FIGURE 1.

Aged NPCs have a lower proliferative index. Cells were plated at serial dilutions in 96-well plates. After 1 week, neurospheres were quantified. A, NPCs derived from the young adult forebrain produced more neurospheres at nearly every plating dilution compared with those from the aged adult forebrain (p < 0.01, linear regression analysis; error bars, S.E.). B, aged cells produced more wells with no spheres at each dilution (B, p < 0.01, linear regression analysis). C–H, cultures from the young adult (C–E) and aged adult brain (F–H) are shown, after 1 week, at original plating dilutions of 25 cells (C and F), 250 cells (D and G), and 1000 cells (E and H). I, aged cells incorporate significantly less of the thymidine analog IdU during a 30-min pulse compared with young cells (p < 0.05). J and K, pictured are young (J) and aged (K) NPCs labeled with the nuclear marker DAPI (blue) and IdU (red). Scale bars, 10 μm.