Figure 8.

Serial section EM and EM tomography reveals similar densities of docked vesicles in AZs innervating O-LM and FSINs

(A and B) High magnification electron micrographs of 20-nm-thick sections showing excitatory synapses on an FSIN (A, orange) and an O-LM IN (B, cyan) dendrite. Arrowheads demarcate the edges of the synapses; arrows point to docked vesicles.

(C) Docked vesicles have similar densities in AZs reconstructed from serial 20-nm-thick sections that innervate FSIN and O-LM cell dendrites (p = 0.9, MWU test, n = 15 and 21 synapses in 1 mouse).

(D and E) Electron tomographic subvolumes (0.6 nm thick) of representative excitatory synapses on an FSIN (D, orange) and O-LM IN (E, cyan) dendrite. Arrowheads demarcate the edges of the synapses; arrows point to docked vesicles.

(F) Docked vesicles have similar densities in AZs innervating FSIN and O-LM cell dendrites (p = 0.16, MWU test, n = 68 FSIN and 63 O-LM cell targeting synapses in 4 mice). Densities were calculated from 200-nm-thick sections. Filled circles represent means within individual cells. Horizontal lines in the boxplots: 25th, 50th, and 75th percentiles, rectangle: mean, whiskers: SD.

(G) Spatial distribution of vesicles within 100 nm of the AZ membrane. Inset shows the spatial distribution within the first 30 nm (n = 20 FSIN and 30 O-LM cell targeting synapses in 3 mice). Data are shown as mean ± SD.

(H) Number (mean ± SD) of vesicles within bins of 5 and 10 nm distance from the AZ normalized to AZ area (n = 20 FSIN and 30 O-LM cell targeting synapses in 3 mice).