Figure 2. Neural cell type proportions and DNA content in the vital fraction of cortical cell isolates as a function of age. (A) Cellular entities were identified by applying cell type-specific markers, using ßIII-tubulin, S100-ß, Iba-1 and CA-II for neurons, astrocytes, microglia and oligodendrocytes, respectively, with cell nuclei being discriminated by DAPI. Scale bar, 5 µm. (B) Cell type-specific proportions did not vary between young and aged mice. NEU, neurons; MG, microglia; OGD, oligodendrocytes; AST, astrocytes. Bars represent means ± SEM (n = 500 cells out of 3 animals per condition). (C and D) Representative DNA histograms illustrating an age-associated shift in cell cycle activity, as assessed by PI staining of DNA from murine cortical neural cell isolates at an age of 3 months (C) and 25-27 months (D). (E) Neocortical cell constituents derived from aged animals showed a shift towards replicative cell cycle phases, marked by a significant increase in the proportion of cells in S, G2/M and >G2 phase, whereas the percentage of cells in G0/G1 phase declined significantly at higher age. Bars represent means ± SEM (n = 4 - 8). For (B and E) P-values were calculated using the Student’s t-test.