Hippocampal injury leads to increased addition of new neurons to the dentate granule cell layer (GCL) in the adult hippocampus but not in the middle-aged and the aged hippocampus (Rao et al., SFN Abstracts, 2003). We hypothesize that age-related malfunction in the response of dentate neurogenesis to hippocampal injury is owed to insufficient concentration of stem/progenitor cell proliferation factor FGF-2 in the injured aging hippocampus. To address this issue, we determined the number of new cells and neurons in the subgranular zone (SGZ) and GCL of the injured hippocampus of 24-months-old F344 rats following subcutaneous administration of fibroblast growth factor-2 (FGF-2). The hippocampal lesion was induced through an intracerebroventricular kainic acid administration, and FGF-2 was administered via daily subcutaneous injections between post-lesion days 4 and 15. The new cells and neurons that were born during FGF-2 administration were labeled using daily intraperitoneal injections of 5’-bromodeoxyuridi...