Pain
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A vast diversity of salient cues is sensed by numerous classes of primary sensory neurons, defined by specific neuropeptides, ion channels, or cytoskeletal proteins. Recent evidence has demonstrated a correlation between the expression of some of these molecular markers and transmission of signals related to distinct sensory modalities (eg, heat, cold, pressure). Voltage-gated sodium channel Na(v)1.8 has been reported to be preferentially expressed in small-diameter unmyelinated sensory afferents specialized for the detection of noxious stimuli (nociceptors), and Na(v)1.8-Cre mice have been widely used to investigate gene function in nociceptors. ⋯ We demonstrate that 75% of dorsal root ganglion (DRG) neurons express Na(v)1.8-Cre, including >90% of neurons expressing markers of nociceptors and, unexpectedly, a large population (∼40%) of neurons with myelinated A fibers. Furthermore, analysis of DRG neurons' central and peripheral projections revealed that Na(v)1.8-Cre is not restricted to nociceptors but is also expressed by at least 2 types of low-threshold mechanoreceptors essential for touch sensation, including those with C and Aβ fibers. Our results indicate that Na(v)1.8 underlies electrical activity of sensory neurons subserving multiple functional modalities, and call for cautious interpretation of the phenotypes of Na(v)1.8-Cre-driven conditional knockout mice.
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In this clinical and neurophysiological study, we examined the clinical characteristics and underlying mechanisms of neuropathic pain related to multiple sclerosis. A total of 302 consecutive patients with multiple sclerosis were screened for neuropathic pain by clinical examination and the DN4 tool. In patients selected for having ongoing extremity pain or Lhermitte's phenomenon, we recorded somatosensory evoked potentials, mediated by Aβ non-nociceptive fibres, and laser evoked potentials, mediated by Aδ nociceptive fibres. ⋯ The prevalence of pain that we found, which was lower than that reported in previous studies, may reflect the lesser disease severity in our patients. Neurophysiological data show that whereas ongoing extremity pain is associated with spinothalamic pathway damage, Lhermitte's phenomenon is related to damage of non-nociceptive pathways. These findings may be useful in designing a new therapeutic approach to neuropathic pain related to multiple sclerosis.
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Headache is a common health complaint responsible for substantial suffering and disability. Although musculoskeletal complaints such as back and neck pain have frequently been associated with occupational psychological and social factors, headache has received less attention as a possible outcome of such exposures. The aim of the present study was to identify occupational psychological, social, and mechanical factors that predicted headache severity. ⋯ Reverse effects from headache severity to quantitative demands were indicated. For role conflict, no cross-lagged effects were observed. However, synchronous models supported the notion of an effect of each of these factors on headache severity over a time span shorter than 2 years.
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A recent cross-sectional study of National Guard troops found that pain and pain catastrophizing were prevalent and highly correlated with posttraumatic stress disorder (PTSD). At issue in the present study was whether pain and catastrophizing before military deployment could account for individual differences in PTSD symptoms after deployment. An anonymous survey was administered to a population sample of New Jersey National Guard troops before they were sent overseas and again when they returned home (1 year later). ⋯ Consistent with previous research, a cross-sectional analysis revealed that postdeployment pain and catastrophizing successfully accounted for unique variance in postdeployment PTSD. The failure of longitudinal predictors in the present study, therefore, cannot be attributed to insensitive screening instruments. These findings offer little or no support for the hypothesis that predeployment pain and catastrophizing can account for individual differences in PTSD after exposure to combat trauma.
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Pain stimuli evoke widespread responses in the brain. However, our understanding of the physiological significance underlying heterogeneous response within different pain-activated and -deactivated regions is still limited. Using functional magnetic resonance imaging, we evaluated brain responses to a wide range of stimulus intensity levels (1 innocuous, 7 painful) in order to estimate region-specific stimulus-response functions, which we hypothesized could illuminate that region's functional relationship to pain. ⋯ Multiple activity profiles were seen in areas of the default mode network (DMN): intensity-independent deactivation (eg, posterior cingulate cortex), linearly decreasing (eg, contralateral inferior parietal lobule), and quadratic (U-shaped; eg, medial prefrontal cortex). The latter observation suggests that: (1) different DMN subregions exhibit functional heterogeneity and (2) some DMN subregions respond in a percept-related manner to pain, suggesting closer linkage between the DMN and pain processing than previously thought. Future studies should apply a similar approach using innocuous stimuli of multiple intensities to evaluate whether the response profiles reported here can also be generalized to nonpainful somatosensory processing.