Figure 5

Two weeks after BrdU labeling, new cells have migrated and differentiated into neurons and a few new cells are retained in the ventricular zone and express GFAP. (A) Confocal image at 10× magnification shows that, in the uninjured axolotl telencephalon, most BrdU⁺ cells have migrated into the mantle zone 2 weeks after labeling. A few BrdU⁺ cells are retained in the VZ. (B,C) Confocal images taken at 40× objective (2.3× digital zoom) of sections stained with 4^′-6-diamidino-2-phenylindole (in white; B₁ and C₁) and antibodies against (B) BrdU (in red; B₂) and GFAP (in green; B₃) or (C) BrdU (in red; C₂), DCX (in blue; C₃), NeuN (in green; C₃). The image in (B) shows that very few BrdU⁺ cells are retained in the VZ by 2 weeks after overnight BrdU labeling, but those that do remain and express GFAP may represent new radial glia-like cells. (C) by 2 weeks, all BrdU⁺ cells in the mantle zone express the mature neuronal marker NeuN (white and yellow arrows) and a small percentage of the NeuN⁺ neurons retain DCX expression (yellow arrows) and are likely transitioning into mature neurons. (D) The relatively small densities (versus F) of BrdU/GFAP⁺ cells retained in the VZ are resilient across weeks 2 to 4 after BrdU labeling. (E) Most BrdU⁺ VZ cells express GFAP. (F) All BrdU⁺ cells in the neuronal layer express NeuN and a few NeuN⁺ neurons retain DCX expression. These percentages are consistent across weeks 2 to 4 after BrdU labeling. (G) New neurons are either vulnerable to cell death or are still migrating because their densities significantly decrease between weeks 2 and 3 (**P <0.001). BrdU: bromodeoxyuridine; DCX: doublecortin; GFAP: glial fibrillary acidic protein; VZ: ventricular zone.