Pain
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Spatial summation (SS) and spatial discrimination (SD) are essential for pain perception. In the cold-pain sensation, these processes have hardly been studied. Our aim was to study the SS and SD of cold pain, as well as the SS of cold-pain threshold (CPT) in hairy and glabrous skin. ⋯ CPT was significantly higher in hairy than glabrous skin, but the amount of SS of CPT was similar in the 2 skin types. Noxious cold-evoked thermal qualities were more common in the glabrous than the hairy skin. In conclusion: (1) SS and SD of cold pain are reciprocal; (2) whereas cold pain can summate over large distances, the SD of cold pain is poor; (3) SS of cold pain does not exist between contralateral body sides, however, inhibition occurs; (4) SS is independent of skin type and sensitivity to cold pain; (5) differences in pain quality between hairy and glabrous skin may reflect innervation differences.
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We have proposed that neuropathic pain engages emotional learning, suggesting the involvement of the hippocampus. Because cytokines in the periphery contribute to induction and maintenance of neuropathic pain but might also participate centrally, we used 2 neuropathic pain models, chronic constriction injury (CCI) and spared nerve injury (SNI), to investigate the temporal profile of hippocampal cytokine gene expression in 2 rat strains that show different postinjury behavioral threshold sensitivities. SNI induced long-lasting allodynia in both strains, while CCI induced allodynia with time-dependent recovery in Sprague Dawley (SD) and no allodynia in Wistar Kyoto (WK) rats. ⋯ Conversely, in SD rats, SNI resulted in sustained and robust increased hippocampal IL-1β expression, which was only transient in rats with CCI. In this strain, IL-6 expression was not affected in any of the 2 injury models and IL-1ra expression was significantly increased in rats with SNI or CCI at late phases. We found that the degree and development of neuropathic pain depend on the specific nerve injury model and rat strain; that hippocampal IL-1β mRNA levels correlate with neuropathic pain behavior; that, in contrast to sham-operated animals, there are no correlations between hippocampal IL-1β and IL-1ra or IL-6 in neuropathic rats; and that alterations in cytokine expression are restricted to the hippocampus contralateral to the injury side, again implying that the observed changes reflect nociception.
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Multicenter Study
The mediating role of pain in substance use and depressive symptoms among Multicenter AIDS Cohort Study (MACS) participants.
Pain in human immunodeficiency virus (HIV) frequently co-occurs with substance use and depression. The complex associations among patient characteristics, pain, depression, and drug use in HIV suggests a role for testing models that can account for relationships simultaneously, control for HIV status, and also test for mediation. Using structural equation modeling, the current study examined associations among pain, sociodemographics, illicit drug use, and depressive symptoms in 921 HIV-seropositive and 1019 HIV-seronegative men from the Multicenter AIDS Cohort Study, an ongoing prospective study of the natural history of HIV infection among gay/bisexual men. ⋯ HIV-seropositive status predicted more use of inhaled nitrites. In this cohort, having lower CD4+ cell counts (predicted by HIV status), being African American, less educated, and older were all associated with more pain, which, in turn, was associated with more illicit drug use and more depressive symptoms. The results underscore the need for adequate pain management, particularly among vulnerable subgroups of HIV-seropositive and HIV-seronegative men to reduce the risk of drug use and depression.
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Randomized Controlled Trial Comparative Study
TRP-channel-specific cutaneous eicosanoid release patterns.
Analyzing mechanisms and key players in peripheral nociception nonneuronal skin cells are getting more and more into focus. Herein we investigated the functional expression of TRPV1 and TRPA1 in human keratinocytes and fibroblasts and assessed proinflammatory lipid mediator release upon their stimulation as well as sensory effects after topical application, combining in vitro and in vivo approaches. In vitro, the expression of functional TRPV1 and TRPA1 channels on fibroblasts and keratinocytes was confirmed via immunofluorescence, qualitative real time (RT) polymerase chain reaction, and cellular Ca(2+) influx measurements. ⋯ In parallel, heat pain thresholds were reduced by both agents after short-term topical application, but only AITC provoked a long-lasting local erythema. In conclusion, the agonist-induced activation of nociceptors by TRPA1 and TRPV1 elicits painful sensations, whereas nonneuronal tissue cells respond with differential release of inflammatory mediators, thus influencing local vasodilatation and neuronal sensitization. These results have implications for the application of transient receptor potential antagonists to improve inflammatory skin conditions and pain management.