NMDA RECEPTORS AT EXCITATORY SYNAPSES IN THE HIPPOCAMPUS - TEST OF A THEORY OF MAGNESIUM BLOCK

Excitatory postsynaptic currents (EPSCs) were studied using the whole- cell patch-clamp technique to record from rat hippocampal pyramidal ne urons in both slices and dissociated cultures. The voltage- and magnes ium-dependence of the N-methyl-D-aspartate (NMDA) component of the EPS Cs was quantified by measuring the amplitude of this component at a ra nge of holding potentials (-80 mV to 60 or 80 mV) in several bath magn esium concentrations (0.2muM, 0.1, 1 and 10 mM). All of our results we re well-fitted by a theory of magnesium block developed from single-ch annel studies of extrajunctional NMDA channels in culture. It is concl uded that extrasynaptic and subsynaptic NMDA channels both in culture and in situ have identical properties of magnesium block.