The Journal of Neuroscience, January 1, 1998, 18(1):328-338
Comparison of Neurite Outgrowth Induced by Intact and Injured
Sciatic Nerves: A Confocal and Functional Analysis
Eric
Agius and
Philippe
Cochard
Centre de Biologie du Développement, Centre National de la
Recherche Scientifique Unité Mixte de Recherche 5547, affiliée à l'Institut National de la Santé et de la
Recherche Médicale, Université Paul Sabatier, 31062 Toulouse, France
Mechanisms regulating axon growth in the peripheral nervous system
have been studied by means of an in vitro bioassay, the tissue section culture, in which regenerating neurons are grown on
substrata made up of tissue sections. Sections from intact and
degenerated sciatic nerves proved to be different in their ability to
support neurite outgrowth of embryonic chick sensory neurons from both
qualitative and quantitative points of view. On denervated nerve
sections, the total length of neurites elaborated per neuron was almost
twice that found on intact nerve sections. In addition, confocal
microscopy revealed a striking difference between intact and denervated
nerve substrata: on denervated nerve sections, neurites grew inside the
internal structures of endoneurial Schwann cell tubes, within the
underlying tissue sections, whereas on intact nerve sections neurites
extended along endoneurial basal laminae but never entered Schwann cell
tubes. Perturbation experiments were used to analyze some of the
molecular determinants that control neurite outgrowth in this system.
Antibodies directed against the 
1-integrin subunit inhibited neurite
extension on both normal and degenerated rat sciatic nerve tissue.
Strikingly, however, differential inhibition was observed using
antibodies directed against extracellular matrix molecules.
Anti-laminin-2 (merosin) antibodies drastically reduced both the
percentage of growing neurons and the total length of neurites on
denervated nerve sections, but they did not modify these parameters on
sections of normal nerve. Taken together, these results suggest that
laminin-2/merosin promotes neurite outgrowth in peripheral nerve
environments but only after Wallerian degeneration, which is when axons
are allowed to extend within endoneurial tubes.
Key words:
nerve fiber growth; axon regeneration; peripheral nervous
system; Wallerian degeneration; rat sciatic nerve; extracellular
matrix; integrin; merosin; cryoculture; bioassay; confocal
microscopy
Copyright © 1998 Society for Neuroscience 0270-6474/98/181328-11$05.00/0
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