Figure 1. Single, brief MF bursts potentiate monosynaptic MF-EPSCs in CA3 FF-INs for several seconds. A, Schematic representation of the recording configuration for unitary MF responses in CA3 neurons. Presynaptic patch-clamp recording was obtained from a single giant MF terminal (most of these originate from DG GCs; Fig. 1-1) or a single CA3 GC (somatic recording; these cells are rarer but easier to record than the MF terminals); the postsynaptic cell was an FF-IN. MF output was first measured with a control stimulus, followed by a single 2–20 AP burst (150 Hz); after various time delays (0.1–13.5 s), which approximated the typical physiological inactivity periods in GCs in vivo, a test response was evoked. Right, Example traces of single-AP-evoked control and test EPSCs in an identified FF-IN (the illustrated recordings were from an IvyC; for the anatomy of the presynaptic and postsynaptic cells, see Fig. 1-1). In most cases, control and test pulses contained 3 APs at 20 Hz to gain insight into possible changes in short-term plasticity after the bursts; plots in this and subsequent figures show responses to the first APs in the triplet, except in Figure 4C, D. B, Time course of the relative amplification of monosynaptic MF-EPSCs after single 15 AP presynaptic bursts in the same individual MF. Relative postburst EPSC amplitudes are shown (i.e., control relative amplitudes are 1, dashed line). The x axis indicates the time of the test pulse after the burst. The graph includes all data points (n = 280, first APs) from identified FF-IN pairs (n = 78 pairs; including IvyCs: n = 55 pairs; AACs: n = 10; PV+BC: n = 5; CCK+IN, n = 8; for separate analysis of the burst-induced amplification in different postsynaptic cell types, see Figs. 1-1, 1-2, 1-3, and 1-4). Insets, Example test responses in blue at different postburst delays; same postsynaptic IvyC as in A; control traces are black. C, Dependence of the postburst potentiation on AP numbers within the burst (from n = 99 data points from n = 28 pairs). Brown curve indicates the exponential fit of the data (R2 = 0.966). Gray area represents the typical range of GC bursts in vivo. Insets, Example test and control traces and the time course of the changes of the responses after 3, 5, 9, and 15 AP bursts. D, Effects of single presynaptic bursts consisting of 8 APs at 20, 40, 80, and 150 Hz, on the same MF-FF-IN pairs (n = 7). E, Effects of single bursts, whose patterns were obtained from in vivo recorded identified GCs: #1, 6 APs with 3.7, 7.5, 4.54, 6.98, and 5.88 ms interspike intervals (Henze et al., 2002); #2, 4 APs with 4, 6, and 9 ms interspike intervals (Pernía-Andrade and Jonas, 2014); #3, 5 APs with 6, 8, 11, and 15 ms interspike intervals (Diamantaki et al., 2016); for comparison, the effect of a 6 AP 150 Hz burst is also shown. The effects were measured with each realistic burst protocol in the same pairs (n = 8 pairs, 3.6 s after burst).