ARCHITECTURE AND CELL-TYPES OF THE ADULT SUBVENTRICULAR ZONE - IN SEARCH OF THE STEM-CELLS

Neural stem cells are maintained in the subventricular zone (SVZ) of t he adult mammalian brain. Here, we review the cellular organization of this germinal layer and propose lineage relationships of the three ma in cell types found in this area. The majority of cells in the adult S VZ are migrating neuroblasts (type A cells) that continue to prolifera te. These cells form an extensive network of tangentially oriented pat hways throughout the lateral wall of the lateral ventricle, Type A cel ls move long distances through this network at high speeds by means of chain migration. Cells in the SVZ network enter the rostral migratory stream (RR;IS) and migrate anteriorly into the olfactory bulb, where they differentiate into interneurons. The chains of type A cells are e nsheathed by slowly proliferating astrocytes (type B cells), the secon d most common cell type in this germinal layer. The most actively prol iferating cells in the SVZ, type C, form small clusters dispersed thro ughout the network. These foci of proliferating type C cells are in cl ose proximity to chains of type A cells, We discuss possible lineage r elationships among these cells and hypothesize which are the neural st em cells in the adult SVZ, In addition, we suggest that interactions b etween type A, B, and C cells may regulate proliferation and initial d ifferentiation within this germinal layer. (C) 1998 John Wiley & Sons, Inc.