Figure 5.

Newly born neurons in the subgranular zone-granule cell layer (SGZ-GCL) of different groups, visualized through doublecortin (DCX) immunostaining. The groups include DG of naïve young adult (A1, A2), middle-aged (B1, B2) and aged (C1, C2) hippocampi, and DG of deafferented hippocampi (i.e. hippocampi contralateral to KA) from young adult (D1, D2), middle-aged (E1, E2) and aged (F1, F2) rats at 16 days post-deafferentation. A2, B2, C2, D2, E2, and F2 are magnified views of boxed regions from A1, B1, C1, D1, E1, and F1. Following deafferentation, the density of newly born neurons in the SGZ-GCL increases in the young adult (D1, D2) and middle-aged (E1, E2), in comparison to age-matched naïve rats (A1, A2 and B1, B2). In contrast, the density of newly born neurons is unchanged in the deafferented aged hippocampus (F1, F2), in comparison to the age-matched naïve group (C1, C2). Newly born neurons were observed only occasionally in the dentate hilus of both intact and deafferented hippocampi in all age groups, suggesting that ectopic migration of newly born cells is minimal after deafferentation of the hippocampus. Scale bars, A1, B1, C1, D1, E1, F1 = 200 μm; A2, B2, C2, D2, E2, F2 = 50 μm. The bar chart in G illustrates absolute numbers of newly born neurons (i.e. DCX+ neurons) in the SGZ-GCL of intact and deafferented hippocampi belonging to different age groups. Note that deafferentation considerably enhances the numbers of newly born neurons in the SGZ-GCL of young adult and middle-aged rats but not in aged rats.