Activation of the spinal
phospholipase A(2) (PLA(2)) -
cyclooxygenase (COX) -
prostaglandin signaling pathway is widely implicated in nociceptive processing. Although the role of spinal COX
isoforms in
pain signal transmission has been extensively characterized, our knowledge of PLA(2)
enzymes in this cascade is limited. Among all PLA(2) groups, cytosolic
calcium-dependent PLA(2) group IVA (cPLA(2)IVA) appears to be the predominant PLA(2)
enzyme in the spinal cord. In the present study we sought to (i) characterize anatomical and cellular distribution and localization of cPLA(2)IVA in dorsal horn of rat spinal cord, (ii) verify efficacy and selectivity of intrathecal (IT) delivery of an
antisense oligonucleotide (AS) targeting rat cPLA(2)IVA
mRNA on spinal expression of this
enzyme, and (iii) examine the effect of down-regulation of spinal cPLA(2)IVA on peripheral tissue injury-induced
pain behavior. Here we demonstrate that cPLA(2)IVA is constitutively expressed in rat spinal cord, predominantly in dorsal horn neurons and oligodendrocytes but not in astrocytes or microglia.
Intrathecal injection of AS significantly down-regulated both
protein and gene expression of cPLA(2)IVA in rat spinal cord, while control missense
oligonucleotide (MS) had no effect. Immunocytochemistry confirmed that the reduction occurred in neurons and oligodendrocytes. cPLA(2)IVA AS did not alter expression of several other PLA(2)
isoforms, such as secretory PLA(2) (groups IIA and V) and
calcium-independent PLA(2) (group VI), indicating that the AS was specific for cPLA(2)IVA. This selective knockdown of spinal cPLA(2)IVA did not change acute nociception (i.e. paw withdrawal thresholds to acute thermal stimuli and intradermal
formalin-induced first phase flinching), however, it significantly attenuated
formalin-induced
hyperalgesia (i.e. second phase flinching behavior), which reflects spinal sensitization. Thus the present findings suggest that cPLA(2)IVA may specifically participate in spinal nociceptive processing.