Fig. 4. The effect of HDACIs on the survival of newborn neurons is limited in a specific time window. (A) A schematic paradigm for the time-specific effect of VPA and SBt on the survival of newborn neurons. VPA was injected for 14 days, either 2 or 4 weeks after BrdU injection. (B) The number of BrdU(+) cells was increased by VPA treatment when treated 2 weeks after the BrdU injection. VPA treatment 4 weeks after the BrdU injection was not effective on the survival of newborn neurons. (C) Double-labeled images for BrdU (red) and NeuN (green). The increased number of BrdU and NeuN labeled cells (BrdU⁺NeuN⁺; arrows) in VPA treated group is significantly distinct 2-3 week treatment after BrdU injection, not in 4-5 week time point. (D) Values are shown as an averaged number of BrdU⁺NeuN⁺ cells/mm³ ± SEM. *p < 0.05, Student’s t-test.