Reciprocal suppression of AMPA and NMDA components of EPSP in the CA1 area of rat hippocampal slices in vitro

The interaction between N-methyl-d-aspartate (NMDA)- and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-dependent components of excitatory potsynaptic potentials (EPSP) was studied in rat hippocampal slices, Responses evoked by stimulation of the collateral commissural fibers were recorded in the radial layer of the CAI area. Contribution of the NMDA component was changed by application of solutions with different concentrations of magnesium. In solutions with low magnesium concentration, when both AMPA and NMDA components contribute significantly to EPSP, suppression of one of the components by application of selective antagonist resulted in increase in the area of another component. Thus, the sum of pharmacologically isolated AMPA and NMDA components was significantly higher than the control EPSP, For example, at 0.1 mM of magnesium in the extracellular solution the sum of the components was 340+/-120% of the control EPSP (p < 0.01, N = 6). The data imply that under the control conditions the EPSP components suppress each other. The mutual suppression of the AMPA and NMDA component of the EPSP can be an important factor which influences the conductivity and plastical properties of central glutamatergic synaptic pathways.