Pain
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Pain during inflammatory joint diseases is enhanced by the generation of hypersensitivity in nociceptive neurons in the peripheral nervous system. To explore the signaling mechanisms of mechanical hypersensitivity during joint inflammation, experimental arthritis was induced by injection of complete Freund's adjuvant (CFA) into the synovial cavity of rat knee joints. As a pain index, the struggle threshold of the knee extension angle was measured. ⋯ These findings indicate that the ERK signaling is activated in both cell bodies in DRG neurons and peripheral nerve fibers and may be involved in the mechanical sensitivity of the inflamed joint. Furthermore, the phosphorylated ERK-positive neurons co-expressed the P2X3 receptor, and the injection of TNP-ATP, which antagonizes P2X receptors, into the inflamed joint reduced the phosphorylated ERK and the struggle behavior. Thus, it is suggested that the activation of the P2X3 receptor is involved in the phosphorylation of ERK in DRG neurons and the mechanical hypersensitivity of the inflamed knee joint.
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Randomized Controlled Trial Comparative Study
A comparative study of oxycodone and morphine in a multi-modal, tissue-differentiated experimental pain model.
Visceral pain can be difficult to treat with classical mu-opioid agonists and it has been suggested to use opioids with distinct pharmacological profiles. In animal experiments, oxycodone has shown different effects compared to morphine, and clinical observations have shown that oxycodone may occasionally be superior to, e.g., morphine in the treatment of visceral pain. In the current study, we randomised 24 healthy subjects to treatment with either morphine (30 mg), oxycodone (15 mg) or placebo in a crossover study. ⋯ Morphine and oxycodone were equipotent in pain modulation of the skin and muscles, but oxycodone had superior analgesic effect to both morphine and placebo on the mechanical (P<0.001) and thermal (P<0.001) stimulations of the oesophagus. In conclusion, the multi-modal and tissue-differentiated pain model could link findings from animal experiments to clinical findings. A different pharmacological profile of oxycodone compared to that of morphine was shown, and thus oxycodone may be a useful alternative to morphine in the treatment of visceral pain syndromes.
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Cognitive-behavioral factors are considered important in the development of chronic disability and pain in patients with low back pain. In a prospective cohort study of 277 patients undergoing surgery for lumbosacral radicular syndrome, the predictive value of preoperatively measured cognitive-behavioral factors (fear of movement/(re)injury, passive pain coping, and negative outcome expectancies) for disability and pain intensity at 6 weeks and 6 months after surgery was investigated, taking into account the effect of possible confounding variables. Higher levels of cognitive-behavioral factors were found to be associated with a worse outcome at both 6 weeks and 6 months. ⋯ In multiple regression analyses, the cognitive-behavioral factors independently predicted different outcomes. Fear of movement/(re)injury predicted more disability and more severe pain at 6 weeks and more severe pain at 6 months; passive pain-coping strategies predicted more disability at 6 months; and negative outcome expectancies predicted more disability and more severe pain at both 6 weeks and 6 months. The findings support the potential utility of preoperative screening measures that include cognitive-behavioral factors for predicting surgical outcome, as well as studies to examine the potential benefits of cognitive-behavioral treatment to improve surgical outcome.
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Past research has shown that pain catastrophizing contributes to heightened pain experience. The hypothesis advanced in this study was that individuals who score high on measures of pain catastrophizing would also perceive more intense pain in others. The study also examined the role of pain behaviour as a determinant of the relation between catastrophizing and estimates of others' pain. ⋯ Catastrophizing was associated with more accurate pain inferences on only one of three indices of inferential accuracy. The pattern of findings suggests that increasing reliance on pain behaviour as a means of inferring others' pain will not necessarily yield more accurate estimates. Discussion addresses the processes that might underlie the propensity to attend more to others' pain behaviour, and the clinical and interpersonal consequences of perceiving more pain in others.
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Comparative Study
Psychological "resilience" and its correlates in chronic pain: findings from a national community sample.
The display of effective functioning despite exposure to stressful circumstances and/or internal distress is often termed 'resilience'. The study of resilience is believed to provide information about the nature of illness adaptation that is distinct from that obtained via the analysis of clinically impaired groups. In recent years, the concept of resilience has seen only limited exploration in the chronic pain literature. ⋯ An age- and gender-matched non-resilient subsample was then selected who scored high (at least one standard deviation above the mean) on Severity, Interference, and Emotional Burden. The results of a series of comparisons between the resilient and non-resilient groups revealed significant differences favoring resilient individuals in coping style, pain attitudes and beliefs, catastrophizing tendencies, positive and negative social responses to pain, and health care and medication utilization patterns. The findings provide a preliminary foundation for further research aimed at understanding the nature and causal underpinnings of resilience in persons with chronic pain.