Activity-dependent slowing of conduction velocity in uninjured L4 C fibers increases after an L5 spinal nerve injury in the rat

Beom Shim, Matthias Ringkamp, George L. Lambrinos, Timothy V. Hartke, John W. Griffin and Richard A. Meyer

Growing evidence suggests that uninjured afferents may play an important role in neuropathic pain following nerve injury. This study investigates whether the action-potential conduction properties of unlesioned, unmyelinated fibers are also altered. Blinded experiments were performed 8–10 days after sham surgery and after an L5 spinal nerve ligation. Activity-dependent slowing revealed two populations of C fibers, a “nociceptor” population with a large degree of activity-dependent slowing and a “non-nociceptor” population with a smaller degree of activity-dependent slowing. Both populations showed enhanced activity-dependent slowing of conduction velocity and enhanced supranormal conduction velocities in lesioned animals compared to sham animals. These alterations in conduction velocity may reflect changes in expression of ion channels responsible for the membrane excitability. These data provide additional evidence that a nerve injury leads to persistent alterations in the properties of adjacent uninjured, unmyelinated fibers.

Pain, Volume 128, Issues 1-2, March 2007, Pages 40-51

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