Figure 4.

Presynaptic Ca²⁺ influx is not changed in VGLUT1 KO versus WT autapses. A, Left, Example image of SynGCaMP2 fluorescence in a VGLUT1 KO autapse at baseline (left) and after stimulation with 5 APs at 20 Hz (right). Images are set to the same intensity scale. Scale bars, 10 μm. B, Average SynGCaMP2 ΔF/F₀ responses to a 5 AP train at 20 Hz in a single WT (black) or VGLUT1 KO (red) autapse. n value indicates number of ROIs selected per cell. Inset, Accompanying EPSC responses recorded in each neuron. Depolarization artifacts have been blanked for illustrative purposes. C, Average ΔF/F₀ response to 2, 3, or 5 APs at 20 Hz compared over several VGLUT1 KO (red) or WT (black) autapses, or WT autapses in reduced [Ca²⁺]_e (1.4 mm; blue). n values indicated in graph equal the number of cells. Solid lines indicate linear fits of data. Significance was tested by two-way ANOVA with Bonferroni post hoc test. For all graphs, error bars represent the SEM.