Supplementary Figure 6: Estimation of the number of non-reconstructed OB neurons.

(a) Somata near the presumptive caudal boundary of the OB. Colors mark somata of fully reconstructed OB neurons (blue), somata of putative OB neurons (light blue; dendrite directed towards OB), somata of reconstructed cells that do not project into the OB or are not neurons (bright red; non-OB), and somata of putative non-OB cells (pale red; no dendrite towards OB). (b) Number of cells in each class as a function of their minimal distance to an OB neuropil region. Colors as in (a). Light blue line shows an exponential fit to the number of OB neurons as a function of distance. Vertical dashed line shows the distance beyond which no further OB neurons are expected.

In order to estimate the total number of OB neurons we focused on the presumptive boundary of the OB where somata of OB neurons are directly adjacent to, and partially intermingled with, a large number of telencephalic somata. 95 additional candidate cells near the presumptive boundary were reconstructed with redundancy 3. Among these, 21 cells had neurites in the OB and were fully reconstructed using CORE. The remaining cells did not project into the OB or were non-neuronal cells. We observed that primary neurites of OB neurons were always directed towards the OB whereas primary neurites of other neurons pointed in other directions. We used this criterion to estimate the number of OB neurons not included in the set of 1,096 reconstructed neurons. We marked the position of approximately 1,000 additional somata near the presumptive boundary of the OB, determined their distance to the closest neuropil region in the OB, and sorted them into 2.5 μm bins. For all somata up to 20 μm that were not reconstructed before we traced the initial portion of their primary neurite, if any. 24 of these cells were classified as putative OB neurons because they had a primary neurite oriented towards the OB. The number of OB neurons (reconstructed and putative) decreased sharply with increasing distance up to 20 μm (b). An exponential fit predicted that approximately one additional putative OB neuron should be found in subsequent distance bins (≥ 20 μm). We therefore estimate the total number of putative OB neurons that were not included in our reconstructions to be 25. The total number of OB neurons was therefore estimated to be 1,047 (1,001 + 21 + 25). Out of these, 1,022 (98%) were reconstructed by CORE.