Pain
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Recent animal studies using stress-induced analgesia have suggested a general age-related decline in endogenous pain inhibitory systems. The aim of the current study was to examine age-related differences in the magnitude of endogenous analgesia in human volunteers, using psychophysical measures of neuroselective electrical, and thermal CO(2) laser induced pain thresholds, before, immediately after and 1 h after repeated cold water immersion of the hand. Sensory detection thresholds did not differ between age groups indicating that the functional integrity of primary afferent sensory fibres appears to be intact in older people. ⋯ This effect was relatively transient with thresholds returning to baseline within 1 h. The magnitude of analgesic response, however, was found to be significantly less in older people. Age differences in the efficacy of endogenous analgesic systems may be expected to reduce the ability of older adults to cope with severe persistent pain states and may help explain some of the variation in the literature on pain report.
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Comparative Study
Comparison of autotomy behavior induced in rats by various clinically-used neurectomy methods.
When a peripheral nerve is cut, a neuroma develops at its proximal end. Nerve-end neuromas are known to be a source of ectopic sensory input. In some humans this input may cause spontaneous and evoked neuropathic pain. ⋯ The differing scores of autotomy caused by these neurectomy methods may derive from different properties of the injury discharge produced by these methods at the time of nerve cut. Our results raise the possibility that a higher incidence of neuropathic pain or related sensory disorders in humans may be expected following cryosurgical and electrocut neurectomies. If validated by further studies, neurectomy methods eliciting lower incidence of autotomy, and sensory disorders in models not based on autotomy may produce lower levels of neuropathic pain in humans.
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Randomized Controlled Trial Clinical Trial
Effect of pre- or post-traumatically applied i.v. lidocaine on primary and secondary hyperalgesia after experimental heat trauma in humans.
Hyperalgesia on intradermal capsaicin application can be attenuated by systemic application of local anesthetics. We tested whether low doses of local anesthetics applied pre- or post-traumatically can reduce heat trauma-induced primary and secondary hyperalgesia in humans. Six healthy volunteers consented to the randomized, double-blind, and cross-over designed study. ⋯ Thus, local anesthetics at concentrations that do not block nerve conduction substantially affect ongoing central changes in pain processing that are induced by a real tissue trauma. A significant preemptive effect could not be demonstrated. The anti-hyperalgesic effect of lidocaine is likely based on action of central (spinal) sites, but peripheral sites may also be addressed.
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Possible role of inflammatory mediators in tactile hypersensitivity in rat models of mononeuropathy.
Peripheral hypersensitivity (hyperalgesia and allodynia) are common phenomena both in inflammatory and in neuropathic pain conditions. Several rat models of mononeuropathy (Bennett, Seltzer and Gazelius models) display such symptoms following partial injury to the sciatic nerve. Using immunohistochemistry and behavioral tests, we investigated inflammatory cell and cytokine responses in the sciatic nerve 14 days after injury created in these different models as well as after axotomy. ⋯ Our findings indicate that the considerable increase in monocytes/macrophages induced by a nerve injury results in a very high release of IL-6 and TNF-alpha. This may relate to the generation of tactile allodynia/hyperalgesia, since there was a clear correlation between the number of ED-1 and IL-6-positive cells and the degree of allodynia. It is possible that measures to reduce monocyte/macrophage recruitment and the release of pro-inflammatory interleukins after nerve damage could influence the development of neuropathic pain.