Impaired morphological development of new granule neurons in 3 month-old Tg2576 mice.

<p>(A) Confocal images (left) illustrating typical retrovirally GFP-labeled (GFP+, green) neurons 28 days post-injection (dpi) in the dentate gyrus of 3 month-old NTg and Tg2576 mice (neuronal marker NeuN, red) and their corresponding 3D reconstruction (right) illustrating the arborization and branching points of GFP+ neurons. (B) No difference was found in the total dendritic length of GFP+ neurons from NTg and Tg2576 mice (n=3-6 mice/group and 15-20 GFP+ cells/group). (C) The length of the primary dendrite was measured as indicated in inset. At 28dpi GFP+ neurons in Tg2576 mice exhibited a shorter primary dendrite compared to NTg mice (n=3-4 mice/group, n=20-25 GFP+ cells/group). (D) Number of branching points was counted in 14 and 28dpi GFP+ neurons (n=3-4 mice/group, 20-25 GFP+ cells/group). At 28dpi, GFP+ neurons exhibited less branching points in Tg2576 mice compared to NTg mice. (E) Maximal dendritic length of GFP+ neurons as quantified as illustrated in inset. At 28dpi, Tg2576 mice displayed shorter maximal dendritic length compared to NTg (n=3-4 mice/group and n=20-25 GFP+ cells/group). (F) Maximal projection of z-stacks confocal images illustrating dendritic segments from 28dpi GFP+ neurons, from which dendritic spines were counted and classified as stubby (S), filopodia (F), thin (T) or mushroom (M) according to morphological criteria described in the methods. (G) Spine density estimated from 28dpi GFP+ neurons (n=3 mice/group, 4-8 segments/mouse, 200-300µm of dendritic segments analyzed/mouse) was reduced in 3 month-old Tg2576 mice compared to NTg. (H) Among all classes, the density of thin spines was reduced in Tg2576 mice compared to NTg. (I) Confocal image depicting mature neurons (NeuN, red) and 28 day-old new neurons (GFP, green) in the dentate gyrus. Axons of GFP+ neurons (arrow) extending into the CA3 region are clearly visible, allowing the measurement of axonal length. (J) At 28dpi, axons of GFP+ neurons appeared shorter in Tg2576 compared to NTg mice. Data in B, C, D, E, G, H, J represent mean ± SEM. Data were analyzed by two-way ANOVA with Bonferroni post-hoc: *p<0.05; ***p<0.001 Tg2576 <i>vs</i> NTg. Scale bars: A (left)=50µm, (right)=30µm F=2µm, I=500µm.