Adult neurogenesis without germinal layers: the "atypical" cerebellum of rabbits.

Unlike non mammalian vertebrates, adult neurogenesis in mammals is detectable in highly restricted brain sites. Persistent neurogenesis is thought to depend on stem cells residing in neural stem cell niches which are remnants of the embryonic germinal layers. Local progenitors which retain some proliferative capacity have been identified in the mature brain parenchyma, yet they do not support a constitutive, 'actual' neurogenesis, but rather a 'potential' neurogenesis which does not extrinsecate fully and spontaneously in vivo. In contrast with such a view, genesis of neuronal and glial cells from local progenitors does occur in the peripuberal and adult rabbit cerebellum. This process is independent from persisting germinal layers and involves different cell populations.