Pain
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Randomized Controlled Trial
Treatment of Na(v)1.7-mediated pain in inherited erythromelalgia using a novel sodium channel blocker.
Mutations in the SCN9A gene leading to deficiency of its protein product, Na(v)1.7, cause congenital indifference to pain (CIP). CIP is characterized by the absence of the ability to sense pain associated with noxious stimuli. In contrast, the opposite phenotype to CIP, inherited erythromelalgia (IEM), is a disorder of spontaneous pain caused by missense mutations resulting in gain-of-function in Na(v)1.7 that promote neuronal hyperexcitability. ⋯ The ability to induce pain in IEM patients was significantly attenuated by XEN402 compared with placebo. XEN402 increased the time to maximal pain induction and significantly reduced the amount of pain (42% less) after induction (P=.014). This pilot study showed that XEN402 blocks Na(v)1.7-mediated pain associated with IEM, thereby demonstrating target engagement in humans and underscoring the use of rare genetic disorders with mutant target channels as a novel approach to rapid proof-of-concept.
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Randomized Controlled Trial
Cognitive manipulation targeted at decreasing the conditioning pain perception reduces the efficacy of conditioned pain modulation.
Although painfulness of the conditioning stimulus (CS) is required for the activation of conditioned pain modulation (CPM), it is still unclear whether CPM expression depends on the objective physical intensity of the CS or the subjective perception of its pain. Accordingly, we cognitively manipulated the perceived CS pain, rendering the physical aspects of the CPM paradigm untouched. Baseline CPM was measured among 48 young healthy male subjects using the parallel paradigm with contact heat as test pain and hand immersion in hot water as CS. ⋯ Pain inhibition under CPM seems to depend on the perceived level of the CS pain rather than solely its physical intensity. Cognitively decreasing the perceived CS pain attenuates CPM magnitude, although a ceiling effect may limit CPM enhancement after cognitively increased CS pain. These findings emphasize the relevance of cognitive mechanisms in determining endogenous analgesia processes in humans.
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Cholecystokinin (CCK) has been suggested to be both pro-nociceptive and "anti-opioid" by actions on pain-modulatory cells within the rostral ventromedial medulla (RVM). One consequence of activation of RVM CCK₂ receptors may be enhanced spinal nociceptive transmission; but how this might occur, especially in states of pathological pain, is unknown. Here, in vivo microdialysis was used to demonstrate that levels of RVM CCK increased by approximately 2-fold after ligation of L₅/L₆ spinal nerves (SNL). ⋯ Spinal administration of naproxen, a nonselective COX-inhibitor, significantly attenuated RVM CCK-induced hindpaw tactile hypersensitivity. RVM-CCK also resulted in a 2-fold increase in spinal 5-hydroxyindoleacetic acid (5-HIAA), a 5-hydoxytryptophan (5-HT) metabolite, as compared with controls, and mechanical hypersensitivity that was attenuated by spinal application of ondansetron, a 5-HT₃ antagonist. The present studies suggest that chronic nerve injury can result in activation of descending facilitatory mechanisms that may promote hyperalgesia via ultimate release of PGE₂ and 5-HT in the spinal cord.
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Investigating dose-dependent effects of placebo analgesia (PA) in laboratory subjects undergoing pain testing, we evaluated 2 hypotheses: (1) greater expectancy for relief produces greater PA, and (2) cued expectancy for relief triggered by a predictive cue leads to more enhanced analgesia than does passive expectancy (no predictive cue). We used conditioning procedures in which 84 subjects experienced reduced stimulation intensity following the application of purported analgesic creams to the 2 experimental fingers, while the control finger received the same levels of stimulation as in the baseline block. The dose of placebos was manipulated by creating 2 levels of expectations for relief. ⋯ Greater expectation for relief led to both (1) greater reductions in the average dependent variable slope (response sensitivity) as a function of stimulus intensity, and (2) greater reductions in average response magnitude. Unexpectedly, uncued expectation led to a slightly larger PA than did cued expectation. The study provided clear evidence that PA can occur in a "dose"-dependent manner, mediated by the levels of expectancy for pain relief.