Figure 1. A fraction of the evoked postsynaptic current recorded in hippocampal CA1 pyramidal neurons is resistant to glutamate and GABA receptor antagonists.

A, graph showing the changes in size of the compound postsynaptic current (cPSC) recorded before and after bath application of NBQX (5 μM), R-CPP (10 μM) and bicuculline (10 μM) in an organotypic culture. The traces on the right are representative evoked response recorded before (a) and after (b) drug application. As shown, a small current measuring 2.9 ± 0.4 % of the initial cPSC could still be evoked following drug application (n = 10; the 10 cells tested exhibited the residual current). This residual current was obtained in 39 out of 41 cells in organotypic slice cultures and in 9 out of 16 cells in acutely prepared slices (mean size: 1.4 ± 0.4 %). B, application of additional antagonists of excitatory and inhibitory transmission did not affect the residual current. The graph shows the results of 3 experiments made on organotypic cultures in which CNQX (20 μM), D-AP5 (100 μM) and picrotoxin (100 μM) were added to previous concentrations of NBQX (5 μM), R-CPP (20 μM) and bicuculline (20 μM). Data are means ±s.e.m. of the amplitude of the evoked current. The trace on the right is a representative response recorded in the presence of these antagonists.