Review : Neuronal Precursor Cells and Neurogenesis in the Adult Forebrain

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Abstract
Neuronal precursor cells persist in the forebrain of a wide variety of adult vertebrates and have been found in cultures derived from fish, birds, rodents, and humans. These cells reside within the periventricular epen dymal/subependymal zone (SZ), rather than the brain parenchyma. In vivo, these precursors may generate neurons that are recruited to restricted regions, such as the avian neostriatum and mammalian olfactory bulb. In vitro, however, neuronal precursor cells have been found to be distributed more widely than suggested by the limited distribution of adult neurogenesis in vivo; in the adult rat brain, new neurons arise from SZ explants derived from most of the surface of the lateral ventricular system. In primates, although the postnatal forebrain SZ largely ceases neurogenesis in vivo, it too retains the capacity for neuronal production in vitro, as dem onstrated in explants of adult human temporal lobe SZ. In mammals, the division of these precursor cells may be regulated by both epidermal and fibroblast growth factors, whereas the survival of their neuronal progeny is regulated in part by members of the neurotrophin family, specifically BDNF and NT-4. Together, these findings suggest the persistence into adulthood of a relatively widespread pool of SZ progenitor cells, which remains neurogenic in selected regions, but which more generally becomes vestigial, perhaps as a result of the loss of permissive signals for daughter cell migration or survival in the local environment. The Neuroscientist 1:338-350, 1995