Proliferative activity and nestin expression in periventricular cells of the adult rat brain.

Mitotic activity in the forebrain subventricular zone is well documented but only in vitro reports suggest the presence of multi-potent stem cells all along the adult mammalian neuraxis. We demonstrate, following cerebroventricular infusion of labeled nucleotides in rat brain, a mitotic activity in the choroid plexus, the ependymal and subependymal layers of the mid- and hindbrain. This proliferation, which probably enables renewal of these structures, was unaffected by the destruction of their serotonergic innervations. Nestin, a marker of immature neural cells, was observed in some proliferative subependymal cells, some classical ependymocytes and in the specialized ependymocytes of the subcommissural organ, the collicular recess and the tanycytes. These observations indicate the presence of immature proliferative cells in the third and fourth periventricular structures, which may generate neural cells.