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Fig. 5. Presynaptic overexpression of either wild-type or mutant helSyn does not affect facilitation or augmentation at C1-B2 synapses. (A) Sample electrophysiological recording of frequency facilitation at C1-B2 synapses during a train of five action potentials induced at 2 Hz in the presynaptic C1 neuron (lower trace). Note the progressive increase in the amplitude of the summating EPSPs recorded in the B2 neuron (upper trace). Bars: horizontal, 1.5 seconds; vertical, 5 mV upper trace, 20 mV lower trace. (B) The graph shows the mean facilitation index (expressed as the percent ratio between the fifth and the first EPSP during 2 Hz trains) measured in the different experimental groups. No significant change with respect to control conditions is observed after either helSyn-GFP or helSynALA9-GFP overexpression. (C) Sample electrophysiological recording of augmentation induction and decay at C1-B2 synapses. Single action potentials in the C1 neuron are elicited by intracellular depolarizing stimuli delivered at a basal frequency of 0.2 Hz (lower trace) and the corresponding EPSPs evoked in the postsynaptic B2 neuron are simultaneously recorded (upper trace). After some basal stimuli, a train of five action potentials at 10 Hz is induced in the C1 neuron (arrowhead). Two seconds after the train, the basal 0.2 Hz stimulation is resumed. The amplitude of the EPSPs after the train is increased for about 10 seconds. Bars: horizontal, 5 seconds; vertical, 5 mV upper trace, 20 mV lower trace. (D) Time-course of EPSP amplitude changes in augmentation episodes induced in synapses overexpressing either wild-type or mutant helSyn and in control synapses. No significant change in augmentation is observed after either helSyn-GFP or helSynALA9-GFP overexpression with respect to control conditions.
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