Adult neurogenesis and local neuronal progenitors in the striatum.

Mechanisms underlying neurogenesis in the subventricular-zone-olfactory-bulb system and dentate gyrus of the hippocampus are beginning to be delineated and show common regulative features. In both regions neurogenesis is attributable to progenitor cells whose progeny progressively matures to functional neurons under genetic and epigenetic influence. Persistence of endogenous neuronal progenitors and integration of new neurons in preexisting circuits provide an appealing model of study to develop therapy strategies for neurodegenerative diseases. Interestingly, comparative analysis in mammals indicates that low neurogenic activity is also present in regions classically considered nonneurogenic in both normal and pathological conditions. Neurogenesis in these regions can be due to progenitors derived from the subventricular germinal zone and/or local parenchymal progenitors. Although, in vivo, the origin, identity and putative function of parenchymal progenitors are still obscure, in vitro studies suggest that many regions of the adult central nervous system potentially contain multipotent parenchymal progenitors. The aim of this review is to delineate the common regulative features underlying adult neurogenesis in the main neurogenic regions and in the striatum focusing on our recent data concerning the existence of local parenchymal progenitors in the caudate nucleus of the adult rabbit.