Hippocampal synaptic plasticity was modulated by exposure to isoflurane (i.e., long-term potentiation impairment and long-term depression improvement). (A) Experimental design. Slopes of field excitatory postsynaptic potentials (fEPSPs) were electrophysiologically measured 7 days after a 2-h exposure to 1.8% isoflurane (Iso), using the MED64 system. (B) The fEPSPs slopes observed after the application of a high-frequency stimulus (100 Hz, 2 trains of stimulation for 1 s, 25 s apart) are shown. (C) The fEPSPs slopes observed after the application of an intermediate-frequency stimulus (10 Hz, 900 pulses) are shown. (D) The fEPSPs slope observed after the application of a low-frequency stimulus (1 Hz, 900 pulses) are shown. (E) Summarized graph of the synaptic plasticity in hippocampal fEPSPs. Percentage changes of normalized fEPSPs slopes between 36 and 40 min after the stimulus are shown against stimulus frequency (isoflurane, F[1, 30] = 48.464, P < 0.001; stimuli, F[2, 30] = 50.975, P < 0.001; isoflurane × frequency, F[2, 30] = 4.270, P = 0.023). High-frequency stimulus–induced long-term potentiation was impaired significantly (n = 6 per group; *P < 0.001). Intermediate-frequency stimulus induced no significant changes (n = 6 per group; P = 0.86). Low-frequency stimulus–induced long-term depression was enhanced significantly (n = 6 per group; #P = 0.003). All statistical analyses were performed using two-way factorial ANOVA (isoflurane × frequency, significance level was set at P < 0.05) followed by Student t tests (significance level was set at 0.05/3 = 0.0167 with Bonferroni correction). Data are shown as mean ± SEM.