Electrophysiology and morphometry of the Aα- and Aβ-fiber populations in the normal and regenerating rat sciatic nerve

• Published in: Experimental neurology 2004-06, Vol.187 (2), p.337-349
• Main Authors: Vleggeert-Lankamp, Carmen L.A.M., van den Berg, Rutgeris J., Feirabend, Hans K.P., Lakke, Egbert A.J.F., Malessy, Martijn J.A., Thomeer, Ralph T.W.M.
• Format: Article
• Language: English
• Subjects: Aα- and Aβ-fibers; Biological and medical sciences; Cranial nerves. Peripheral nerves. Autonomic nervous system; Electrophysiology; Injuries of the nervous system and the skull. Diseases due to physical agents; Medical sciences; Morphometry; Nerve graft; Neurosurgery; Regeneration; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Transplant; Traumas. Diseases due to physical agents
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2004.01.019

We studied electrophysiological and morphological properties of the Aα- and Aβ-fibers in the regenerating sciatic nerve to establish whether these fiber types regenerate in numerical proportion and whether and how the electrophysiological properties of these fiber types are adjusted during regeneration. Compound action potentials were evoked from isolated sciatic nerves 12 weeks after autografting. Nerve fibers were gradually recruited either by increasing the stimulus voltage from subthreshold to supramaximal levels or by increasing the interval between two supramaximal stimuli to obtain the cumulative distribution of the extracellular firing thresholds and refractory periods, respectively. Thus, the mean conduction velocity (MCV), the maximal charge displaced during the compound action potential ( Q max), the mean firing threshold ( V 50), and the mean refractory period ( t 50) were determined. The number of myelinated nerve fibers and their fiber diameter frequency distributions were determined in the peroneal nerve. Mathematical modeling applied to fiber recruitment and diameter distributions allowed discrimination of the Aα- and Aβ-fiber populations. In regenerating nerves, the number of Aα-fibers increased fourfold while the number of Aβ-fibers did not change. In regenerating Aα- and Aβ-fibers, the fiber diameter decreased and V 50 and t 50 increased. The regenerating Aα-fibers' contribution to Q max decreased considerably while that of the Aβ-fibers remained the same. Correlation of the electrophysiological data to the morphological data provided indications that the ion channel composition of both the Aα- and Aβ-fibers are altered during regeneration. This demonstrates that combining morphometric and electrophysiological analysis provides better insight in the changes that occur during regeneration.