Current work has shown the importance of spinal
cyclooxygenase (COX) products in facilitatory processes leading to tissue injury induced
hyperalgesia. This cascade must originate with free
arachidonic acid (AA) released by the activity of spinal
phospholipase A2s (PLA2). In the present work, we studied the role of PLA2s in spinal sensitization. We first demonstrate the presence of constitutive
mRNA in the spinal cord for PLA2 Groups IB, IIA, IIC, IVA, V and VI by reverse transcription-polymerase chain reaction (RT-PCR) and sequencing. Using quantitative-PCR, we found that Group IVA cPLA2 and Group VI iPLA2 are the predominant PLA2 messages in the spinal cord. Western blotting and activity assays specific for Group IVA cPLA2 and Group VI iPLA2 verified the presence of these
enzymes. PLA2 activity in spinal cord homogenates was suppressed by
methyl arachidonyl fluorophosphonate (MAFP) and arachidonyl trifluoromethylketone (
AACOCF3), mixed inhibitors of Group IVA cPLA2 and Group VI iPLA2 as well as by
bromoenol lactone (BEL), a Group VI iPLA2 inhibitor. The spinal expression of PLA2
mRNA or
protein was not altered in the face of peripheral
inflammation. Secondly, we showed that intrathecal (i.t.) administration of MAFP and
AACOCF3, but not BEL, dose-dependently prevented
thermal hyperalgesia induced by intraplantar
carrageenan as well as
formalin-induced flinching. Finally, i.t. injection of
AACOCF3, at antihyperalgesic doses, decreased the release of
prostaglandin E2 (
PGE2) into spinal
dialysate evoked by i.t.
NMDA, while i.t. injection of BEL had no effect. Taken together, this work points to a role for constitutive Group IVA cPLA2 in spinal nociceptive processing.