AbstractBackground and purpose:
Receptor subtypes involved in PGE2-induced nociception are still controversial. The present study investigated the prostanoid E receptor (EP) subtypes and the protein kinase (PK) pathways involved in the nociception induced by PGE2 injection in the mouse paw.Experimental approach:
Paw-licking and mechanical allodynia were measured in vivo and protein kinase activation ex vivo by Western blots of extracts of paw skin.Key results:
Intraplantar (i.pl.) injection of PGE2 into the mouse paw caused nociceptive behaviour of short duration with mean ED50 of 1.43 nmol. PGE2 produced a longer-lasting mechanical allodynia, with an ED50 of 0.05 nmol. Intraplantar injection of antagonists at EP3 or EP4, but not at EP1 or EP2 receptors inhibited PGE2-induced paw-licking. Paw-licking caused by PGE2 was blocked by an inhibitor of PKA but only partially decreased by inhibition of the extracellular-regulated kinase (ERK). Selective inhibitors of PKC, c-Jun N-terminal kinase (JNK) or p38, all failed to affect PGE2-induced paw-licking. An EP3 antagonist inhibited PGE2-induced mechanical allodynia. However, inhibitors of PKA, PKC or ERK, but not p38 or JNK, also partially inhibited PGE2-induced mechanical allodynia. Western blot analyses confirmed that i.pl. injection of PGE2 activated PKA, PKCα, and mitogen activated kinases (MAPKs) in the paw. Co-treatment with EP3 or EP4 receptor antagonists reduced PGE2-induced PKA and ERK, but not PKCα activation.Conclusions and Implications:
The present results indicate that the nociceptive behaviour and mechanical allodynia caused by i.pl. PGE2 are mediated through activation of distinct EP receptors and PK-dependent mechanisms.