Postsynaptically synthesized prostaglandin E2 (PGE2) modulates hippocampal synaptic transmission via a presynaptic PGE2 EP2 receptor

Increasing evidence suggests that cyclooxygenase-2 (COX-2) is involved in synaptic transmission and plasticity, and prostaglandin E2 (PGE2) is a key molecule in COX-2-meduated synaptic modification. However, the precise mechanisms, in particular, which subtypes of PGE2 receptors (EPs) mediate the PGE2-induced synaptic response, are not clear. Recently, we demonstrated that EPs are expressed heterogeneously in the hippocampus, and EP2/4 are mainly expressed in presynaptic terminals. Here, we report that PGE2 increased synaptic stimulus-evoked amplitudes of EPSPs in hippocampal slices and frequency of miniature EPSCs (mEPSCs) in hippocampal neurons in culture. These actions were mimicked by an EP2 agonist and attenuated by protein kinase A inhibitors. Decrease of EP2 expression through silencing the EP2 gene eliminated PGE2-induced increase of the frequency of mEPSCs. COX-2 and microsomal PGE synthase-1 (mPGES-1) and mPGES-2 are present in postsynaptic dendritic spines, because they are colocalized with PSD-95 (postsynaptic density-95), a postsynaptic marker. In addition, the frequency of mEPSCs was enhanced in neurons pretreated with interleukin-1 beta or lipopolysaccharide, which elevated expression of COX-2 and mPGES-1 and produced PGE2, and this enhancement was inhibited by a COX-2 inhibitor that inhibited production of PGE2. Our results suggest that PGE2 synthesized by postsynaptically localized COX-2 functions as a retrograde messenger in hippocampal synaptic signaling via a presynaptic EP2 receptor.