The journal of pain : official journal of the American Pain Society
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Women have a higher prevalence of fibromyalgia and myofascial pain than men, but sex differences in muscle pain are inconsistently detected. We examined sex differences in ratings and effects of recalled and experimentally-induced muscle pain. In study 1 (n = 188), participants completed a questionnaire about recalled muscle pain. In study 2 (n = 55), participants described muscle pain from an exercise stimulus across 3 days by telephone. Muscle pain ratings, self-care behaviors for muscle pain, and effects of muscle pain on activities were measured. No significant sex differences were found except that women tended to view exercise as more effective for decreasing muscle pain than men (F (1, 187) = 5.43, P = .02, eta(2) = .03), fewer women performed exercise for induced muscle pain than men, and women's activity interference was significantly higher than men's at the third day after exercise (F (2, 42) = 6.54, P = .01, eta(2) = .14). These findings support the absence of meaningful sex differences in muscle pain ratings. However, additional investigations are needed that consider the daily activities completed by people and the prevalence and incidence of performing a wide range of self-care behaviors for pain. ⋯ These studies support that sex differences are not present in recalled and experimentally-induced muscle pain ratings. Therefore, we must be cautious about generalizing the musculoskeletal pain literature to muscle pain. Additional research is needed to interpret potential sex differences in self-care behaviors for muscle pain and activity interference from muscle pain.
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The objective of the present study was to evaluate the time course of changes in peripheral nerve insulin receptor (IR) signaling and compare observed findings with behavioral responses to noxious mechanical and thermal stimuli in streptozotocin (STZ)-diabetic rats over 12 weeks of diabetes. Diabetic rats developed mechanical hyperalgesia, as indicated by decreased paw withdrawal thresholds to mechanical stimuli that were detectable after 2 weeks of diabetes; they also developed thermal hypoalgesia, as indicated by increased tail flick latencies to thermal stimuli that were detectable at 1 week of diabetes. Western blot analysis revealed decreased phosphorylated: total IR protein ratio that was detectable as early as 2 weeks of diabetes, whereas phosphorylated:total Akt protein ratio was decreased at 2 weeks and increased at 12 weeks of diabetes with unchanged PI-3K protein levels. To our knowledge, the present study is the first to demonstrate that impaired peripheral nerve IR signaling, as indicated by decreased phosphorylated:total IR protein ratio, coincides with early mechanical hyperalgesia and thermal hypoalgesia in STZ-diabetic rats. This finding may improve understanding of how altered pain sensation develops rapidly in this model. ⋯ This study examined peripheral nerve IR signaling during the early course of altered nociception in STZ-diabetic rats. In diabetic rats, impaired peripheral nerve IR signaling is observed shortly after STZ injection, as is altered nociception. This finding suggests a possible role of impaired IR signaling in diabetic sensory neuropathy.
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We have recently demonstrated that inferior alveolar nerve and mental nerve (branches of the mandibular nerve) injury from rats serves as a valid trigeminal neuropathic pain model. In these animals, we found that neuronal loss of trigeminal ganglion (TG) was not correlated with pain hypersensitivity. In this study, we examined changes of transient receptor potential vanilloid 1 (TRPV1) expression in the injured and uninjured TG neurons using immunohistochemical analysis at 3 days after surgery, the time point where we observed significant pain hypersensitivity. Injured neurons were identified by positive immunoreactivity for activating transcription factor 3 (ATF3). ATF3 immunoreactivity was exclusively observed in the nuclei of subpopulation of ipsilateral mandibular TG neurons, whereas no ATF3 expression was found in the naive and contralateral TG neurons. Interestingly, the expression of TRPV1 was increased in the uninjured ipsilateral maxillary TG neurons as well as in the uninjured ipsilateral mandibular TG neurons. The upregulation of TRPV1 and ATF3 expression returned to the basal level at 60 days after surgery. Our results demonstrate that trigeminal sensory nerve injury induced differential changes in TRPV1 expression of the injured and uninjured TG neurons. The upregulation of TRPV1 in uninjured TG neurons may play an important role in pain hypersensitivity after trigeminal nerve injury. ⋯ The TRPV1 is a well-known pain transducer molecule and plays crucial roles in the perception of inflammatory and thermal pain. This article presents that TRPV1 expression was increased in uninjured neurons rather than injured neurons after peripheral nerve injury. The upregulation of TRPV1 in uninjured neurons may be associated with the development of neuropathic pain. TRPV1 might be a potential target for the treatment of neuropathic pain.
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Little is known about how a child's experience of pain affects his or her parents. Using a vignette methodology, this study investigated the emotional responses of parents who were asked to imagine different painful situations that their child might experience. A sample of 650 parents of school children (325 mothers; 325 fathers) read 8 short stories/vignettes about their child, which varied in terms of type of situation (pain vs other stressful situation), intensity (high vs low), and frequency of occurrence (high vs low). The role of individual differences in parental catastrophizing about their child's pain, catastrophizing about their own pain, dispositional empathy, and gender was also investigated. Parents' dispositional empathy was found to have an impact on parental distress and concern for their child. Catastrophizing about their child's pain had a unique contribution to parents' emotional responses to the vignettes describing their child in pain, beyond the influence of other variables. The impact of parental catastrophizing about their child's pain was most pronounced for parental distress, probably reflecting the high threat value that they attribute to their child's pain. The findings are discussed within recent models of empathy and pain, delineating possible relationships with parents' behavioral responses to their child's pain. ⋯ This vignette study found preliminary evidence for the importance of parent characteristics, beyond situational characteristics, in parental emotional responses to their child's pain. The findings provide indications for the processes implied in parental helping behavior.
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Randomized Controlled Trial Multicenter Study Clinical Trial
Efficacy of dronabinol as an adjuvant treatment for chronic pain patients on opioid therapy.
We assessed the efficacy of dronabinol (Marinol capsules; Solvay Pharmaceuticals, Brussels, Belgium), a synthetic Delta(9)-THC (tetrahydrocannabinol), in 30 patients taking opioids for chronic pain to determine its potential analgesic effects as an adjuvant treatment. Phase I of this 2-phase study was a randomized, single-dose, double-blinded, placebo-controlled, crossover trial in which subjects were randomly administered either 10 mg or 20 mg of dronabinol or identical placebo capsules over the course of three, 8-hour visits. Baseline self-report measures, hourly ratings of pain intensity, pain relief, pain bothersomeness, treatment satisfaction, mood, side effects, and blood serum levels were obtained. Phase II was an extended open-label titrated trial of dronabinol as add-on medication to patients on stable doses of opioids. Results of the Phase I study showed that patients who received dronabinol experienced decreased pain intensity and increased satisfaction compared with placebo. No differences in benefit were found between the 20 mg and 10 mg doses. In the Phase II trial, titrated dronabinol contributed to significant relief of pain, reduced pain bothersomeness, and increased satisfaction compared with baseline. The incidence of side effects was dose-related. Overall, the use of dronabinol was found to result in additional analgesia among patients taking opioids for chronic noncancer pain. ⋯ This study examines the effect of adding a cannabinoid to the regimen of patients with chronic pain who report significant pain despite taking stable doses of opioids. The results of our preliminary study suggest that dronabinol, a synthetic THC, may have an additive effect on pain relief.