Fig. 2

Short-term synaptic plasticity (fEPSP) depends on stimulation intensity and highly differs between the DH and the VH. Short-term changes in fEPSP induced by a ten-pulse train delivered at three stimulation intensities (subthreshold, suprathreshold and submaximal synaptic responses indicated by open circles, filled circles and diamonds respectively) applied at stimulation frequencies from 0.1 to 100 Hz are shown for the DH and the VH (upper and lower panel respectively). In all diagrams but the two bottom right graphs, fEPSP changes are plotted as a function of stimulus number. The bottom right diagrams in the two panels show the average value of fEPSP changes produced by the 8th–10th stimuli (steady state response) plotted as a function of stimulation frequency. The intensity of stimulation current significantly affected steady-state changes of fEPSP at 5–100 Hz in DH (one-way ANOVA across stimulation intensity, from a minimum F = 8.76, p < 0.005 at 5 Hz to a maximum F = 69.9, p < 0.001 at 50 and 75 Hz). Similarly, stimulation current intensity significantly affected steady-state changes of fEPSP at 10-100 Hz in VH (one-way ANOVA across stimulation intensity, from a minimum F = 4.1, p < 0.05 at 10 Hz to a maximum F = 22.25 at 20 Hz; p < 0.001). Also, the results of statistical comparison of all responses evoked along the stimulation train by the three different stimulation current intensities are shown by horizontal bars (MANOVA along the entire train of responses and independent t-test of individual responses along the train, p < 0.05). Specifically, bars above and below the data curves show the stimulation epoch in which significantly different responses were observed between subthreshold and suprathreshold stimulation (bars above the curves) and suprathreshold and submaximal stimulation (bars below the curves). Note that steady-states of fEPSP changes (i.e. averages of 8–10th responses) shown in bottom-right graphs in the two panels, greatly differ between DH and VH especially when evoked by subthreshold and suprathreshold stimulation intensities (see also Fig. 3). Data presented in the three stimulation intensities (subthreshold, suprathreshold and submaximal) were obtained from (slices/rats): 10/5, 11/6 and 9/4 in DH and 11/6, 11/6 and 8/5 in VH