Fig. 2.

Characterization of the synapses involved in postburst facilitation. Postburst enhancement of monosynaptic responses occurs at mossy-fiber synapses onto CA3 pyramidal cells (PC) (A) and interneurons (INs) (B). Single APs induced at 0.1 Hz in a granule cell (GC) (Bottom traces) fail to evoke responses in the synaptically coupled PC or IN (Top trace), but after GC bursting (3 × 40 Hz) single GC APs at 0.1 Hz evoke monosynaptic excitatory currents in target cells (Middle traces; superimposed traces during first 3 min after bursting). (A) IPSCs in PCs were suppressed. (Lower) Plots of the changes over time in synaptic charge transfer, and synaptic failure rate (n = 6 for PCs, n = 10 for INs), with arrows indicating time of GC bursting. (C) In contrast, the IN to CA3 PC synapse is not sensitive to IN bursting. Single APs even at 0.1 Hz in an IN reliably evoke GABAergic unitary responses in a PC (Top trace). IN bursting at 40 Hz does not change transmission (Middle trace). (Lower) Plots of charge transfer and failure rate over time (n = 6). [Scale bars: vertical, 100 pA (PC and IN), 100 mV (GC); horizontal, 20 ms.]