TABLE 1.
Comparison of Measurements for High-SR versus low-SR synapses1
| Feature | High-SR synapse | Low-SR synapse | High/Low ratio |
|---|---|---|---|
| Synaptic ribbon | |||
| Length (nm) | 245 (30) | 338(38) | 0.72 |
| Width (nm) | 86.1 (4.4) | 84.8 (5.1) | 1.02 |
| Height (nm) | 150.7 (13.6) | 135.4 (3.7) | 1.11 |
| Volume (nm3) | 3,139,274 (96,681) | 3,267,930 (196,015) | 0.96 |
| Surface area (nm2) | 119,198 (5,377) | 138,034 (12,444) | 0.86 |
| Synaptic densities | |||
| Active zone area (nm2) | 310,371 (24,735) | 377,186 (63,181) | 0.82 |
| Active zone length (nm/section) | 752 (22) | 705 (22) | |
| Presynaptic density length (nm/section) | 799 (37) | 741 (29) | |
| Postsynaptic density length (nm/section) | 794 (39) | 724 (32) | |
| Presynaptic area beneath ribbon (nm2) | 56,350 (5,499) | 77,817 (8,736) | 0.72 |
| Vesicles on ribbon surface | |||
| No. excluding immediately releasable pool | 34.7 (3.3) | 39.3 (6.6) | 0.88 |
| No. including immediately releasable pool | 42.8 (3.3) | 51.3 (8.3) | 0.83 |
| Density including immediately releasable pool (/μm2) | 362.9 (30.6) | 360.8 (33.7) | 1 |
| Vesicles docked on the presynaptic density | |||
| No. | 44.2 (6.1) | 56.9 (10.1) | 0.77 |
| Density (/μm2) | 145.2 (20.9) | 157.6 (18.2) | 0.92 |
| Vesicles beneath ribbon (immediately releasable pool) | |||
| No. | 8.2 (1.1) | 12 (1.8) | 0.68 |
| Density (/μm2) | 149.8 (25.4) | 153 (14.8) | 0.98 |
| Vesicles in the proximal free pool* (P =0.015) | 78.5 (7.8) | 109.7 (7.4) | 0.72 |
| Vesicles (% total area) | 7.34 (0.66) | 7.90 (0.20) | 0.93 |
| Cisterns (% total area) | 8.36 (1.00) | 10.71 (1.15) | 0.78 |
| Average mitochondrial content of afferent fibers* (P =0.001) | 1.68 (0.07) | 0.69 (0.04) | 2.42 |
1
Standard error (SE) is in parentheses. SR, spontaneous rate.
*
Significant differences between low- and high-SR synapses.