This volume is based on a meeting of the Fondation IPSEN, held in Paris
on Sep- tember 18, 1995 to address the main issues of nervous system
stem cells biology. Cell replacement in the adult mammals is not unusual
outside the nervous sys- tem. In fact, the nervous system is unique in
lacking the ability to replace cells, following damage. Most neurons, in
the adult central nervous system are termin- of the organism and are not
replaced ally differentiated, exist through the life when they die.
There are, however, regions of the postnatal brain that continue to
produce new neurons, but the fate and longevity of those cells are not
well known. Evidence exists that small populations of neurons continue
to be born in the adult ventricular zone, olfactory epithelium and
hippocampus. In the adult hippocampus, newly born neurons originate from
putative stem cells that exist in the sub granular zone of the dentate
gyrus. Progeny of these putative stem cells differentiate into neurons
in the granular layer within a month of the cells' birth, and this late
neurogenesis continues throughout the adult life of the rodent. By
understanding the nature of progenitor cells present in the embryonic
and adult brains, the change in their population dynamics during
development, and the factors that influence their proliferation, fate
choice and differentiation, it may be possible to develop a strategy to
manipulate cells in situ to treat neuro- degenerative diseases or the
injured adult brain.