Fiber composition of the rat sciatic nerve and its modification during regeneration through a sieve electrode.
Recovery after peripheral nerve transection is seldom complete, the outcome depending both on lesion and repair conditions, and on the type and neurochemical properties of axons. The interposition between the stumps of a perforated, or regenerative electrode (RE) is a promising avenue in the use of chronic nerve bioimplants, but represents an additional challenge to regeneration. We applied stereological methods to ultrathin and immunostained semithin sections to examine quantitatively the axon types that make up the sciatic nerve in control adult rats, and their changes 2 months after an RE implant. The number of myelinated axons (MAx) increased proximal to RE, but fell to 10% a few millimeters distal. This decrease affected more severely motor fibers, characterized by immunoreactivity to cholinacetyltransferase (ChAT+), than sensory (ChAT-) fibers. Regenerating MAx and myelin sheaths also changed notably in thickness. Unmyelinated axons (UAx) showed a moderate reduction in number distal to the implant. This reduction affected more tyrosine hydroxylase-immunoreactive axons (mostly vaso- and pilomotor fibers), than axons expressing ChAT and/or vasoactive intestinal peptide (mostly sudomotor fibers). Taken together with previous findings [Negredo, P., Castro, J., Lago, N., Navarro, X., Avendaño, C., 2004. Differential growth of axons from sensory and motor neurons through a regenerative electrode: a stereological, retrograde tracer, and functional study in the rat. Neuroscience 128, 605-615.], this study shows that regeneration through the RE is much less successful for MAx than UAx, that motor axons regenerate more poorly than sensory axons, and that some subclasses of sympathetic fibers regenerate better than others. The study also proves the value of the combined methodological approach presented here to assess the fiber composition of a nerve under normal, pathological or experimental conditions.
Castro
Jorge
J
Department of Anatomy, Histology and Neuroscience, Autonoma University, Medical School, Madrid, Spain.
Negredo
Pilar
P
Avendaño
Carlos
C
D000818:Animals; D001369:Axons / Q000145:classification / Q000378:metabolism / Q000648:ultrastructure; D001705:Bioprosthesis; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D004599:Electric Stimulation Therapy / Q000295:instrumentation; D004567:Electrodes, Implanted; D004594:Electrophysiology / Q000295:instrumentation; D005260:Female; D048091:Guided Tissue Regeneration / Q000379:methods*; D008297:Male; D008839:Microelectrodes; D009046:Motor Neurons / Q000378:metabolism / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000145:classification / Q000378:metabolism / Q000648:ultrastructure*; D036421:Nerve Fibers, Unmyelinated / Q000145:classification / Q000378:metabolism / Q000648:ultrastructure*; D009416:Nerve Regeneration / Q000502:physiology*; D009475:Neurons, Afferent / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D020127:Recovery of Function / Q000502:physiology; D012584:Sciatic Nerve / Q000293:injuries / Q000378:metabolism / Q000648:ultrastructure*; D020426:Sciatic Neuropathy / Q000378:metabolism / Q000473:pathology*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
D014660:Vasoactive Intestinal Peptide; D002795:Choline O-Acetyltransferase