Figure 2.

Homeostatic changes in presynaptic calcium influx detected with SyGCaMP2. A, Fluorescence image of cultured hippocampal neurons expressing SyGCaMP2 (left) and pseudocolored images showing the relative change in fluorescence 0.3 s from the beginning of a train of 3 APs delivered at 20 Hz. B, The response to 3 APs was larger in a culture treated with TTX for 2 d. Note the variability in the amplitude of the presynaptic calcium signal between different boutons. Scale bar, 10 μm. C, Averaged SyGCaMP2 response to 1 AP (left) and 3 APs (right). Control cultures are black (n = 805 synapses), TTX-treated cultures are red (n = 1200), and gabazine-treated cultures are green (n = 386). Error bars are SEM. D, Peak amplitude of the SyGCaMP2 signal plotted as a function of the number of APs delivered at 20 Hz. Line fits have the following slopes: control (black), 0.078 ± 0.003; TTX (red), 0.104 ± 0.003; gabazine (green), 0.063 ± 0.004. Error bars are SEM.