Nestin expression and in vivo proliferative potential of tanycytes and ependymal cells lining the walls of the third ventricle in the adult rat brain.

There is a disagreement in the literature concerning the degree of proliferation of cells in the walls of the third ventricle (3rdV) under normal conditions in the adult mammalian brain. To address this issue, we mapped the cells expressing the neural stem/progenitor cell marker nestin along the entire rostrocaudal extent of the 3rdV in adult male rats and observed a complex distribution. Abundant nestin was present in tanycyte cell bodies and processes and also was observed in patches of ependymal cells as well as in isolated ependymal cells throughout the walls of the 3rdV. However, we observed very limited ependymal cell or tanycyte proliferation in normal adult rats as determined by bromodeoxyuridine (BrdU) incorporation or the expression of Ki-67. Moreover, fewer than 13% of the cells that were BrdU-positive (BrdU+) or Ki-67-positive (Ki-67+) expressed nestin. These observations stand in contrast to those made in the subventricular zone of the lateral ventricle (SVZ) and subgranular zone of the hippocampal formation (SGZ), where cell proliferation measured by BrdU incorporation or Ki-67 expression is observed frequently in cells that also express nestin. Thus, while ependymal cell or tanycyte cell proliferation can be promoted by the addition of mitogens, dietary modifications or other in vivo manipulations, the proliferation of ependymal cells and tanycytes in the walls of the 3rdV is very limited in the normal adult male rat brain.