Pain
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We investigated the efficacy of local intraplantar (i.pl.) injection of peptide and non-peptide mu-, delta- and kappa-opioid receptor agonists in rat models of inflammatory and neuropathic pain. Locally applied agonists dose-dependently reduced formalin-induced flinching of the inflamed paw and induced antiallodynic and antihyperalgesic effects in sciatic nerve ligation-induced neuropathic pain. These effects were mediated by peripheral opioid receptors localized at the side of tissue/nerve injury, as was demonstrated by selective and non-selective opioid receptors antagonists. ⋯ Furthermore, in order to assess whether adaptations in the expression of opioid genes could underlie the clinical observation of reduced opioid effectiveness in neuropathic pain, we analyzed the abundance of opioid transcripts in the spinal cord and dorsal root ganglia (DRG) during the neuropathy and inflammation. Nerve injury down-regulated mRNA for all types of opioid receptors in the DRG, which is predicted to decrease in the synthesis of opioid receptors to possibly account for the reduced effectiveness of locally administered opioids in neuropathy. The obtained results differentiate inflammatory and neuropathic pain and provide a novel insight into the peripheral effectiveness of opioids in both types of pain.
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The current study examined the Photograph Series of Daily Activities (PHODA) Scale in a sample of chronic low back pain patients with high and low levels of kinesiophobia (pain-related fear). Thirty-three participants completed a modified version of the PHODA (PHODA-M) that obtained ratings of both anticipated pain and harm. Participants' responses on the PHODA-M were compared to predicted and experienced pain and harm ratings collected during a graded-difficulty reaching task. ⋯ In comparison to low fear participants, high fear participants showed larger correlations between pain expectancies for movements depicted in the PHODA and their ratings of predicted and experienced pain on each movement comprising the reaching task. Additionally, high fear participants showed larger associations between the perceived harmfulness of PHODA activities and predicted and experienced harm ratings in response to the reaching task. Implications for the findings are discussed.
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Direct application of cannabinoids to the medullary dorsal horn (MDH) inhibits lamina V nociceptive neurons. The present study compared the effect of the cannabinoid receptor agonist, WIN 55,212-2 (WIN-2) on the activity of lamina I and lamina V MDH neurons using extracellular single unit recording in anesthetized rats. Activity evoked by a contact thermode was measured before and after local application of WIN-2 (0.5-2.0 microg/microl) to the brainstem. ⋯ In separate experiments, the effect of intrathecal administration of WIN-2 to the MDH on head withdrawal latencies elicited by fast and slow heat ramps applied to the whisker pad was assessed in lightly anesthetized rats. Head withdrawal latencies elicited by slow but not by fast heat stimulation were increased by WIN-2. Taken together, these results emphasize the importance of lamina I neurons in the control of a nociceptive heat-evoked reflex.
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Musculoskeletal pain that affects multiple body sites is typically regarded as comorbidity to single-site pain. Pain present in multiple sites, however, is more severe and disabling compared to single-site pain. This study aimed to prospectively investigate the change in the number of pain sites over 14years, in addition to identifying predictors of multi-site pain. ⋯ However, only sex, age, sleep quality, and educational level remained significant in the final multivariate model after controlling for the number of pain sites at baseline. The final model explained 35% of the variance, of which nearly 80% was accounted for by the number of pain sites at baseline. As the pattern of reporting the number of pain sites appears relatively stable across adulthood and baseline multi-site pain demonstrated strong predictive utility, studies investigating the occurrence of multi-site pain in children and adolescents are recommended to determine potential causal factors contributing to the early course and development of multi-site musculoskeletal pain.