Pain
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Despite the prominence of fear-avoidance models of chronic pain, there is a paucity of research regarding the origins of pain-related fear. Based on the premise that insecure attachment could be a developmentally based origin of elevated fear of pain, associations between adult attachment dimensions and constructs included in fear-avoidance models of chronic pain were investigated. Consistent with Bartholomew and Horowitz's [Bartholomew K, Horowitz LM. ⋯ The model of self dimension had significant positive associations with each of the fear-avoidance constructs. The model of others dimension had a significant positive association with pain catastrophizing, but was not significantly associated with fear of pain and pain hypervigilance. Future research directions and potential clinical implications are discussed.
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The experience of pain has been documented in small studies of individuals with multiple sclerosis (MS). The present study examines the prevalence of persistent pain and uncomfortable sensations among participants in the large North American Research Committee on MS (NARCOMS) Patient Registry. Registrants (10,176) responded to a questionnaire on pain and 7579 reported experiencing some level of pain during the month prior to the survey. ⋯ About one-third of the patients with moderate pain and 18% of those with severe pain reported no consultations for their pain. The effects of pain severity were fully evident in the respondents' daily life, their work, mood, recreational activities and enjoyment of life. Our results indicate that the high prevalence of MS-related severe pain, low satisfaction with management of intense pain, and the perceived interference with quality of life indicators necessitate greater attention by healthcare providers to the management of pain and uncomfortable sensations in the MS population.
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The contribution of the amygdala to neuropathic pain processing in animals has not been clearly acknowledged. To assess the relative contribution of amygdala GABA-A receptors in mediating sensory-discriminative and affective-motivational pain components, the GABA-A receptor agonist muscimol and the antagonist bicuculline (both 10-25 ng/microl) were administered by acute bilateral injection directly into the central amygdala in rats with a chronic constriction injury (CCI). Escape/avoidance behaviour reflecting the affective-motivational dimension of pain was measured using a light/dark chamber in combination with suprathreshold nociceptive stimulation, and was defined as a shift from the 'non-aversive' dark area of the chamber to the 'aversive' light area. ⋯ Motility behaviour was unaffected by injection of either drug as determined in the open field test. Thus, amygdala GABA-A receptors appear to play an important role in sensory and especially affective pain processing in neuropathic rats. Furthermore, after nerve injury reflex nociceptive behaviours appear to be under tonic control by descending inputs, which originate from or are modulated within the amygdala.
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Our previous recordings from dorsal root ganglion and spinal lamina V neurons from TRPV1-mutant mice showed dramatic decreases in responses to temperatures near the activation threshold of this channel (43-49 degrees C). Somewhat unexpectedly, we only observed behavioral deficits in these mice at higher temperatures (50-58 degrees C). In the present study, we tested the hypothesis that the noxious heat-evoked pain behavior that persists in TRPV1-mutant mice reflects residual responsiveness of neurons in the superficial, but not deep, dorsal horn. ⋯ We conclude that TRPV1 is necessary for noxious heat-evoked responses of lamina V neurons, both before and after tissue injury. It is also an essential contributor to the normal activation threshold of lamina I neurons to noxious heat and for the full duration of thermal sensitization of lamina I neurons following injury. Finally, our results suggest that the processing of noxious thermal messages by neurons in lamina I involves convergent inputs from a heterogeneous population of primary afferent thermal nociceptors.
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Inflammation, peripheral nerve injury and chemical irritants can cause central sensitization in pain pathways. Prostaglandins produced in the CNS induce central sensitization during inflammation mainly by relieving nociceptive neurons from glycinergic inhibition. We have recently identified spinal prostaglandin E receptors of the EP2 subtype (EP2 receptors) and the glycine receptor alpha3 subunit (GlyR alpha3) as signal transduction elements involved in the generation of central inflammatory hyperalgesia. ⋯ The lack of a phenotype in GlyR alpha3-/- mice together with the absence of a facilitating effect of intrathecal PGE2 on formalin-induced nociception in wild-type mice suggests that peripheral rather than spinal EP2 receptors are involved. These results indicate that inhibition of glycinergic neurotransmission by EP2 receptor activation does not contribute to pain following peripheral nerve injury or chemical irritation with formalin. Our results thus provide further evidence that inflammatory hyperalgesia and neuropathic pain involve different mechanisms of central sensitization.