Cell Proliferation Dynamics in Lizard Telencephalon

To assess the distribution of proliferating cells in the VZ, lizards injected with [³H]-thymidine with a survival time of 1.5 h were used (n = 5). The VZ was divided in six different regions, including three sulcal zones (sulcus medalis, sulcus lateralis and sulcus ventralis/terminalis) and three intersulcal zones (intersulcus corticalis, intersulcus lateralis, and intersulcus septalis) (Figure 1B). The number of [³H]-thymidine labeled cells was counted in all these regions relative to the total number of cells. This quantification was performed in two telencephalic levels: one pre-commissural (anterior) and one post-commissural (posterior), analyzing for each level a total of 7 semithin sections which were 9 μm apart to avoid counting the same cell twice. Different types of counts were performed by quantifying the total number of labeled cells/1000 cells considering sulci vs. intersulcal regions, comparing between the different sulci and intersulcal regions and differentiating between the pre- and post-commissural levels for each animal.
To characterize the ultrastructure of VZ proliferative cells and their derivatives, the brains of specimens with 1.5, 6, 12, 24, and 72 h survival times were examined. Between 50 and 150 [³H]-thymidine-positive ([³H]-thy⁺) cells were analyzed for each survival time, including at least two different antero-posterior levels per lizard. These cells were studied by transmission electron microscopy (TEM) to determine their ultrastructural characteristics. Counts were also made of the number of cells in mitosis (M phase) labeled relative to the total number of [³H]-thy⁺ cells.
The analysis of specimens with long survival times (1, 3, 6, and 12 months) focused mainly on the cell layer of the MC, although we also investigated whether there were labeled cells in the walls of the LVs. Within the MC we analyzed the ultrastructure of 25–50 [³H]-thy⁺ cells from each survival time to see to which neuronal type they corresponded.