MODULATION OF THE INVITRO ELECTROPHYSIOLOGICAL EFFECT OF CORTICOSTERONE BY EXTRACELLULAR CALCIUM IN THE HIPPOCAMPUS

The electrophysiological effects of various concentrations of corticosterone (CORT) on the hippocampus were investigated using extracellular recordings from CA1 hippocampal slice preparations subjected to four different extracellular concentrations of calcium. In all cases, the CORT effect was manifested by a PS amplitude decrease without affecting the slope of either the input volley or the EPSP. Our results showed that, for the lowest extracellular calcium concentrations (1.3 and 2.5 mM), the inhibitory effect of CORT on the PS amplitude appeared only with the supra-physiological 10,000 nM CORT concentration, whereas for the highest ones (3.13 and 5.32 mM) this effect was observed, respectively, with 5 and 0.05 nM CORT concentrations. The antiglucocorticoid RU 486, used in combined application with CORT, blocked the electrophysiological effect of CORT. The possible involvement of calcium-dependent mechanisms at the CORT receptor level or in the final cellular response are discussed.