Axonal transport and localization of B-50/GAP-43-like immunoreactivity in regenerating sciatic and facial nerves of the rat.
Neurons that can regenerate their axons following axotomy increase their synthesis and axonal transport of a growth-associated protein, called GAP-43, which has been shown to be identical to the synaptic phosphoprotein B-50. The function of B-50/GAP-43 to the process of regeneration is unknown. We used a polyclonal, affinity-purified antibody against B-50 to study the axonal transport and localization of B-50/GAP-43-like immunoreactivity (B50LI) in the regenerating sciatic and facial nerves of adult rats. Quantitative data were obtained by densitometry of the B-50 band in immunoblots of nerve segments, which had been run on SDS-polyacrylamide gels. In the regenerating sciatic nerve, anterograde accumulation at a collection ligature was 3.0 times higher than retrograde accumulation. The mobile fraction of B50LI was only 0.28 of total B50LI and traveled with a mean anterograde velocity of 5.3 mm/hr. B50LI distribution in the newly regenerated portion of the nerve revealed maximal B50LI levels midway between the position of the crush and the fastest-growing axons. Immunocytochemistry of this portion of the nerve demonstrated B50LI to be associated with regenerating axons but also to a large extent with extra-axonal structures outlining the Schwann cell bands of Büngner. This zone of B50LI-positive Schwann cell bands was found to extend more distally in nerves in which regeneration had processed longer, e.g., up to 5 mm distal to the crush after 3 d and 8 mm after 4 d. Further distal to this zone, many fine regenerating axonal profiles could be detected with B-50 antibody, but were neurofilament negative. These findings raise the possibility of an extra-axonal function of B-50/GAP-43, as this protein might be secreted from regenerating axons and might play a role in axon-Schwann cell interactions during axonal maturation.
Tetzlaff
W
W
Department of Medical Physiology, University of Calgary, Alberta, Canada.
Zwiers
H
H
Lederis
K
K
Cassar
L
L
Bisby
M A
MA
D000818:Animals; D001369:Axons / Q000378:metabolism*; D001692:Biological Transport; D005154:Facial Nerve / Q000378:metabolism / Q000502:physiology*; D019922:GAP-43 Protein; D007150:Immunohistochemistry; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009416:Nerve Regeneration; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012584:Sciatic Nerve / Q000378:metabolism / Q000502:physiology*; D014018:Tissue Distribution
D019922:GAP-43 Protein; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins