Neuronal differentiation is significantly decreased by age in the mouse hippocampal DG.

<p>POMC-EGFP-expressing mice were sacrificed at 1, 1.5, 2, 2.5, 3, 4, 6, 12, 18, 24 months of age by transcardial perfusion and their brains were processed for immunohistochemistry for the immature neuronal marker NeuroD (A-C) and visualized for the expression of EGFP (D-F). Age induced a significant decline in the expression of both NeuroD (A-C) and EGFP (D-F). An abrupt reduction in neuronal differentiation was detected early on (between 1.5 and 3 months of age) with both markers. Data are presented as means ± SEM. (A) *** <i>p</i> < 0.001 between 1 or 1.5 and 2 months, between 2 and 4 months, between 4 and 12 months, and between 6 and 18 or 24 months. (D) ** <i>p</i> < 0.01 between 4 and 12, 18, or 24 months, *** <i>p</i> < 0.001 between 1 or 1.5 and 2 months, and between 2 and 4 months. See text for additional statistical details. Representative sections of the DG processed for NeuroD immunohistochemistry (B, C) and analyzed for EGFP expression (E, F) in 1- (B, E) and 24- (C, F) month old POMC-EGFP mice. Arrows indicate a NeuroD-immunopositive cell (C) and an EGFP-expressing cell (F) in the DG of a 24-month old mouse. Scale bars (B, C) = 100 µm; scale bars (E, F) = 50 µm.