Journal of Neurophysiology, Vol 66, Issue 2 363-368, Copyright © 1991 by APS
Different mechanical transduction mechanisms for the immediate and delayed responses of rat C-fiber nociceptors
D. M. White and J. D. Levine
Department of Medicine, University of California, San Francisco 94143.
1. In this electrophysiological study, action potentials from single
C-fibers were recorded in fine filaments teased from the rat saphenous
nerve. We evaluated the effect of pharmacological agents on the responses
of C-fiber mechanoheat nociceptors (C-MH; n = 53) after sustained
suprathreshold and subthreshold stimuli. 2. Sustained suprathreshold
mechanical stimuli elicit an immediate burst of activity that quickly
adapts to a low-level firing that is maintained during the stimulus.
Sustained subthreshold stimuli activate C-MHs after a delay and elicit a
constant, low-level firing. 3. Gentamicin, a known suppressor of
mechanosensory cell activity, blocked the initial rapid burst response to
suprathreshold stimuli (n = 11) but had no effect on the adaptive low-level
firing. The latency of the delayed activation of C-MHs induced by sustained
subthreshold stimuli was not affected by gentamicin. 4. Sphingosine, a
protein kinase inhibitor, increased the latency of the delayed activation
of C-MHs (n = 7) to sustained subthreshold stimuli; phorbol 12-myristate
13-acetate (TPA), a protein kinase C activator, decreased the latency of
the delayed activation of C-MHs (n = 9); and 4 alpha-phorbol, an inactive
isomer of TPA, had no effect on the latency of the delayed activation (n =
7). Sphingosine, TPA, and 4 alpha-phorbol had no affect on the initial
burst response induced by suprathreshold stimuli. 5. K+ channel blockers,
4-aminopyridine (n = 9) and noxiustoxin (n = 5), decreased the latency of
the delayed activation of C-MHs to sustained subthreshold stimuli but had
no effect on the initial burst response of C-MHs to suprathreshold
stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
