Alterations in conduction characteristics of crushed peripheral nerves

Abstract

Purpose: Nerve crush injury results in the incapability to maintain conduction of an impulse. Disruption in the myelin sheath causes very important changes in the activities of ion channels. Therefore, crushed and intact sciatic nerves were researched with both histological and electrophysiological methods in this study.

Methods: Electron and light microscopy for histological examinations, a sucrose-gap recording techniques for electrophysiological examinations were used. 4-aminopyridine (4-AP) and Tetraethylammonium (TEA) were used to functional separation of the fast and slow K $^+$ channels.

Results: The number of damaged myelinated nerve fiber was counted as 750 ± 3.5. Lamellar separation and disruption in myelin sheath was frequently observed in these fibers. Conduction velocity of crushed nerves (19 ± 2 m/s) was half of the intact nerves. The relationship between equally spaced interstimulus interval and their responses demonstrated that 4-AP and 4-AP plus TEA have more pronounced effects on crushed nerves than on intact nerves. After 4-AP, TEA application caused an efficiently depolarization in the membrane potential.

Conclusions: The effects of 4-AP and 4-AP plus TEA suggest the involvement of slow and fast K $^+$ channels and slow Na $^+$ currents in membrane potential and action potential repolarization. Minimal myelin damage may significantly influence the subsequent impulse generation and the patterning of action potential activity.