Corticosterone (CORT) can alter several electrophysiological properties in the hippocampus. Few studies have reported the effects of CORT on hippocampal long-term potentiation (LTP). In the CA1 region of the hippocampal slice, we studied the relative increase in population spike (PS) amplitude after inducing tetanus (PS-LTP) in control conditions and in the presence of CORT (0.5 nM or 5 microM). Two perifusion mediums were used which differed in calcium concentration (M1:Ca 2.5 mM; M2: Ca 3.1 mM). In the control slices, the PS-LTP amplitude was greater in the M1 medium. With the low CORT concentration (0.5 nM), the PS-LTP amplitude was greater than in control conditions in the M2 medium only. A similar PS-LTP amplitude increase was also observed in the M2 medium after application of 0.5 nM aldosterone (type I receptor analog). With the high CORT concentration (5 microM), PS-LTP amplitude decreased in the two conditions. This effect was reversed by co-application of RU486 (type II receptor antagonist). These results demonstrate that CORT can modulate PS-LTP via its two types of hippocampal CORT receptors, depending on the concentration applied. They also showed that the extracellular calcium concentration may contribute to the functional change induced by CORT.