Pain
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There is evidence that inflammatory processes are involved in at least the early phase of complex regional pain syndrome (CRPS). We compared a panel of pro- and antiinflammatory cytokines in skin blister fluids and serum from patients with CRPS and patients with upper-limb pain of other origin (non-CRPS) in the early stage (< 1 year) and after 6 months of pain treatment. Blister fluid was collected from the affected and contralateral nonaffected side. ⋯ Blister fluid of CRPS patients showed a bilateral proinflammatory cytokine profile. This profile seems to be relevant only at the early stage of CRPS. Almost all measured cytokine levels were comparable to those of non-CRPS patients after 6 months of analgesic treatment and were not related to treatment outcome.
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Stressful experiences seem to negatively influence pain perception through as yet unknown mechanisms. As the noradrenergic locus coeruleus (LC) nucleus coordinates many components of the stress response, as well as nociceptive transmission, we evaluated whether the sensory and affective dimension of chronic neuropathic pain worsens in situations of stress due to adaptive changes of LC neurons. Accordingly, male rats were socially isolated for 5 weeks, and in the last 2 weeks, neuropathic pain was induced by chronic constriction injury. ⋯ These changes were accompanied by an increase in tyrosine hydroxylase and gephyrin expression in the LC. Furthermore, intra-LC administration of bicuculline, a γ-aminobutyric acid-A receptor antagonist, attenuated the negative affective effects of pain. These data show that changes in the LC are greater than those expected from the simple summation of each independent factor (pain and stress), revealing mechanisms through which stressors may exacerbate pain perception without affecting the sensorial dimension.