Pain
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In this paper we compare two innovative models of movement-related pain: tumor-induced nociception following implantation of fibrosarcoma cells into bone and muscle inflammation-induced nociception following injection of the irritant carrageenan into muscle. Importantly, using the grip force test, an assay of movement-related hyperalgesia, both non-malignant and malignant pain are examined in parallel. Movement-related hyperalgesia, known clinically as a specific type of 'breakthrough pain', is a common feature of bone cancer and is thought to be a predictor of poor response to conventional analgesic pharmacotherapy (Bruera et al., 1995, J. ⋯ Tumor-implanted mice with a level of hyperalgesia comparable to that induced by carrageenan required almost three times more morphine (ED(50) 18.5mg/kg) for equivalent attenuation of forelimb hyperalgesia. These animal models of movement-related hyperalgesia may aid in discerning the peripheral and central mechanisms underlying pain that accompanies bone metastases and distinguishing it from the pain associated with muscular inflammation. Importantly, they may also aid in predicting differences in analgesic efficacy in different types of musculoskeletal pain.
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Pharmacological and physiological evidence supports a role for delta (delta) opioid receptors in the nociceptive mechanisms of inflammation. However, few data exist regarding delta opioid receptor expression and localization in such conditions. In this study, we have assessed the distribution and function of delta opioid receptors in the rat spinal cord following induction of chronic inflammation by intraplantar injection of complete Freund's adjuvant (CFA). ⋯ Quantification of immunopositive signal in dendrites revealed a twofold increase in the number of immunogold particles in the ipsilateral dorsal spinal cord of CFA-injected rats compared to the contralateral side and to sham-injected rats. Moreover, the relative frequency of immunogold particles associated with or in close proximity to the plasma membrane was increased in the ipsilateral dorsal spinal cord, indicating a more efficient targeting of delta opioid receptors to neuronal plasma membranes. These data demonstrate that CFA induces an up-regulation and increased membrane targeting of delta opioid receptors in the dorsal spinal cord which may account for the enhanced antinociceptive effects of delta opioid receptor agonists in chronic inflammatory pain models.
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Previous research exploring the relationship between litigation status and the symptoms of the plaintiff has been inconsistent and limited by methodological difficulties. This longitudinal study addressed many of the methodological shortcomings of previous research and examined the relationship between litigation status, employment, depression, pain and disability over the duration of the compensation process. Two hundred chronic back pain participants were selected from patients who attended an initial assessment interview at a pain centre. ⋯ On the other hand participants who were litigating scored higher on all the measures than did participants who were not litigating. There was a significant time effect on all measures but this was qualified on some measures by the interactions of time with litigation status and work status. The present research further demonstrated that both litigation and employment were significant factors influencing recovery from injury.
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Editorial Comment Comparative Study
New directions in research on pain and ethnicity: a comment on Riley, Wade, Myers, Sheffield, Pappas, and Price (2002).