The predominant phospholipase activity present in rat hippocampus is a calcium-independent phospholipase A2 (302.9 +/- 19.8 pmol/mg.min for calcium-independent phospholipase A2 activity vs. 14.6 +/- 1.0 pmol/mg.min for calcium-dependent phospholipase A2 activity). This calcium-independent phospholipase A2 is exquisitely sensitive to inhibition by the mechanism-based inhibitor, (E)-6-(bromomethylene)-tetrahydro-3-(1-naphthalenyl)-2H-pyran -2-one (BEL). Moreover, treatment of hippocampal slices with BEL prior to tetanic stimulation prevents the induction of LTP (40.8 +/- 5.6% increase in excitatory post-synaptic potential (EPSP) slope for control slices (n = 6) vs. 5.8 +/- 8.5% increase in EPSP slope for BEL-treated slices (n = 8)). Importantly, LTP can be induced following mechanism-based inhibition of phospholipase A2 by providing the end product of the phospholipase A2 reaction, arachidonic acid, during the application of tetanic stimulation. Furthermore, the induction of LTP after treatment with BEL is dependent on the stereoelectronic configuration of the fatty acid provided since eicosa-5,8,11-trienoic acid, but not eicosa-8,11,14-trienoic acid, rescues LTP after BEL treatment (37.6 +/- 16.1% increase in EPSP slope for eicosa-5,8,11-trienoic acid vs. -3.7 +/- 5.2% increase in EPSP slope for eicosa-8,11,14-trienoic acid). Collectively, these results provide the first demonstration of the essential role of calcium-independent phospholipase A2 in synaptic plasticity.