| 1. |
- Jörum, E., et al.
(författare)
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Catecholamine-induced excitation of nociceptors in sympathetically maintained pain
- 2007
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Ingår i: Pain. - : Ovid Technologies (Wolters Kluwer Health). - 0304-3959 .- 1872-6623. ; 127:3, s. 296-301
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Tidskriftsartikel (refereegranskat)abstract
- Sympathetically maintained pain could either be mediated by ephaptic interactions between sympathetic efferent and afferent nociceptive fibers or by catecholamine-induced activation of nociceptive nerve endings. We report here single fiber recordings from C nociceptors in a patient with sympathetically maintained pain, in whom sympathetic blockade had repeatedly eliminated the ongoing pain in both legs. We classified eight C-fibers as mechano-responsive and six as mechano-insensitive nociceptors according to their mechanical responsiveness and activity-dependent slowing of conduction velocity (latency increase of 0.5±1.1 vs. 7.1±2.0ms for 20 pulses at 0.125Hz). Two C-fibers were activated with a delay of several seconds following strong endogenous sympathetic bursts; they were also excited for about 3min following the injection of norepinephrine (10μl, 0.05%) into their innervation territory. In these two fibers, a prolonged activation by injection of low pH solution (phosphate buffer, pH 6.0, 10μl) and sensitization of their heat response following prostaglandin E2 injection were recorded, evidencing their afferent nature. Moreover, their activity-dependent slowing was typical for mechano-insensitive nociceptors. We conclude that sensitized mechano-insensitive nociceptors can be activated by endogenously released catecholamines and thereby may contribute to sympathetically maintained pain. No evidence for ephaptic interaction between sympathetic efferent and nociceptive afferent fibers was found.
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| 2. |
- Namer, B., et al.
(författare)
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Microneurographic assessment of C-fibre function in aged healthy subjects
- 2009
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 587:Pt 2, s. 419-428
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Tidskriftsartikel (refereegranskat)abstract
- Physiological changes in the nervous system occur with ageing. Both a decline of function and a decrease in the number of C-fibres in the skin have been reported for healthy aged subjects. With the use of microneurographic recordings from single C-fibres in humans we have compared the sensory and axonal properties of these neurones in young and aged healthy subjects. A total of 146 C-fibres were recorded from the common peroneal nerve in young subjects (mean age 24.7 years) and 230 C-fibres were recorded in aged subjects (mean age 56.2 years). In aged subjects, changes were found in the composition of the C-fibre population and in sensory and axonal properties. The relative incidence of afferent to efferent C-fibres was relatively constant independent of the age of subjects. The ratio of mechano-responsive to mechano-insensitive nociceptors was approximately 8 : 2 in the young controls while in aged subjects it was 7 : 3. In aged subjects 13% of the fibres showed atypical discharge characteristics, while this was not observed in young subjects. Spontaneous activity, sensitization and loss of sensory function were found regularly. Changes in functions of the conductile membrane were also observed in fibres from aged subjects. The degree of activity-dependent conduction velocity slowing in response to high frequency stimulation (2 Hz) was more pronounced, while the normalization of conduction velocity subsequent to high frequency stimulation was protracted. We found that both sensitization and desensitization or degeneration of afferent C-fibres occur with age, but are still rare compared to patients with neuropathy. The changes in the axonal properties of C-fibres in aged subjects are compatible with hypoexcitability of the fibres. These findings are important for the understanding and differential diagnoses regarding pathological processes and normal ageing.
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| 3. |
- Schmelz, M., et al.
(författare)
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Active "itch fibers" in chronic pruritus
- 2003
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Ingår i: Neurology. - : Lippincott Williams & Wilkins. - 0028-3878 .- 1526-632X. ; 61:4, s. 564-566
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Tidskriftsartikel (refereegranskat)abstract
- An itch-specific neuronal pathway was recently discovered in healthy humans and animals. Here the authors report that activity in this specific pathway coincides with itch under pathophysiologic conditions in a patient with chronic pruritus. Microneurographic recordings from the symptomatic area revealed spontaneous activity in six single C-fiber afferents that had the characteristic features of "itch fibers." Itch may be caused by activity in a specific subpopulation of C-fiber afferents.
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| 4. |
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| 5. |
- Örstavik, K., et al.
(författare)
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Abnormal function of C-fibers in patients with diabetic neuropathy
- 2006
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Ingår i: Journal of Neuroscience. - Washington DC, USA : The Society for Neuroscience. - 0270-6474 .- 1529-2401. ; 26:44, s. 11287-11294
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms underlying the development of painful and nonpainful neuropathy associated with diabetes mellitus are unclear. We have obtained microneurographic recordings from unmyelinated fibers in eight patients with diabetes mellitus, five with painful neuropathy, and three with neuropathy without pain. All eight patients had large-fiber neuropathy, and seven patients had pathological thermal thresholds in their feet, indicating the involvement of small-caliber nerve fibers. A total of 163 C-fibers were recorded at knee level from the common peroneal nerve in the patients (36-67 years old), and these were compared with 77 C-fibers from healthy controls (41-64 years old). The ratio of mechano-responsive to mechano-insensitive nociceptors was similar to 2:1 in the healthy controls, whereas in the patients, it was 1:2. In patients, a fairly large percentage of characterized fibers (12.5% in nonpainful and 18.9% in painful neuropathy) resembled mechano-responsive nociceptors that had lost their mechanical and heat responsiveness. Such fibers were rarely encountered in age-matched controls (3.2%). Afferent fibers with spontaneous activity or mechanical sensitization were found in both patient groups. We conclude that small-fiber neuropathy in diabetes affects receptive properties of nociceptors that leads to an impairment of mechano-responsive nociceptors.
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