Tumor necrosis factor causes persistent sensitization of joint nociceptors to mechanical stimuli in rats.
OBJECTIVE
During inflammation in the joint, normal joint movements are usually painful. A neuronal mechanism for this form of mechanical hyperalgesia is the persistent sensitization of joint nociceptors to mechanical stimuli. Because tumor necrosis factor (TNF) is a major mediator of joint inflammation, we undertook the present study both to explore the potential of TNF to sensitize joint nociceptors to mechanical stimuli and to address the cellular mechanism involved.


METHODS
In anesthetized rats, action potentials (APs) were recorded from sensory nociceptive Aδ fibers and C fibers supplying the knee joint. We monitored responses to rotation of the knee joint at innocuous and noxious intensities. TNF, etanercept, and a p38 inhibitor were injected into the knee joint, and the cyclooxygenase (COX) inhibitor diclofenac was administered intraperitoneally. APs were also recorded in isolated cultured dorsal root ganglion (DRG) neurons in order to test for changes in neuronal excitability induced by TNF.


RESULTS
A single application of TNF into the normal knee joint caused a significant persistent sensitization of nociceptive sensory fibers to mechanical stimuli applied to the joint. This effect was dose dependent. It was prevented by coadministration of etanercept or by an inhibitor of p38, and it was attenuated by systemic application of a COX inhibitor. Patch clamp recordings from isolated DRG neurons showed a rapid increase in neuronal excitability induced by TNF.


CONCLUSIONS
TNF can induce a long-lasting sensitization of joint nociceptors to mechanical stimuli and thus can induce long-lasting mechanical hyperalgesia in joints. TNF can act directly on neurons, underscoring its role as a sensitizing pain mediator.
Richter
Frank
F
Jena University Hospital, Friedrich Schiller University of Jena, Jena, Germany.
Natura
Gabriel
G
Löser
Stefan
S
Schmidt
Katarina
K
Viisanen
Hanna
H
Schaible
Hans-Georg
HG
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D002478:Cells, Cultured; D004008:Diclofenac / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D000068800:Etanercept; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007074:Immunoglobulin G / Q000494:pharmacology; D007270:Injections, Intra-Articular; D007719:Knee Joint / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D023421:Models, Animal; D009619:Nociceptors / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018124:Receptors, Tumor Necrosis Factor; D013314:Stress, Mechanical; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
D000894:Anti-Inflammatory Agents, Non-Steroidal; D007074:Immunoglobulin G; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D004008:Diclofenac; D048051:p38 Mitogen-Activated Protein Kinases; D000068800:Etanercept