Following intracardiac perfusion with PBS and 4% paraformaldehyde, the right hippocampus was sectioned into three parts – dorsal, middle and ventral – and fixed overnight in 4% paraformaldehyde at 4°C. The left hippocampus was used for preliminary electrophysiological experiments (not reported here). Serial 30 μm sections of all segments were cut with a vibratome resulting in a total of 200–250 sections per animal. One in ten sections were sampled using a systematic random sampling procedure along the whole dorso-ventral length of the hippocampus. In animals killed at the 90 days time point the sampling frequency was doubled to reach sufficient sampling accuracy. For all groups of animals the criteria for sampling were those outlined by West et al. (1991) and recently reviewed by Wojtowicz and Kee (2006). Thus, for BrdU estimates (the worst case scenario with very few cells to count) in sham control animals for example, CE among the sections was generally below 0.10, while the variance (CV)2 among the animals was always > 0.20. Immunohistochemical procedures for detection of neuronal nucleus (NeuN), doublecortin (DCX), BrdU, and Calbindin (CaBP) were the same as described previously, using the same antibodies from the same suppliers (Wang et al., 2005; Wojtowicz and Kee, 2006). To label for a microglial marker ED1 (CD68) we incubated sections with a primary antibody (mouse, anti-rat, Chemicon) for 24 h at 4°C at 1:200. Washed and incubated with a secondary antibody (goat, IgG, 488 nm, Molecular probes) at 1:200 for 2 hrs at room temperature. A fluorescent marker FluoroJade B (Chemicon) was used to stain for degenerating neurons as described by Schmued and Hopkins (2000).