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Volume 17, Number 5,
Issue of March 1, 1997
pp. 1633-1641
Copyright ©1997 Society for Neuroscience
Ectopic 2-Adrenoceptors Couple to N-Type
Ca2+ Channels in Axotomized Rat Sensory Neurons
Received Sept. 12, 1996; revised Dec. 16, 1996; accepted Dec. 23, 1996.
Fuad A. Abdulla and
Peter A. Smith
Department of Pharmacology, University of Alberta, Edmonton,
Alberta, Canada T6G 2H7
Dorsal root ganglion (DRG) neurons from control rats or from rats
in which the sciatic nerve had been sectioned were studied by
whole-cell recording techniques. Noradrenaline (10-100
µM) activated -adrenoceptors and increased L-type
Ca2+ channel current in control DRG cells, but this had
little effect on excitability (the number of action potentials
generated by a pulse of current at rheobasic strength). By contrast, in
cells from nerve-damaged animals, noradrenaline activated
2-adrenoceptors, suppressed N-type Ca2+
channel current, and increased excitability. In axotomized cells, it
also reduced total outward current recorded at +70 mV. Because noradrenaline did not affect total outward current recorded in the
presence of the Ca2+ channel blocker Cd2+
(0.5-1 mM), its effects on excitability may result from
reduction of Ca2+-sensitive K+-conductance(s)
following suppression of N-type Ca2+ channel current. The
strongest effects of noradrenaline were seen in small cells and in
cells from animals that exhibited autotomy, a self-mutilatory behavior
that can accompany peripheral nerve damage. Because many of these small
DRG cells may be involved in the transmission of nociceptive
information, changes in coupling between Ca2+ channels and
adrenoceptors may contribute to the generation of the ectopic sensory
nerve activity that has been implicated in the etiology of neuropathic
pain.
Key words:
pain;
nerve injury;
spinal ganglion;
sodium channel;
norepinephrine;
acutely dissociated neurons
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