Figure 2. Presynaptic facilitation contributes to 'conditional detonation' at the hippocampal mossy fiber–CA3 pyramidal neuron synapse.
(A) Pyramidal neuron EPSPs and action potentials evoked by a short train of stimuli delivered to the presynaptic bouton (top, three stimuli delivered at 50 Hz). Ten consecutive postsynaptic responses are shown superimposed (40 s repetition interval). Note that the first presynaptic stimulus was unable to discharge the postsynaptic neuron, whereas the third stimulus reliably initiated firing. (B) Probability of postsynaptic action potential initiation as a function of presynaptic stimulus number (50-Hz stimulation of bouton) for experiments like that shown in A (points connected by lines for clarity, eight pairs). (C) EPSCs recorded in the pyramidal neuron in response to 50-Hz stimulation of the presynaptic bouton, showing marked facilitation of transmitter release (five consecutive EPSCs shown superimposed, 20 s repetition interval, same recording as in A). (D, E) Summary graphs for absolute (D) and normalized EPSC peak amplitude (E) from experiments like that shown in C (13 pairs). Error bars indicate SEM.