Endogenous PGE₂ regulates membrane excitability and synaptic transmission in hippocampal CA1 pyramidal neurons

The significance of cyclooxygenases (COXs), the rate-limiting enzymes that convert arachidonic acid (AA) to prostaglandins (PGs) in the brain, is unclear, although they have been implicated in inflammatory responses and in some neurological disorders such as epilepsy and Alzheimer's disease. Recent evidence that COX-2, which is expressed in postsynaptic dendritic spines, regulates PGE₂ signaling in activity-dependent long-term synaptic plasticity at hippocampal perforant path-dentate granule cell synapses, suggests an important role of the COX-2-generated PGE₂ in synaptic signaling. However, little is known of how endogenous PGE₂ regulates neuronal signaling. Here we showed that endogenous PGE₂ selectively regulates fundamental membrane and synaptic properties in the hippocampus. Somatic and dendritic membrane excitability was significantly reduced when endogenous PGE₂ was eliminated with a selective COX-2 inhibitor in hippocampal CA1 pyramidal neurons in slices. Exogenous application of PGE₂ produced significant increases in frequency of firing, excitatory postsynaptic potentials (EPSP) amplitude, and temporal summation in slices treated with the COX-2 inhibitor. The PGE₂-induced increase in membrane excitability seemed to result from its inhibition of the potassium currents, which in turn, boosted dendritic Ca²⁺ influx during dendritic-depolarizing current injections. In addition, the PGE₂-induced enhancement of EPSPs was blocked by eliminating both PKA and PKC activities. These findings indicate that endogenous PGE₂ dynamically regulates membrane excitability, synaptic transmission, and plasticity and that the PGE₂-induced synaptic modulation is mediated via cAMP-PKA and PKC pathways in rat hippocampal CA1 pyramidal neurons.