Journal of Neurophysiology, Vol 68, Issue 4 1160-1166, Copyright © 1992 by APS
Axonal cross-excitation in nerve-end neuromas: comparison of A- and C-fibers
R. Amir and M. Devor
Department of Cell and Animal Biology, Hebrew University of Jerusalem, Israel.
1. We recorded from single afferent axons ending in chronic sciatic nerve
end neuromas in rats with the use of the teased-fiber method. Axons were
sought that had ongoing impulse discharge originating in the neuroma. 2.
Recording from myelinated (A-) fibers, tetanic stimulation of neighboring
axons (50 Hz, 5 or 10 s, intensity adequate to drive A-fibers) caused an
increase, and sometimes a decrease, in the rate of ongoing discharge in 68%
of the fibers tested. In addition, some initially silent neuroma A-fibers
(1.4%) were activated in this way. Both A beta and A delta fibers
responded, although the likelihood of response was greater in A beta
fibers. We call this form of interfiber cross-excitation "crossed
afterdischarge." 3. In contrast to A-fibers, crossed afterdischarge was
evoked with these stimulation parameters in < or = 5% of the
spontaneously active unmyelinated (C-) fibers sampled. No initially silent
C-fibers were activated. 4. C-fibers remained largely insensitive to
cross-excitation by neighboring axons even when the strength of stimulus
pulses was increased so as to include neighboring A + C-fibers. 5. The
difference between A- and C-fibers could not be accounted for on the basis
of the maturity of the neuroma, rate and pattern of ongoing discharge, or
use of Flaxedil paralysis. 6. The difference between A- and C-fibers is
discussed in terms of two alternative mechanisms that may underlie crossed
afterdischarge: mediation by a neurotransmitter(s) in a nonsynaptic mode,
and mutual K+ depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
