Pain
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There is emerging evidence that hyperpolarization-activated cation (HCN) channels are involved in the development of pathological pain, including allodynia and hyperalgesia. Mice lacking the HCN isoform 2 display reduced heat but unchanged mechanical pain behavior, as recently shown in preclinical models of acute inflammatory pain. However, the impact of HCN2 to chronic pain conditions is less clear and has not been examined so far. ⋯ We show that chronic inflammation results in an increased expression of HCN2 and causes sensitization in peripheral and spinal terminals of the pain transduction pathway. The contribution of HCN2 to peripheral sensitization mechanisms was further supported by single-fiber recordings from isolated skin-nerve preparations and by conduction velocity measurements of saphenous nerve preparations. Global HCN2 mutants revealed that heat hypersensitivity-unaffected in peripheral HCN2 mutants-was diminished by the additional disruption of central HCN2 channels, suggesting that thermal hyperalgesia under chronic inflammatory conditions is mediated by HCN2 channels beyond primary sensory afferents.
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Multicenter Study
Genome-wide analysis of single nucleotide polymorphisms and copy number variants in fibromyalgia suggest a role for the central nervous system.
Fibromyalgia (FM) is a highly disabling syndrome defined by a low pain threshold and a permanent state of pain. The mechanisms explaining this complex disorder remain unclear, and its genetic factors have not yet been identified. With the aim of elucidating FM genetic susceptibility factors, we selected 313 FM cases having low comorbidities, and we genotyped them on the Illumina 1 million duo array. ⋯ They were followed up, and an intronic deletion in NRXN3 was demonstrated to be associated to female cases of FM with low levels of comorbidities (P=.021, odds ratio [95% confidence interval]=1.46 [1.05-2.04]). Both GWAS and aCGH results point to a role for the central nervous system in FM genetic susceptibility. If the proposed FM candidate genes were further validated in replication studies, this would highlight a neurocognitive involvement in agreement with latest reports.
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Despite recent evidence implicating the nucleus accumbens (NAc) as causally involved in the transition to chronic pain in humans, underlying mechanisms of this involvement remain entirely unknown. Here we elucidate mechanisms of NAc reorganizational properties (longitudinally and cross-sectionally), in an animal model of neuropathic pain (spared nerve injury [SNI]). ⋯ Moreover, interruption of NAc activity (via lidocaine infusion) reversibly alleviated neuropathic pain in SNI animals. Together, these results demonstrate macroscopic (fMRI) and molecular reorganization of NAc and indicate that NAc neuronal activity is necessary for full expression of neuropathic pain-like behavior.
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The current cross-sectional study examined child and adolescent pain severity in relation to various domains of school functioning and, in line with self-determination theory, the potentially protective role of perceived teacher support of child/adolescent autonomy and competence. Data from a large representative sample of Flemish school children and adolescents (N=10650; 50.8% boys; age range 10-21years; mean age=14.33) was collected as part of the World Health Organization (WHO) collaborative Health Behaviour in School-Aged Children (HBSC) survey. Child/adolescent pain severity was graded based on a pediatric pain classification system adapted from that of Von Korff et al. ⋯ However, the association between pain grade and school absenteeism was less pronounced when children perceived their teachers to be highly supportive of competence and autonomy. Furthermore, teacher support of competence appeared to buffer against the harmful effects of severe pain upon instances of bullying experiences at school. Future research directions and implications for school-based interventions are discussed.
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While raised levels of monocyte chemoattractant protein 1 (MCP-1) have been observed in patients with chronic muscle pain, direct evidence for its role as an algogen in skeletal muscle is still lacking. In the rat, MCP-1 induces a dose-dependent mechanical hyperalgesia lasting for up to 6weeks. Following recovery, rats exhibited a markedly prolonged hyperalgesia to an intramuscular injection of prostaglandin E2, hyperalgesic priming. ⋯ The AS treatment attenuated this hyperalgesia, whereas IB4-saporin abolished water-avoidance stress-induced muscle hyperalgesia and prevented stress-induced hyperalgesic priming. These results indicate that MCP-1 induces persistent muscle hyperalgesia and a state of latent chronic sensitization to other algogens, by action on its cognate receptor on IB4+ nociceptors. Because MCP-1 also contributes to stress-induced widespread chronic muscle pain, it should be considered as a player in chronic musculoskeletal pain syndromes.