PAIRING OF PRESYNAPTIC AND POSTSYNAPTIC ACTIVITIES IN HIPPOCAMPAL CA1 NEURONS INDUCES LONG-TERM MODIFICATIONS OF NMDA RECEPTOR-MEDIATED SYNAPTIC POTENTIAL

An in vitro slice preparation of rat hippocampus was used to study the long-term modifications of pharmacologically isolated N-methyl-D-aspartate (NMDA) receptor-mediated excitatory postsynaptic potential (EPSP(NMDA)). Intracellular recordings were made from CA1 pyramidal cells in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 muM) and picrotoxin (50 muM) which block non-NMDA and GABA(A) receptors, respectively. Pairing of low-frequency EPSP(NMDA) with postsynaptic depolarization induced a long-term depression (LTD) of EPSP(NMDA). The maximal reduction of EPSP(NMDA) amplitude amounted to 81.3% of the control 1 min after the pairing. When low-frequency synaptic stimulation was paired with strong postsynaptic depolarization, a long-term potentiation (LTP) of EPSP(NMDA) could be induced. These results suggest that the induction of long-term modifications of EPSP(NMDA) has at least a postsynaptic component.