Fig. 1. Experimental design. (A) Labeling of newly generated cells was achieved by injecting proliferation marker BrdU into the mice. Cumulative labeling with 12 injections over 12 days leads to a large number of BrdU-positive cells, but results in decreased temporal resolution. A valid estimate of the size of the proliferating population is not possible. (Set 2) To estimate the amount of proliferation at a specific time-point, two single injections of BrdU (6 hours apart) were given to transgenic mice expressing green fluorescent protein (GFP) under the nestin promoter (Yamaguchi et al., 2000). The mice were perfused 24 hours later (see also Table 1). (B) Numbers of BrdU-marked cells were categorized according to their localization in the two blades (dorsal and ventral) of the dentate gyrus in both hemispheres. The underlying image of the mouse brain section is taken from the Mouse Brain Library, section 19 (Rosen et al., 2000), available at http://mickey.utmem.edu/MBL/mbl.html. (C) Numbers of BrdU-marked cells within the GCL were also classified depending on whether they were found in the SGZ plus the inner third of the GCL, or the mid third or the outer third of the GCL. The SGZ was defined as a two-nucleus-wide band below the apparent border between the GCL proper and the hilus.