and may facilitate detection of subtle analgesic effects--particularly with nonopioid analgesics--and drugs can be tested in lower doses, minimizing adverse side effects.
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Controlled Clinical Trial
Comparison of dynamic (brush) and static (pressure) mechanical allodynia in migraine.
Allodynia has been described in migraine but has not been fully investigated for the different sensory modalities. The aim of this study was to compare the prevalence of dynamic (brush) and static (pressure) mechanical allodynia in migraine patients and to suggest a practical method of testing them in a clinical setting. Patients with International Headache Society-defined episodic migraine (EM) or with transformed migraine (TM) as defined by Silberstein and Lipton were prospectively recruited from the Jefferson Headache Center out-patient clinic. ⋯ The incomplete, although considerable, overlap between BA and PA suggests that allodynia to different sensory modalities is associated with sensitization of different neuronal populations. Because PA was more common than BA, it may be a more sensitive indicator of allodynia in migraine. PA can be tested clinically in a practical and systematic manner.