Journal
BRITISH JOURNAL OF PHARMACOLOGY
Volume 160, Issue 7, Pages 1754-1764Publisher
WILEY
DOI: 10.1111/j.1476-5381.2010.00811.x
Keywords
spinal cord; intrathecal; astrocytes; microglia; tumour necrosis factor; prostaglandin; lipopolysacaride; Toll-like receptor 4; pain
Categories
Funding
- Arthritis Foundation
- NIH [DA21654]
- Swedish Research Council [NS16541, GM64611, U54 GM069338]
- Wenner-Gren Foundations
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Background and purpose: 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. Experimental approach: Toll-like receptor 4 was activated by intrathecal (i.t.) injection of lipopolysaccharide (LPS) and KDO2-Lipid A (KDO2) 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. Key results: Spinal administration of LPS and KDO2 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 KDO2 was attenuated by i.t. administration of ketorolac. Conclusions and implications: Activation of TLR4 induces tactile allodynia, which is probably mediated by TNF released by activated spinal glia.
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