(A) Sample 3D-SIM images of striatal brain sections of Syt-1 control and Syt-1 cKODA mice stained for the dopamine axon marker TH and the release site marker Bassoon. Volume rendered reconstructions (10 × 10 × 2 µm3, top, all Bassoon is shown), surface rendering of the same volumes (middle, all Bassoon is shown), and zoomed-in volumes (bottom, 5 × 3 × 2 µm3 in front view and rotated by +90° along the x-axis, only including Bassoon clusters with >40% volume overlap with TH) are shown. (B–E) Quantification of the fraction of the image volume covered by TH (B), TH axon length (C), Bassoon cluster densities (D) and Bassoon cluster volumes (E). For the shuffled controls in D and E, each Bassoon object was randomly relocated 1000 times within a volume of 1 × 1 × 1 µm3, and the actual Bassoon densities and volumes were compared to the average of the shuffled controls. Syt-1 control: n = 43 images/5 slices/3 mice, Syt-1 cKODA n = 41/5/3. (F–I) Schematic of the experiment (F), sample traces (G) and analyses of peak amplitudes (H) and total dopamine (I, quantified as area under the curve) of dopamine release measured in response to puffing of 100 mM KCl onto the recording area. Syt-1 control: n = 7 slices/3 mice, Syt-1 cKODA n = 7/3. All data are shown as mean ± SEM, *p<0.05, ***p<0.001, statistical significance was determined by unpaired t tests in B and C, one-way ANOVA followed by Sidak’s multiple comparisons test in D and E, and Mann-Whitney tests in H and I .