Pain
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The present study was designed to further characterize hypnotic analgesia and particularly to examine whether the effects are due to a selective alteration of pain perception and are organized somatotopically. Thirty-two healthy volunteers participated in this study. Thermal detection thresholds for warmth and cool stimuli and heat pain thresholds were measured at both the upper and lower left limbs by means of a thermotest. ⋯ Mean detection thresholds for warmth and cool stimuli were also altered at both the lower and upper limbs during hypnosis, but these modifications were correlated neither with susceptibility nor with the changes in heat pain threshold. These results indicate that hypnotic suggestions can selectively and somatotopically alter pain sensation in highly susceptible subjects. It is also suggested, however, that suggestions of analgesia can induce selective alterations of pain perception in poorly susceptible subjects, although these effects did not appear to be localized 'appropriately'.
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This study reports chronic pain prevalence in a randomly selected sample of the adult Australian population. Data were collected by Computer-Assisted Telephone Interview (CATI) using randomly generated telephone numbers and a two-stage stratified sample design. Chronic pain was defined as pain experienced every day for three months in the six months prior to interview. ⋯ Within the subgroup of respondents reporting chronic pain, the presence of interference with daily activities caused by pain was significantly associated with younger age; female gender; and not having private health insurance. There were strong associations between having interfering chronic pain and receiving disability benefits (adjusted OR=3.31, P<0.001) or being unemployed due to health reasons (adjusted OR=7.94, P<0.001, respectively). The results show that chronic pain impacts upon a large proportion of the adult Australian population, including the working age population, and is strongly associated with markers of social disadvantage.
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A growing body of evidence supports a nicotinic cholinergic approach to pain management, as neuronal nicotinic receptor agonists have shown efficacy across animal models of both inflammatory and neuropathic pain. However, most of these investigations have focused on the spinal system, and there is to date no report of nicotinic receptor-mediated antinociception in any pain model involving the trigeminal field of innervation. Thus, the purpose of the present studies was to evaluate whether the neuronal nicotinic receptor agonist epibatidine possesses antihyperalgesic activity in the formalin model of facial pain. ⋯ Finally, pretreatment with the selective neuronal nicotinic receptor antagonist mecamylamine completely abolished the antihyperalgesic effect of epibatidine in both phases. Taken together, these studies demonstrate that in both the acute and tonic phases of the formalin model of facial pain, epibatidine produces a neuronal nicotinic receptor-mediated antihyperalgesia that is both dose- and time-dependent. These results support the rationale for exploring the clinical efficacy of nicotinic agonists as analgesics to treat certain types of trigeminal pain in humans.
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Peripheral inflammation induced with a knee joint injection of a mixture of kaolin/carrageenan (k/c) produces primary and secondary hyperalgesia. Inflammatory pain is thought to involve a variety of transmitters released from nerve terminals, including amino acids, substance P (SP) and calcitonin gene-related peptide (CGRP). In the present study, mice deficient in the calcitonin/alpha CGRP gene (CGRP(-/-)) displayed normal responses to noxious stimuli. ⋯ The CGRP(-/-) mice also had a prolonged rather than a shortened response latency in the hot-plate test 4 h after knee joint injection of k/c. Immunohistological study showed that CGRP-like immunoreactivity (CGRP-LI) was absent in the spinal cord and dorsal root ganglia taken from the CGRP(-/-) mice. These results indicate that endogenous CGRP plays an important role in the plastic neurogenic changes occurring in response to peripheral inflammatory events including the development of nociceptive behaviors.
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Anatomical studies demonstrate the presence of glutamate receptors on unmyelinated axons in peripheral cutaneous nerves. Pharmacological studies show that intraplantar injection of glutamate or glutamate agonists in the glabrous skin results in nociceptive behaviors. The present study describes a novel in vitro skin-nerve preparation using the glabrous skin from the rat hindpaw. ⋯ Exposure of A delta or C fibers to glutamate did not result in a decrease in von Frey thresholds. These data provide a physiological basis for the nociceptive behaviors that arise following intraplantar injection of glutamate or glutamate agonists. Furthermore, demonstration of glutamate-induced excitation and heat sensitization of nociceptors indicates that local or topical administration of glutamate receptor antagonists may have therapeutic potential for the treatment of pain.