Pain
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Pain and frailty are both prevalent and have severe health impacts among older adults. We conducted a cross-sectional observational study to examine the association between pain and frailty, and depression as a mediator and its interaction with pain on frailty among 1788 Chinese community-dwelling older adults. Physical frailty, pain intensity, and depressive symptoms were assessed using the Frailty Phenotype, the Faces Pain Scale-revised, and the 5-item Geriatric Depression Scale, respectively. ⋯ The relative excess risk of interaction, the attributable proportion due to interaction, and the synergy index (S) were 4.08, 0.50, and 2.34, respectively. These findings suggest that the positive association of pain with frailty is persistent and partially mediated by depression, and comorbid depression and pain have an additive interaction on physical frailty. It has an implication of multidisciplinary care for frail older adults with pain.
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Issues of peripheral circulation have been increasingly suggested as an underlying cause of musculoskeletal pain in many conditions, including sickle cell anemia and peripheral vascular disease. We have previously shown in our model of transient ischemia and reperfusion (I/R) injury of the forelimb that individual group III and IV muscle afferents display altered chemosensitivity and mechanical thresholds 1 day after injury. Functional alterations corresponded to increased evoked and spontaneous pain-related behaviors and decreased muscle strength and voluntary activity-all actions that echo clinical symptoms of ischemic myalgia. ⋯ Interleukin 1 receptor antagonist treatment additionally prevented the I/R-induced changes in mechanical and chemical sensitivity of individual primary muscle afferents. Altogether, these data strengthen the evidence that transient I/R injury sensitizes group III and IV muscle afferents via increased IL1β in the muscles to stimulate ischemic myalgia development. Targeting IL1β may, therefore, be an effective treatment strategy for this insidious type of muscle pain.
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The exteroceptive sensory system is responsible for sensing external stimuli in relation to time and space. The aim of this study was to investigate the tempo-spatial properties of the exteroceptive system using painful laser heat and nonpainful mechanical touch stimulation. Thirteen healthy subjects were stimulated on the volar forearm using 2 paradigms: a continuous stimulation along a line on the skin and a 2-point stimulation. ⋯ Numeric rating scale increased both with line length and distance between the 2 points (linear mixed model, P < 0.001). The findings indicate that the tempo-spatial acuity of the exteroceptive system is lower for noxious stimuli than for innocuous stimuli. This is possible due to the larger receptive fields of nociceptive neurons and/or less lateral inhibition.
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Pain sensitization after partial infraorbital nerve transection (p-IONX) in mice not only presents in orofacial region, but also spreads to distant body parts. The roles of toll-like receptor 4 (TLR4) in orofacial pain and the spreading process are still unclear. Here, we found that mice with deficient TLR4 because of Tr4 gene point mutation (C3H/HeJ) or spontaneous deletion (C57BL/10ScNJ) developed tactile allodynia and thermal hyperalgesia in the vibrissal pad in a parallel way to their respective wild types (C3HeB/FeJ or C57BL/6J) after p-IONX. ⋯ The hypersensitivity, which did not spread to the vibrissal pad, was accompanied with upregulation of MyD88 in the lumbar cord rather than in the medulla. These results suggest that TLR4 participates in the spread of allodynia component of orofacial pain to distant body sites, but not trigeminal neuropathic pain or the spread of its hyperalgesia component. This study suggests that TLR4 may serve as a potential target for the management of widespread allodynia associated with orofacial pain.