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The Journal of Neuroscience, November 15, 1998, 18(22):9376-9385
Schwann Cells Proliferate at Rat Neuromuscular Junctions during
Development and Regeneration
Flora M.
Love and
Wesley J.
Thompson
Department of Zoology, University of Texas at Austin, Austin, Texas
78712
Terminal Schwann cells (TSCs) cover neuromuscular junctions and are
important in the repair and maintenance of these synapses. We have
examined how these cells are generated at developing junctions and how
their number is regulated during repair of nerve injury. At birth,
approximately half of the junctions in rat soleus and extensor
digitorum longus muscles have one TSC soma. Somata are absent from the
remainder, although Schwann cell (SC) processes arising from somata
along the preterminal axon cover almost all of these synapses. By 2 months of age, junctions have gained an additional two to three TSCs.
Most of this gain occurs during the first 2 postnatal weeks and largely
precedes the expansion of endplate size. Although the initial addition
is caused by cell migration, mitotic labeling shows extensive division
of TSCs at junctions. A slower addition of TSCs occurs in adult
muscles, and TSC number in the adult is correlated with endplate size.
During repair of nerve injury, TSC number is regulated by a combination
of signals from motor neurons and denervated tissue. As shown
previously (), denervation of adult muscles did not,
in itself, cause TSC mitosis. However, TSCs became mitotic during
reinnervation. Partial denervation induced division of TSCs at
innervated but not denervated endplates. A disproportionate number of
these mitotic cells were found at endplates contacted by TSC processes
extended from nearby denervated endplates, contacts known to promote
nerve sprouting. These results show an association between TSC mitotic
activity and alterations in synaptic structure during development,
sprouting, and reinnervation.
Key words:
Schwann cell; proliferation; mitosis; migration; cell
number; neuromuscular junction; development; partial denervation; reinnervation; denervation; sprouting; endplate area
Copyright © 1998 Society for Neuroscience 0270-6474/98/18229376-10$05.00/0
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