Number and subcellular placement of synapses between neocortical interneurons
| Connection | BC to BC | BC to DTC | BC to DBC | DBC to BC |
|---|---|---|---|---|
| Number of connections studied | ||||
| Light and electron microscopy | 3 | 1 | 3 | 3 |
| Synaptic effect recorded | 2 | 1 | 2 | |
| Light microscopic prediction | ||||
| Number of close appositions | ||||
| On the soma | 1.3 ± 0.6 | 1 | 0.3 ± 0.6 | 0.0 ± 0.0 |
| On dendrites | 6.7 ± 4.6 | 0 | 3.7 ± 1.5 | 4.3 ± 3.2 |
| Total | 8.0 ± 4.4 | 1 | 4.0 ± 1.7 | 4.3 ± 3.2 |
| Electron microscopic verification | ||||
| Number of synapses | ||||
| On the soma | 5.0 ± 3.6 | 2 | 0 | 0 |
| On dendrites | 7.3 ± 3.2 | 0 | 1.7 ± 0.6 | 3.0 ± 1.7 |
| Total | 12.3 ± 6.8 | 2 | 1.7 ± 0.6 | 3.0 ± 1.7 |
| % of light microscopic prediction | ||||
| On the soma | 433.3 ± 404.1 | 200 | ||
| On dendrites | 122.3 ± 29.3 | 55.0 ± 39.7 | 77.8 ± 48.1 | |
| Total | 153.5 ± 13.3 | 200 | 53.3 ± 41.6 | 77.8 ± 48.1 |
| Distance from the soma (μm)* | 15.8 ± 12.4 | 0 | 25.7 ± 18.9 | 42.9 ± 19.2 |
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The complete dendritic arborizations of all cells were checked in the light microscope. All light microscopically observed close appositions of neural processes were electron microscopically tested in serial sections. Because of the limited resolution and the strongly filled cell bodies obscuring thin axonal processes, light microscopic predictions proved highly unreliable. Basket cells established synaptic junctions closer to the somata of postsynaptic neurons than did DBCs (p < 0.0005). The number of synapses between BCs was higher than in BC-to-DBC and DBC-to-BC connections (p < 0.05).
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* Measured as a two-dimensional projected distance.
