Pain
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Randomized Controlled Trial Comparative Study
Effects of morphine on the experimental illusion of pain produced by a thermal grill.
We compared the effects of systemic morphine on normal (heat and cold) pain and paradoxical burning pain evoked by the simultaneous application of innocuous warm and cold stimuli to the skin. Twelve healthy volunteers participated in a randomised, double-blind, cross-over study to compare the effects of intravenous administration of morphine (0.025 or 0.1mg/kg) or placebo (saline). Stimuli were applied to the palm of the right hand with a thermode ("thermal grill") composed of six bars, whose temperatures were controlled by Peltier elements. ⋯ No differences were observed for non-painful thermal sensations. The paradoxical burning pain evoked by a thermal grill can be modified pharmacologically by analgesics and share some mechanisms with normal pain. This unique experimental "illusion of pain" may represent a new model to test analgesics in healthy volunteers.
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Comparative Study
The role of heterosynaptic facilitation in long-term potentiation (LTP) of human pain sensation.
Long-term potentiation (LTP) of nociceptive synaptic transmission induced by high-frequency electrical stimulation (HFS) predominantly modulates natural somatosensory perceptions mediated by Adelta- and Abeta-fibers in humans at the site of conditioning stimulation. The relative contribution of homo- and heterosynaptic mechanisms underlying those perceptual changes remained unclear. We therefore compared changes of the somatosensory profile between a conditioned skin site (homotopic zone) and an area adjacent to conditioning HFS (heterotopic zone). ⋯ Moreover, a small decrease of thresholds to blunt pressure was found at both zones (p<0.05). Pain summation (windup ratio), mechanical detection threshold as well as vibration detection threshold remained unchanged. Because none of the changes in sensory parameters was unique for the site of conditioning stimulation, these data suggest that heterosynaptic interactions are the predominant mechanism of LTP in nociceptive pathways.
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Previously, we demonstrated that placebo analgesia (PA) accompanies reductions in neural activity during painful stimulation. This study investigated areas of the brain where the neural activity was increased during PA. The literature has associated PA with two potential mechanisms of action; one sustained (e.g., engaged for the duration of PA), the other, transitory (e.g., a feedback mechanism). ⋯ Conversely, brain regions with transient activity included linguistic centers in the left hemisphere and frontal regions of the right hemisphere generally associated with executive functioning. Together, these mechanisms likely engage analgesic processes and then simply monitor the system for unexpected stimuli, effectively liberating resources for other processes. Identifying brain regions associated with pain-modulation with different temporal profiles is consistent with the multidimensionality of PA and highlights the need for continued investigation of this construct.
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Chronic pain is a public health problem with high impact on various population segments. There are few population studies with the aim of delineating the profile of the chronic pain patient, and generating data for actions to prevent, control and minimize the problem. The aim of this study was to estimate the prevalence of chronic pain in the population of Salvador, Bahia, Brazil and identify independent predictors associated with this morbidity. ⋯ Among the studied factors, in the gross analysis, the following were shown to be associated with chronic pain: conjugal situation, smoking, excessive alcohol consumption, presence of central obesity and age, all with p<0.05. In the multivariate analysis, female sex, smoking, excessive alcohol consumption, and age were sustained as independent predictors. The presence of chronic pain was predominant in women, the elderly, smokers or ex-smokers and excessive alcohol consumers.
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Accumulating evidence points to significant cognitive disruption in individuals with Fibromyalgia Syndrome (FMS). This study was carried out in order to examine specific cognitive mechanisms involved in this disruption. Standardized experimental paradigms were used to examine attentional function and working memory capacity in 30 women with FMS and 30 matched controls. ⋯ These findings point to disrupted working memory as a specific mechanism that is disrupted in this population. The results of this study suggest that pain in FMS may play an important role in cognitive disruption. It is likely that many factors, including disrupted cognition, play a role in the reduced quality of life reported by individuals with FMS.