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The Journal of Neurophysiology Vol. 85 No. 2 February 2001, pp. 644-658
Copyright ©2001 by the American Physiological Society
1Department of Pharmacology and Division of Neuroscience, University of Alberta, Edmonton, Alberta T6G 2H7, Canada; and 2Department of Physical Therapy, Tennessee State University, Nashville, Tennessee 37209
Abdulla, Fuad A. and
Peter A. Smith.
Axotomy- and Autotomy-Induced Changes in Ca2+and
K+ Channel Currents of Rat Dorsal Root Ganglion Neurons. J. Neurophysiol. 85: 644-658, 2001. Sciatic nerve section (axotomy) increases the
excitability of rat dorsal root ganglion (DRG) neurons. The changes in
Ca2+ currents, K+ currents,
Ca2+-sensitive K+ current,
and hyperpolarization-activated cation current
(IH) that may be associated with this
effect were examined by whole cell recording. Axotomy affected the same
conductances in all types of DRG neuron. In general, the largest
changes were seen in "small" cells and the smallest changes were
seen in "large" cells. High-voltage-activated
Ca2+-channel current
(HVA-IBa) was reduced by axotomy.
Although currents recorded in axotomized neurons exhibited increased
inactivation, this did not account for all of the reduction
in HVA-IBa. Activation kinetics were
unchanged, and experiments with nifedipine and/or
-conotoxin GVIA
showed that there was no change in the percentage contribution of
L-type, N-type, or "other" HVA-IBa
to the total current after axotomy. T-type (low-voltage-activated)
IBa was not affected by axotomy.
Ca2+-sensitive K+
conductance (gK,Ca) appeared to be
reduced, but when voltage protocols were adjusted to elicit similar
amounts of Ca2+ influx into control and
axotomized cells, IK,Ca(s) were
unchanged. After axotomy, Cd2+-insensitive,
steady-state K+ channel current, which primarily
comprised delayed rectifier K+ current
(IK), was reduced by about 60% in
small, medium, and large cells. These data suggest that axotomy-induced
increases in excitability are associated with decreases in
IK and/or decreases in
gK,Ca that are secondary to decreased
Ca2+-influx. Because
IH was reduced by axotomy, changes in
this current do not contribute to increased excitability. The amplitude
and inactivation of IBa in all cell
types was changed more profoundly in animals that exhibited
self-mutilatory behavior (autotomy). The onset of this behavior
corresponded with significant reduction in
IBa of large neurons. This finding
supports the hypothesis that autotomy, that may be related to human
neuropathic pain, is associated with changes in the properties of large
myelinated sensory neurons.
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