ABSTRACT
The concept of a stem cell whose properties include the ability to give rise to a multitude of cell types and to self-renew, has been well established in many systems, particularly the haematopoietic system, and yet only recently has it been deemed applicable to the central nervous system. This was partly because of the inability to grow stem cells in vitro or to monitor their progeny in vivo, but a more important impediment to the acceptance of the stem cell concept has been the unwillingness to embrace the property of self-renewal, mainly because this implied an ongoing presence of stem cells in the mature nervous system.
