Degeneration of myelinated efferent fibers induces spontaneous activity in uninjured C-fiber afferents

Gang Wu, Matthias Ringkamp, Beth B. Murinson, Esther M. Pogatzki, Timothy V. Hartke, Himali M. Weerahandi, James N. Campbell, John W. Griffin, Richard A. Meyer

Research output: Contribution to journalArticle

Abstract

We demonstrated recently that uninjured C-fiber nociceptors in the L4 spinal nerve develop spontaneous activity after transection of the L5 spinal nerve. We postulated that Wallerian degeneration leads to an alteration in the properties of the neighboring, uninjured afferents from adjacent spinal nerves. To explore the role of degeneration of myelinated versus unmyelinated fibers, we investigated the effects of an L5 ventral rhizotomy in rat. This lesion leads to degeneration predominantly in myelinated fibers. Mechanical paw-withdrawal thresholds were assessed with von Frey hairs, and teased-fiber techniques were used to record from single C-fiber afferents in the L4 spinal nerve. Behavioral and electrophysiological data were collected in a blinded manner. Seven days after surgery, a marked decrease in withdrawal thresholds was observed after the ventral rhizotomy but not after the sham operation. Single fiber recordings revealed low-frequency spontaneous activity in 25% of the C-fiber afferents 8-10 d after the lesion compared with only 11% after sham operation. Paw-withdrawal thresholds were inversely correlated with the incidence of spontaneous activity in high-threshold C-fiber afferents. In normal animals, low-frequency electrocutaneous stimulation at C-fiber, but not A-fiber, strength produced behavioral signs of secondary mechanical hyperalgesia on the paw. These results suggest that degeneration in myelinated efferent fibers is sufficient to induce spontaneous activity in C-fiber afferents and behavioral signs of mechanical hyperalgesia. Ectopic spontaneous activity from injured afferents was not required for the development of the neuropathic pain behavior. These results provide additional evidence for a role of Wallerian degeneration in neuropathic pain.

Original languageEnglish (US)
Pages (from-to)7746-7753
Number of pages8
JournalJournal of Neuroscience
Volume22
Issue number17
DOIs
StatePublished - Sep 1 2002

Keywords

  • Hyperalgesia
  • In vivo
  • Nerve injury
  • Neuropathic pain
  • Neuropathy
  • Sensitization
  • Single nerve fiber recording
  • Unmyelinated cutaneous afferent
  • Wallerian degeneration

ASJC Scopus subject areas

  • Neuroscience(all)

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