Hippocampus/embryology; Insulin-Like Growth Factor I/metabolism; Multipotent Stem Cells/metabolism; Neurons/metabolism; Oligodendroglia/metabolism; Stem Cells/metabolism; Animals; Biomarkers; Bone Morphogenetic Proteins/metabolism; Cell Differentiation/drug effects; Cell Differentiation/physiology; Cell Lineage/drug effects; Cell Lineage/physiology; Cells, Cultured; Feedback, Physiological/physiology; Female; Hippocampus/cytology; Hippocampus/metabolism; Insulin-Like Growth Factor I/genetics; Insulin-Like Growth Factor I/pharmacology; Multipotent Stem Cells/cytology; Multipotent Stem Cells/drug effects; Neurons/cytology; Oligodendroglia/cytology; Rats; Rats, Inbred F344; Signal Transduction/physiology; Stem Cells/cytology; Stem Cells/drug effects; Up-Regulation/drug effects; Up-Regulation/genetics