Genetic influence on neurogenesis in the dentate gyrus of adult mice

Abstract

To address genetic influences on hippocampal neurogenesis in adult mice, we compared C57BL/6, BALB/c, CD1(ICR), and 129Sv/J mice to examine proliferation, survival, and differentiation of newborn cells in the dentate gyrus. Proliferation was highest in C57BL/6; the survival rate of newborn cells was highest in CD1. In all strains approximately 60% of surviving newborn cells had a neuronal phenotype, but 129/SvJ produced more astrocytes. Over 6 days C57BL/6 produced 0.36% of their total granule cell number of 239,000 as new neurons, BALB/c 0.30% of 242,000, CD1 (ICR) 0.32% of 351,000, and 129/SvJ 0.16% of 280,000. These results show that different aspects of adult hippocampal neurogenesis are differentially influenced by the genetic background.

Figure 1

Proliferation (A) and survival (B) of cells in the subgranular zone of C57BL/6 mice. BrdU-labeled cells 1 day after the last injection of BrdU (A) have dark irregular shaped nuclei (see Inset). Four weeks later (B) the number of BrdU-positive cells has decreased and the remaining cells have more rounded nuclei, sometimes with the typical chromatin structure of granule cells (see also insert and compare with C–F). Absolute granule cell numbers were determined stereologically using a 15 × 15 μm counting frame superimposed on a video image of Hoechst-33342-stained sections (C–F). No differences in the appearance of the granule cells can be noted, and the neuronal density in the granule cell layer is similar (see Table 2). Phenotypes of surviving newborn cells 4 weeks after the last injection were examined by means of immunofluorescence and confocal microscopy. Cells were categorized as to whether they showed double-labeling for BrdU (green) and granule cell marker calbindin (red) (G), BrdU and astrocytic marker GFAP (blue) (H), or for BrdU and neither of the two other markers (I). Quantification of phenotype distribution is found in Fig. 2B. (Bar in A = 75 μm for A and B and 25 μm for the Insets in A and B.) Counting frames in C–F are 15 × 15 μm. (Bars in G–I = 15 μm.)

Figure 2

Quantification of BrdU-positive cells (A) and phenotype distribution (B). Numbers of BrdU-positive cells were determined 1 day after the last injection to assess proliferative activity (open bars in A) and 4 weeks later to address survival of newborn cells (hatched bars in A). Numbers are totals per granule cell layer (means ± SE). At 4 weeks cells were also examined for the expression of phenotypic marker proteins (B): calbindin for granule cells and GFAP for astrocytes (see Fig. 1 G–I). A total of 50 BrdU-positive cells per animal were analyzed. Statistical analysis is given in Table 1.