CELLULAR COMPOSITION AND 3-DIMENSIONAL ORGANIZATION OF THE SUBVENTRICULAR GERMINAL ZONE IN THE ADULT MAMMALIAN BRAIN

The adult mammalian subventricular zone (SVZ) contains stem cells that give rise to neurons and glia, in vivo, SVZ progeny migrate 3-8 mm to the olfactory bulb, where they form neurons. We show here that the SV Z of the lateral wall of the lateral ventricles in adult mice is compo sed of neuroblasts, glial cells, and a novel putative precursor cell. The topographical organization of these cells suggests how neurogenesi s and migration are integrated in this region. Type A cells had the ul trastructure of migrating neuronal precursors. These cells were arrang ed as chains parallel to the walls of the ventricle and were polysialy lated neural adhesion cell molecule- (PSA-NCAM), TuJ1- (beta-tubulin), and nestin-positive but GFAP- and vimentin-negative. Chains of Type A cells were ensheathed by two ultrastructurally distinct astrocytes (T ype B1 and B2) that were GFAP-, vimentin-, and nestin-positive but PSA -NCAM- and TuJ1-negative. Type A and B2 (but not BI) cells incorporate d [H-3]thymidine. The most actively dividing cell in the SVZ correspon ded to Type C cells, which had immature ultrastructural characteristic s and were nestin-positive but negative to the other markers. Type C c ells formed focal clusters closely associated with chains of Type A ce lls. Whereas Type C cells were present throughout the SVZ, they were n ot found in the rostral migratory stream that links the SVZ with the o lfactory bulb. These results suggest that chains of migrating neurobla sts in the SVZ may be derived from Type C cells. Our results provide a topographical model for the adult SVZ and should serve as a basis for the in vivo identification of stem cells in the adult mammalian brain .