Pain
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The aim of the study was to examine the presence of hyperalgesia to heat stimuli within the zone of secondary hyperalgesia to punctate mechanical stimuli. A burn was produced on the medial part of the non-dominant crus in 15 healthy volunteers with a 50 x 25 mm thermode (47 degrees C, 7 min), and assessments were made 70 min and 40 min before, and 0, 1, and 2 h after the burn injury. Hyperalgesia to mechanical and heat stimuli were examined by von Frey hairs and contact thermodes (3.75 and 12.5 cm2), and pain responses were rated with a visual analog scale (0-100). ⋯ Further, the heat pain response was more intense in the zone of primary hyperalgesia than in the zone of secondary hyperalgesia (P = 0.004), in contrast to the mechanical pain response, which was not significantly different between the two zones of hyperalgesia. In conclusion, secondary hyperalgesia in man is not restricted to mechanical stimuli, as significant hyperalgesia to heat developed within the zone of secondary hyperalgesia to punctate mechanical stimuli. The data, combined with other evidence, suggest differences in the mechanisms accounting for primary hyperalgesia to heat and mechanical stimuli, whereas secondary hyperalgesia to heat and mechanical stimuli may be explained by a common central mechanism.
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Comparative Study
Anti-hyperalgesic and anti-allodynic effects of intrathecal nociceptin/orphanin FQ in rats after spinal cord injury, peripheral nerve injury and inflammation.
We examined the effects of intrathecal nociceptin, the endogenous ligand for the orphan opioid receptor-like receptor, on abnormal pain-related behaviors in rats after carrageenan-induced inflammation and photochemically-induced peripheral nerve or spinal cord ischemic injury. Intrathecal nociceptin dose-dependently alleviated mechanical and cold allodynia-like behavior in the two models of neuropathic pain. The heat hyperalgesia associated with peripheral inflammation was also significantly reduced, although the efficacy of the antihyperalgesic effect of nociceptin in the inflammation model was decreased. ⋯ However, the antinociceptive effect of nociceptin was significantly reduced in rats with peripheral nerve injury. These results indicated that spinally administered nociceptin has anti-allodynic and anti-hyperalgesic effects in animal models of tonic or chronic pain of different origins. Peripheral inflammation and nerve injury may induce spinal plasticity which leads to altered potency and efficacy of nociceptin.
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Randomized Controlled Trial Comparative Study Clinical Trial
Peripheral morphine analgesia in dental surgery.
The recent identification of opioid receptors on peripheral nerve endings of primary afferent neurons and the expression of their mRNA in dorsal root ganglia support earlier experimental data about peripheral analgesic effects of locally applied opioids. These effects are most prominent under localized inflammatory conditions. The clinical use of such peripheral analgesic effects of opioids was soon investigated in numerous controlled clinical trials. ⋯ No serious side effects were reported. Our results show that 1 mg of morphine added to a local anesthetic for dental surgery results in significant improvement of postoperative analgesia. Since the majority of dental surgeries is accompanied with an inflammatory reaction, supplemental morphine may be of benefit for the relief of postoperative dental pain.
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Comparative Study Clinical Trial
Gender differences in pain perception and patterns of cerebral activation during noxious heat stimulation in humans.
The purpose of the present study was to determine whether gender differences exist in the forebrain cerebral activation patterns of the brain during pain perception. Accordingly, positron emission tomography (PET) with intravenous injection of H2(15)O was used to detect increases in regional cerebral blood flow (rCBF) in normal right-handed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm. Each subject was instructed in magnitude estimation based on a scale for which 0 indicated 'no heat sensation'; 7, 'just barely painful' and 10, 'just barely tolerable'. ⋯ However, females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction. Volume of interest comparison (t-statistic) also suggested greater activation of the contralateral insula and thalamus in the females (P < 0.05). These pain-related differences in brain activation may be attributed to gender, perceived pain intensity, or to both factors.
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The ability of athletes to continue to compete despite sustaining painful injury is often interpreted as evidence for the activation of endogenous analgesia mechanisms. However, alterations in perception of noxious stimuli during competition have not yet been systematically investigated. This experiment evaluated experimental pain sensitivity in male and female athletes 2 days before, immediately following, and 2 days after competition. ⋯ Withdrawal latencies to noxious heat also were altered by competition, with finger withdrawal latency decreasing and arm withdrawal latency increasing in most athletes. No changes in pain report were observed across time in non-athlete controls. Competition induces both hyperalgesic and analgesic states that are dependent on the body region tested and pain assessment methodology used.