Figure 7.

GABA increases release probability at parallel fiber stellate cell synapses. A, Top, Image of a stellate cell filled with Alexa-594 and Fluo-5F. The stimulating pipette and iontophoretic pipette are also visible (digitally enhanced for clarity). B, Magnified image of a single dendrite (top) and line scan across the long axis of the dendrite at 500 Hz showing red and green (calcium dependent) fluorescence (bottom). Arrow indicates the time of parallel fiber stimulation. Calibration: 50 ms. C, Average spatial distribution of the peak green fluorescence in the synapse shown in B from the first 10 ms following stimulation. The fluorescence profile is fit with a Gaussian curve (red). D, Top, Average postsynaptic calcium responses of all trials in control conditions (black) and following GABA iontophoresis (red). Bottom, Average of success trials only (upper traces) or failure trials only (lower trace). E, Average peak calcium responses across all cells when all trials, successes only, or failures only are average. F, Top, The average postsynaptic calcium response following paired-pulse parallel fiber stimulation when there is a success on the first stimulus (black) or a success on the second stimulus following a failure on the first (red). Bottom, Average of all EPSCs from the same cell. G, Average (bars) and individual cell (circles) changes in response probability due to GABA iontophoresis in control conditions or EGTA. Data taken from the same cells are connected by lines.