Aging, Animals, Cell Differentiation, Cell Lineage, DNA-Binding Proteins, Flow Cytometry, Gene Expression Profiling, Gene Expression Regulation, Developmental, Genetic Markers, Globus Pallidus, Mice, Mice, Inbred C57BL, Mice, Transgenic, Neostriatum, Neural Pathways, Neurons, Oligonucleotide Array Sequence Analysis, RNA, Messenger, Substantia Nigra, Trans-Activators