Does the antihyperalgesic disruptor of endothelial cells, octoxynol-9, alter nociceptor function?
The vasoactive mediator, endothelin-1, elicits a novel form of hyperalgesia, stimulation-dependent hyperalgesia. Acting on its cognate receptor on the vascular endothelial cell, endothelin-1 produces a state in which mechanical stimulation now elicits release of pronociceptive mediators from endothelium that, in turn, acts at receptors on sensory neurons. The only evidence that octoxynol-9, a surface-active agent that attenuates both endothelial cell function and stimulus-dependent hyperalgesia, does not affect nociceptors is indirect (i.e., octoxynol-9 treatment did not affect behavioral nociceptive threshold or hyperalgesia induced by agents that act directly on nociceptors). To help address the question of whether the attenuation of stimulation-dependent hyperalgesia by octoxynol-9 treatment is due to alteration of nociceptor function, we used in vivo single-fiber electrophysiological recordings. Consistent with our previous behavioral observations, we observed no significant effect of octoxynol-9 on mechanical threshold in nociceptors, their response to sustained suprathreshold mechanical stimulation, conduction velocity, and change in mechanical threshold in response to the direct-acting hyperalgesic agent, PGE2. Although octoxynol-9 did not produce a biologically meaningful change in parameters of nociceptor function, we cannot exclude the possibility of a type II error. However, our data provide preliminary evidence of no effect of octoxynol-9 on nociceptors and are consistent with the suggestion that the primary action of octoxynol-9 in our studies is due to its action on the endothelium.
Department of Oral and Maxillofacial Surgery, University of California, San Francisco, California; Division of Neuroscience, University of California, San Francisco, California.
Xiaojie
X
Chen
Department of Oral and Maxillofacial Surgery, University of California, San Francisco, California; Division of Neuroscience, University of California, San Francisco, California.
Paul G
PG
Green
Department of Oral and Maxillofacial Surgery, University of California, San Francisco, California; Department of Medicine, University of California, San Francisco, California; and Division of Neuroscience, University of California, San Francisco, California jon.levine@ucsf.edu.
Jon D
JD
Levine
D000200:Action Potentials; D000818:Animals; D042783:Endothelial Cells / Q000187:drug effects; D006930:Hyperalgesia / Q000378:metabolism; D008297:Male; D059225:Nociception; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D017830:Octoxynol / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012684:Sensory Thresholds; D013501:Surface-Active Agents / Q000494:pharmacology*
D013501:Surface-Active Agents; D017830:Octoxynol
electrophysiology; endothelium; skeletal muscle; stimulus-dependent hyperalgesia