LONG-TERM DEPRESSION IN THE HIPPOCAMPAL CA1 REGION IS ASSOCIATED WITH EQUAL CHANGES IN AMPA AND NMDA RECEPTOR-MEDIATED SYNAPTIC POTENTIALS

In the CA1 hippocampal region low-frequency (1 - 2 Hz) afferent activation leads to a long-term depression of excitatory synaptic potentials that is induced by calcium influx through postsynaptic N-methyl-D-aspartate receptor channels. In the present experiments using 2- to 3-week-old rats, long-term depressions of field excitatory postsynaptic potentials mediated by amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and by N-methyl-D-aspartate receptor channels were examined in parallel, using a perfusion solution containing low concentrations of an AMPA receptor antagonist and of magnesium (0.1 mM). These experiments revealed that long-term depression was associated with equal relative changes in the two components of the field potential, compatible with a presynaptic location of the expression mechanism for the long-term depression.