Pain
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Previous studies from our laboratory have demonstrated that both chronic inflammatory pain, induced by intraplantar injection of complete Freund's adjuvant (CFA), and prolonged (48 h) stimulation of mu-opioid receptors (muOR) by systemic administration of a variety of selective agonists, resulted in enhanced plasma membrane targeting of delta-opioid receptors (deltaOR) in neurons of the dorsal spinal cord. To determine whether deltaOR trafficking induced by chronic inflammation was dependent on the activation of muOR, we investigated by immunogold cytochemistry the effects of intraplantar CFA injection on the plasma membrane density of deltaOR in muOR knockout (KO) mice. In untreated wild-type (WT) mice, only a small proportion of deltaOR was associated with neuronal plasma membranes in the dorsal horn of the spinal cord. ⋯ This increase in the membrane density of deltaOR was likely due to a recruitment of receptors from intracellular stores since no difference in the overall deltaOR immunolabeling density was evident between CFA-treated and untreated mice. Most importantly, the CFA-induced changes in deltaOR plasma membrane insertion seen in WT animals were not present in the spinal cord of muOR KO mice. These results demonstrate that the integrity of muOR is necessary for CFA-induced changes in deltaOR trafficking to occur and suggest that these changes could be elicited by stimulation of muOR by endogenous opioids released in response to chronic inflammatory pain.
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Melatonin, its agonists/antagonists were administered intrathecally (i.t.) before/after intradermal injection of capsaicin. Capsaicin produced an increase in the paw withdrawal frequency (PWF) in the presumed area of secondary mechanical allodynia and hyperalgesia. Melatonin agonists in the absence of a capsaicin injection decreased the PWF significantly, whereas melatonin antagonists given intrathecally alone were ineffective in the absence of a capsaicin injection. ⋯ In spinal rats, the data showed comparable effects of melatonin analogs on capsaicin-induced secondary mechanical hyperalgesia. Animal motor function tested by 'activity box' showed that motion activity was not affected by i.t. melatonin or its antagonist. These results suggest that activation of the endogenous melatonin system in the spinal cord can reduce the generation, development and maintenance of central sensitization, with a resultant inhibition of capsaicin-induced secondary mechanical allodynia and hyperalgesia.
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Shoulder complaints are common and have an unfavourable outcome in many patients. Only 50% of all new episodes of shoulder disorders end in complete recovery within 6 months. There is no consensus about prognostic indicators that can identify patients at high and low risk of chronicity. ⋯ There is strong evidence that high pain intensity predicts a poorer outcome in primary care populations and that middle age (45-54) is associated with poor outcome in occupational populations. There is moderate evidence that a long duration of complaints, and high disability score at baseline predict a poorer outcome in primary care. These results need to be interpreted with caution because of the small number of studies on which these conclusions are based, and the large heterogeneity among studies regarding follow-up, outcome measures, and analysis.
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This study examined the relationship between catastrophizing and patient-perceived partner responses to pain behaviors. The Catastrophizing subscale of the Cognitive Coping Strategy Inventory and the West Haven-Yale Multidimensional Pain Inventory were completed by 62 adult chronic pain patients. Consistent with past research, catastrophizing and patient-perceived solicitous partner behaviors were positively correlated with negative pain outcomes. ⋯ However, catastrophizing was not related to perceived solicitous partner behavior in this study. Rather, catastrophizing was associated with perceived punishing partner responses. Implications are that catastrophizing and perceived solicitous partner behaviors are independently associated with pain and that catastrophizing may not be reinforced by empathy from significant others.
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While a variety of cultural, psychological and physiological factors contribute to variability in both clinical and experimental contexts, the role of genetic factors in human pain sensitivity is increasingly recognized as an important element. This study was performed to evaluate genetic influences on variability in human pain sensitivity associated with gender, ethnicity and temperament. Pain sensitivity in response to experimental painful thermal and cold stimuli was measured with visual analogue scale ratings and temperament dimensions of personality were evaluated. ⋯ Female European Americans with the TRPV1 Val(585) Val allele and males with low harm avoidance showed longer cold withdrawal times based on the classification and regression tree (CART) analysis. CART identified gender, an OPRD1 polymorphism and temperament dimensions of personality as the primary determinants of heat pain sensitivity at 49 degrees C. Our observations demonstrate that gender, ethnicity and temperament contribute to individual variation in thermal and cold pain sensitivity by interactions with TRPV1 and OPRD1 single nucleotide polymorphisms.