Prostaglandin E2 receptor EP4 contributes to inflammatory pain hypersensitivity

Prostaglandin E-2 (PGE(2)) is both an inflammatory mediator released at the site of tissue inflammation and a neuromodulator that alters neuronal excitability and synaptic processing. The effects of PGE(2) are mediated by four G-protein-coupled EP receptors (EP1-EP4). Here we show that the EP4 receptor subtype is expressed by a subset of primary sensory dorsal root ganglion (DRG) neurons, and that its levels, but not that of the other EP1-3 subtypes, increase in the DRG after complete Freund' adjuvant-induced peripheral inflammation. Administration of both an EP4 antagonist [AH23848, (4Z)-7-[(rel-1S,2S,5R)-5-((1,1 '-biphenyl-4-yl)methoxy)-2-(4-morpholinyl)-3oxocyclopentyl]-4-heptenoic acid] and EP4 knockdown with intrathecally delivered short hairpin RNA attenuates inflammation-induced thermal and mechanical behavioral hypersensitivity, without changing basal pain sensitivity. AH23848 also reduces the PGE(2)-mediated sensitization of capsaicin-evoked currents in DRG neurons in vitro. These data suggest that EP4 is a potential target for the pharmacological treatment of inflammatory pain.