Reductions in motoneuronal neurofilament synthesis by successive axotomies: a possible explanation for the conditioning lesion effect on axon regeneration.
Axons regenerate more rapidly after a test lesion if they received a conditioning lesion. Previous work suggests that the cell body reaction to injury is responsible for this conditioning lesion effect. Here we examined the effects of the second, test lesion on the expression of the major cytoskeletal proteins, tubulin, actin, and neurofilament proteins. Using 2D-SDS-PAGE to separate these cytoskeletal proteins synthesized in the facial nucleus, along with in situ hybridization and RNA blotting to measure corresponding mRNA levels, we found that previous conditioning had little effect on actin or tubulin responses to a test lesion, but resulted in further decrease in neurofilament synthesis. Immunocytochemistry and electron microscopy revealed a greater loss of neurofilaments from the proximal conditioned axons, and axonal shrinkage. We suggest that the reduction in neurofilaments in the proximal axons of conditioned neurons reduces interference with tubulin transport. This may allow more tubulin to be transported more rapidly into the growing axon, to support the faster elongation rate of conditioned axons following a test lesion.
Tetzlaff
W
W
Department of Physiology, University of Ottawa, Ontario, Canada.
Leonard
C
C
Krekoski
C A
CA
Parhad
I M
IM
Bisby
M A
MA
D000818:Animals; D001369:Axons / Q000502:physiology*; D003599:Cytoskeleton / Q000737:chemistry / Q000235:genetics; D003714:Denervation; D005154:Facial Nerve / Q000166:cytology / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D008715:Methionine / Q000378:metabolism; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009416:Nerve Regeneration / Q000502:physiology*; D016900:Neurofilament Proteins / Q000032:analysis / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013462:Sulfur Radioisotopes / Q000378:metabolism
D016900:Neurofilament Proteins; D012333:RNA, Messenger; D013462:Sulfur Radioisotopes; D008715:Methionine