Figure 6 HFS in SR allows CA3 inputs to evoke action potential firing in CA2 PNs. A, Traces of extracellular recordings in the CA2 pyramidal layer in response to a 20 V stimulation of SC inputs, before (gray traces) and after an HFS (black traces), illustrating how HFS induces an increase in the PS amplitude (negative peak). B, Average PS amplitude as a function of stimulation intensity before (open circle) and after (filled circle) HFS (with 20 V stimulation: p = 0.01, n = 5; with 30 V stimulation: p = 0.006, n = 5). C, Time course of average normalized PS amplitude recorded in CA2 pyramidal layer in response to a 20 V stimulation of SC inputs, showing a long-lasting increase in PS amplitude after HFS (p = 0.01, n = 5). D, Traces of whole-cell current-clamp recordings in a CA2 pyramidal cell in response to a train of stimulations (five pulses at 100 Hz) of SC inputs, illustrating how APs can be evoked in CA2 neurons after HFS (black traces) but not before HFS (gray traces). E, Average number of APs per train at different stimulation intensities, showing how a five-pulse train at 100 Hz of the SC inputs does not trigger APs in CA2 PNs before HFS (open circles) but induces APs after HFS (filled circles, with 30 V stimulation: from 0 to 1.15 ± 0.3 APs per train after HFS, p = 0.012, n = 6). F, An HFS increases the percentage of CA2 PNs firing at least one AP during the train (with 30 V stimulation: from 0% to 80% of cells firing APs). G, Traces of whole-cell current-clamp recordings in a CA2 PN in response to a stimulation train (five pulses at 100 Hz) of SC inputs in the presence of the DOR antagonist ICI 174864 (2 μm), illustrating how the application of ICI 174864 prevents the induction of APs in CA2 PNs after HFS (black traces). H, Average number of APs per train at different stimulation intensities in the presence of the DOR antagonist before HFS (open circles; with 0–30 V stimulations: 0 APs per train) and after HFS (filled circles; with 30 V stimulation: 0.15 ± 0.15 AP per train after HFS, p = 0.37, n = 5). I, In the presence of ICI 174864, HFS does not induce a large increase in the percentage of CA2 PNs firing at least one AP during the train (with 10 V stimulation: 0% of cells firing APs before and after HFS; with 20 and 30 V stimulation: from 0% to 20% of cells firing APs). Error bars indicate the SEM in all panels.