Spinal glial TLR4-mediated nociception and production of prostaglandin E(2) and TNF.
OBJECTIVE
Toll-like receptor 4 (TLR4) expressed on spinal microglia and astrocytes has been suggested to play an important role in the regulation of pain signalling. The purpose of the present work was to examine the links between TLR4, glial activation and spinal release of prostaglandin E(2) (PGE(2)) and tumour necrosis factor (TNF), and the role these factors play in TLR4-induced tactile allodynia.


METHODS
Toll-like receptor 4 was activated by intrathecal (i.t.) injection of lipopolysaccharide (LPS) and KDO(2)-Lipid A (KDO(2)) to rats. Tactile allodynia was assessed using von Frey filaments and cerebrospinal fluid collected through spinal dialysis and lumbar puncture. PGE(2) and TNF levels were measured by mass spectometry and elisa. Minocycline and pentoxifylline (glia inhibitors), etanercept (TNF-blocker) and ketorolac (COX-inhibitor) were given i.t. prior to injection of the TLR4-agonists, in order to determine if these agents alter TLR4-mediated nociception and the spinal release of PGE(2) and TNF.


RESULTS
Spinal administration of LPS and KDO(2) produced a dose-dependent tactile allodynia, which was attenuated by pentoxifylline, minocycline and etanercept but not ketorolac. Both TLR4 agonists induced the spinal release of PGE(2) and TNF. Intrathecal pentoxifylline blunted PGE(2) and TNF release, while i.t. minocycline only prevented the spinal release of TNF. The release of PGE(2) induced by LPS and KDO(2) was attenuated by i.t. administration of ketorolac.


CONCLUSIONS
Activation of TLR4 induces tactile allodynia, which is probably mediated by TNF released by activated spinal glia.
Saito
O
O
Department of Anesthesiology, University of California San Diego, La Jolla, USA.
Svensson
C I
CI
Buczynski
M W
MW
Wegner
K
K
Hua
X-Y
XY
Codeluppi
S
S
Schaloske
R H
RH
Deems
R A
RA
Dennis
E A
EA
Yaksh
T L
TL
D000818:Animals; D001253:Astrocytes / Q000276:immunology / Q000378:metabolism; D001522:Behavior, Animal / Q000187:drug effects; D002853:Chromatography, Liquid; D015232:Dinoprostone / Q000096:biosynthesis* / Q000134:cerebrospinal fluid; D004797:Enzyme-Linked Immunosorbent Assay; D007278:Injections, Spinal; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D017628:Microglia / Q000276:immunology / Q000378:metabolism; D010146:Pain / Q000134:cerebrospinal fluid / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013116:Spinal Cord / Q000276:immunology / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000134:cerebrospinal fluid
C506188:Kdo2-lipid A; D008070:Lipopolysaccharides; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C440499:lipopolysaccharide, Escherichia coli O111 B4; D015232:Dinoprostone