Since reports that precursor cells in the adult subventricular zone (SVZ) 
contribute to regenerative neuro- and gliogenesis in CA1, we wondered whether a 
similar route of migration might also exist under physiological conditions. 
Permanent labeling of SVZ precursor cells with a lentiviral vector for green 
fluorescent protein did not reveal any migration from the SVZ into CA1 in the 
intact murine brain. However, in a nestin-GFP reporter mouse we found 
proliferating cells within the corpus callosum/alveus region expressing nestin 
and glial fibrillary acidic protein similar to precursor cells in the 
neighboring neurogenic region of the adult dentate gyrus. Within 3 weeks of BrdU 
administration, BrdU-positive nestin-GFP-expressing protoplasmic astrocytes 
emerged in CA1. Similar to precursor cells isolated from the dentate gyrus and 
the SVZ, nestin-GFP-expressing cells from corpus callosum/alveus were 
self-renewing and multipotent in vitro, whereas cells isolated from CA1 were 
not. Nestin-GFP-expressing cells in CA1 differentiated into postmitotic 
astrocytes characterized by S100beta expression. No new neurons were found in 
CA1. The number of nestin-GFP-expressing astrocytes in CA1 was increased by 
environmental enrichment. We conclude that astrogenesis in CA1 is influenced by 
environmental conditions. However, SVZ precursor cells do not contribute to 
physiological cellular plasticity in CA1.