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Volume 17, Number 19,
Issue of October 1, 1997
pp. 7267-7277
Copyright ©1997 Society for Neuroscience
Conduction in Segmentally Demyelinated Mammalian Central
Axons
Received April 24, 1997; revised July 16, 1997; accepted July 18, 1997.
Paul A. Felts ,
Theresa A. Baker , and
Kenneth J. Smith
Department of Neurology, United Medical and Dental Schools of
Guy's and St. Thomas' Hospitals, Guy's Campus, London, SE1 9RT
United Kingdom
The prominent symptoms associated with central demyelinating
diseases such as multiple sclerosis (MS) are primarily caused by
conduction deficits in affected axons. The symptoms may go into
remission, but the mechanisms underlying remissions are uncertain. One
factor that could be important is the restoration of conduction to
affected axons, but it is not known whether demyelinated central axons
resemble their peripheral counterparts in being able to conduct in the
absence of repair by remyelination. In the present study we have made
intra-axonal recordings from central axons affected by a demyelinating
lesion, and then the axons have been labeled ionophoretically to permit
their subsequent identification. Ultrastructural examination of 23 labeled preparations has established that some segmentally demyelinated
central axons can conduct, and that they can do so over continuous
lengths of demyelination exceeding several internodes (2500 µm). Such
segmentally demyelinated central axons were found to conduct with the
anticipated reduction in velocity and a refractory period of
transmission (RPT) as much as 34 times the value obtained from the
nondemyelinated portion of the same axon; the RPT was typically
prolonged to 2-5 times the normal value. We conclude that some
segmentally demyelinated central axons can conduct, and we propose that
the restoration of conduction to such axons is likely to contribute to
the remissions commonly observed in diseases such as MS.
Key words:
demyelination;
multiple sclerosis;
axon;
conduction
properties;
glia;
ionophoresis
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