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This Article Full Text Full Text (PDF) All Versions of this Article: 101/6/2762    most recent 91091.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Grossmann, L. Articles by Jänig, W. PubMed PubMed Citation Articles by Grossmann, L. Articles by Jänig, W.

Enhancement of Ectopic Discharge in Regenerating A- and C-Fibers by Inflammatory Mediators

¹Physiologisches Institut and ²Division of Neurological Pain Research and Therapy, Department of Neurology, Christian-Albrechts-Universität zu Kiel, Kiel, Germany

Submitted 18 September 2008; accepted in final form 5 March 2009

Afferent A- and C-fibers regenerating into a nerve following peripheral nerve injury are exposed to inflammatory mediators released by Schwann cells, resident and invading macrophages, and other inflammatory cells. Here we tested the hypothesis that ongoing and evoked activity in these afferent fibers are enhanced by a mixture of inflammatory mediators [inflammatory soup (IS)] applied to the injured nerve. Using in vivo electrophysiology, regenerating afferent nerve fibers were studied 7–14 days after sural nerve crush lesion. The ectopic activity was studied before and 1.5 h after topical application of IS to the nerve in 73 C-fibers and 22 A-fibers that were either ectopically active before application of IS (61 C-fibers, 17 A-fibers) or recruited by IS (12 C-fibers, 5 A-fibers). More than one half of the C-fibers were activated by IS for 90 min after its removal. The majority of mechano- (23/38) and heat-sensitive (29/35) C-fibers as well as mechano-sensitive A-fibers (12/17) decreased their activation thresholds and/or increased the response magnitude to mechanical and/or heat stimulation of the nerve. Noxious cold sensitivity, but not nonnoxious cold sensitivity, was weakly influenced by IS. Some initially nonresponsive C- and A-fibers developed new ectopic properties, i.e., were recruited, and exhibited ongoing activity and/or could be activated by physiological stimuli after application of IS. The results suggest that inflammatory mediators may be critical to enhance ectopic excitability of regenerating afferent nerve fibers. These peripheral mechanisms may be important triggering and maintaining neuropathic pain.