Identification And Characterization Of Neural Progenitor Cells In The Adult Mammalian Brain PDF Download

The fact that the mammalian central nervous system is mostly made up of perennial elements accounting for its well known uncapability to undergo physiological cell renewal and post-lesion repair has represented a dogma for most of the XXth century. Yet, research carried out starting from the sixties in a rather sceptic milieu, and exponentially expanded at the beginning of the nineties with the definitive demonstration that neurogenesis actually takes place in the adult brain and that it is sustained by neural stem cells, opened a new, challenging field in neuroscience. In the last fifteen years, such a field has been tackled by interdisciplinary approaches thus spreading into several ramifications, often referred either more generally to as developmental neurobiology and structural plasticity , or more specifically to as adult neurogenesis . The aims of these studies have become more focused in a wide range of topics, spanning from the detailed morphological/molecular analysis of neurogenic sites to the migration/specification/integration of newlyborn cell precursors into neuronal circuits; from the in vivo identification of cell types and their functional relationships within the neural stem cell niches to the in vitro isolation and characterization of neural stem cells in the perspective of brain repair. In the last few years, in spite of a huge amount of information gathered around the issue of neurogenesis, new elements of complexity have arisen, thus leaving open many questions. It is now clear that persistent neurogenesis do not faithfully reproduce embryonic developmental processes. Indeed, postnatal changes involving the structure/function of neurogenic sites and the neural stem cell niches contained herein, do occur in order to adapt to the mature nervous tissue. The recent finding that adult neural stem cells share a glial identity and directly derive from radial glia raises questions concerning the neuronal-glial relationships across pre- and post-natal development. The progeny of neuronal precursors must integrate into already established neural circuits, whose features change according to the pre- and post-natal developmental stages. In addition, the fact that neural stem cells isolated in vitro prevalently differentiate into astrocytes, whereas in vivo they produce mainly neurons, highlights the importance of epigenetic signals. Finally, substantial data recently obtained under a comparative profile reveal that persistent neurogenesis, although being a well preserved trait, shows remarkable differences among species and, possibly, interesting evolutionary adaptations. The comparative approach, both among mammals and among vertebrates, further reveals new elements of complexity linked to the different growth rates and lifespans. Yet, although introducing new questions about postnatal and adult stages in different species, this approach could provide insights as concerns the functional significance of persistent neurogenesis. Thus, 50 years after the first evidence that new neurons can be generated and added to a mature brain, the actual meaning of such a phenomenon in brain physiology as well as its usefulness in brain repair remain a matter of debate. We learned that neurogenesis can persist in restricted brain sites, whereby it undergoes complex cell/molecular regulation, whereas in the rest of the nervous system it remains as a potentiality. Hence, a better knowledge of the complex regulatory mechanisms underlying these processes should be attained to understand if and how endogenous neurogenesis can be exploited/modulated in the perspective of brain healing. This book, other than providing an overview of the state of the art in the field of postnatal and adult neurogenesis, tries to update our present knowledge about the postnatal changes of neurogenic processes and to place them in the context of a comparative vision. The attainment of this goal has been possible thanks to the contribution of many young scientists from different corners of the world, who have built their experience in neurogenesis during the last decade.