Central release of tracer after noxious stimulation of the skin suggests non-synaptic signaling by unmyelinated fibers.
Injury to a peripheral nerve causes central changes of various nature and complexity reflecting activation of multiple signaling mechanisms. In a previous study we reported that nerve lesion triggers central release of a tracer, wheatgerm-agglutinin conjugated to horse-radish peroxidase, by unmyelinated fibers in the spinal cord. The released tracer occupies the space between nerve terminals and dendrites without extending into the synaptic cleft. We interpreted this to suggest release of unidentified endogenous factor(s) at nonsynaptic sites, which may contribute to the signaling of peripheral injury to the central nervous system. For such signaling to occur, a message must first be communicated along the axon. This message may depend on axonal transport and/or altered electrical activity. In pilot experiments we observed that application of tetrodotoxin (to block impulse conduction) to the intact nerve did not result in tracer release. We hypothesized that the message might be the sustained discharge of C fibers that occurs after injury. We show here that selective activation of C fibers (by applying mustard oil to the hindlimb of anesthetized rats) causes central release of tracer previously transported from the sciatic nerve to superficial laminae of the dorsal horn.
Valtschanoff
J G
JG
Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599, USA.
Weinberg
R J
RJ
Rustioni
A
A
D000818:Animals; D008297:Male; D009149:Mustard Plant; D009412:Nerve Fibers / Q000502:physiology*; D010936:Plant Extracts / Q000494:pharmacology; D010938:Plant Oils; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve; D015398:Signal Transduction / Q000502:physiology*; D012867:Skin; D013126:Spinal Nerve Roots; D013779:Tetrodotoxin / Q000633:toxicity
D010936:Plant Extracts; D010938:Plant Oils; D013779:Tetrodotoxin; C027793:mustard oil