Adult Neural Stem/Progenitor Cells in the Forebrain: Implications for Psychostimulant Dependence and Medication

The question as to what exactly a stem cell is has remained contentious even after nearly three decades of debate. The prevailing view is that stem cells are cells with the capacity for unlimited or prolonged self-renewal that can produce at least one type of highly differentiated descendant. Usually, between the stem cell and its terminally differentiated progeny there is an intermediate population of committed progenitors or precursors with limited proliferative capacity and restricted differentiation potential. The term “neural stem cell” is used loosely to describe cells that (1) are derived from the nervous system; (2) have self-renewal capacity; and (3) can give rise to one specific phenotype, or more likely multiple types, of neural cells other than themselves through asymmetric cell division (1 ,2 ). However, to date, it is not clear how primitive the detectable population of dividing cells in the brain is. They may represent true neural stem cells or lineage-restricted progenitor cells. Given this uncertainty, the cautious term “neural progenitor cells” is used in this chapter to describe dividing cells in the central nervous system (CNS).