The Journal of Cell Biology, Vol 87, 197-203, Copyright © 1980 by The Rockefeller University Press
Axonal growth during regeneration: a quantitative autoradiographic study
A Tessler, A Autilio-Gambetti and P Gambetti
The intraaxonal distribution of labeled glycoproteins in the regenerating
hypoglossal nerve of the rabbit was studied by use of quantitative electron
microscope autoradiography. 9 d after nerve crush, glycoproteins were
labeled by the administration of [3H]fucose to the medulla. The
distribution of transported 3H-labeled glycoproteins was determined 18 h
later in segments of the regenerating nerve and in the contralateral,
intact nerve. At the regenerating tip, the distribution was determined both
in growth cones and in non-growth cone axons, 6 and 18 h after labeling.
The distribution within the non- growth cone axons of the tips was quite
different at 6 and 18 h. At 6 h, the axolemma region contained < 10% of
the radioactivity; at 18 h, it contained virtually all the radioactivity.
In contrast, the distribution within the growth cones was similar at both
time intervals, with 30% of the radioactivity over the axolemmal region.
Additional segments of the regenerating nerve also showed a preferential
labeling of the axolemmal region. In the intact nerve, 3H- labeled
glycoproteins were uniformly distributed. These results suggest that: (a)
in this system the labeled glycoproteins reaching the tip of the
regenerating axons are inserted into the axolemma between 6 and 18 h after
leaving the neuronal perikaryon; (b) at the times studied, there is a
fairly constant ratio between glycoproteins reaching the growth cone
through axoplasmic transport and glycoproteins inserted into the growth
cone axolemma; (c) the axolemma elongates by continuous insertion of
membrane precursors at the growth cone; the growth cone then advances,
leaving behind an immature axon with a newly formed axolemma; and (d)
glycoproteins are preferentially inserted into the axolemma along the
entire regenerating axon.
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