The putative neural stem cell marker, nestin, is expressed in heterogeneous cell types in the adult rat neocortex

Nestin is a putative neural stem cell marker that is expressed in different areas of the adult mammalian brain that are known to support mitotic activity. Recently the neocortex has been proposed to support neurogenesis, however little is known of the expression pattern of nestin in neocortex. In the present study, we demonstrate that cells that express nestin can be found throughout the neocortex, and that these cells are morphologically heterogeneous. Some nestin-expressing cells had one extension arising from the cell body, reminiscent of the nestin-expressing cells that are thought to be young neurons in the hippocampus. The frequency of single extension cells in the neocortex was approximately one cell per 50,000 microm(2). Other cells had numerous extensions arising from the cell body. In all cases, cells that expressed nestin were also found to co-label with the glial marker glial fibrillary acidic protein. In addition, nestin-expressing cells in the neocortex did not express the cell cycle marker, Ki-67, indicating they were not actively engaged in mitotic activity. When small lesions were made in cortex, nestin could also be observed in reactive astrocytes as part of the inflammatory response. Approximately 94% of reactive astrocytes expressed Ki-67. These results demonstrate that there are different populations of cells in the neocortex that can express nestin, but that only reactive astrocytes in this region are mitotically active.