During the last two decades the field of adult neurogenesis has remarkably expanded due to the discovery of neural stem cells in the mammalian central nervous system (CNS), a tissue previously considered as made up of non-renewable elements. The existence of such unexpected plasticity triggered hopes for alternative approaches to brain repair for neurodegenerative diseases. Nevertheless, deeper anatomical, molecular, and functional investigations carried out across these years showed that mammalian neurogenesis persists within two restricted brain regions. These ‘neurogenic sites’ are remnants of embryonic, germinal layers retaining stem/progenitor cells, along with the ‘niche’ environment allowing their activity. Thus, the vast majority of the mammalian CNS, commonly referred to as ‘non-neurogenic parenchyma’, remains as a ‘perennial’ tissue. Recently, some examples of neurogenesis and gliogenesis have been demonstrated to occur even in parenchymal regions, although with different intensity and outcomes with respect to typical neurogenic sites. In other classes of vertebrates including fish, amphibians, and reptiles, adult neurogenesis is widespread in the parenchyma, also intervening in brain repair and regeneration. By contrast, in birds and mammals this process is progressively restricted to specific systems and exclusively aimed at their physiology/homeostasis. Thus, out of the neurogenic regions other types of plasticity prevail (e.g., synaptic plasticity) and neurogenesis seems a remnant of an ancestral ability with no evident roles in parenchymal homeostasis/repair. Nevertheless, before definitively move to other directions in search for ways to replace the lost neural elements in the adult CNS, it is worth to further explore the true potential of mammalian parenchymal stem/progenitor cells in physiological state and in diverse pathological conditions. Finally, an open field of research could be that trying to find how these two aspects of CNS plasticity, i.e. compensatory plasticity of pre-existing neuronal structures and newly generated parenchymal cells, could be complementary each other, and affected/modulated after injury.
New research perspectives in Mammalian parenchymal neurogenesis
BONFANTI, Luca;PERETTO, Paolo Marcello
2012-01-01
Abstract
During the last two decades the field of adult neurogenesis has remarkably expanded due to the discovery of neural stem cells in the mammalian central nervous system (CNS), a tissue previously considered as made up of non-renewable elements. The existence of such unexpected plasticity triggered hopes for alternative approaches to brain repair for neurodegenerative diseases. Nevertheless, deeper anatomical, molecular, and functional investigations carried out across these years showed that mammalian neurogenesis persists within two restricted brain regions. These ‘neurogenic sites’ are remnants of embryonic, germinal layers retaining stem/progenitor cells, along with the ‘niche’ environment allowing their activity. Thus, the vast majority of the mammalian CNS, commonly referred to as ‘non-neurogenic parenchyma’, remains as a ‘perennial’ tissue. Recently, some examples of neurogenesis and gliogenesis have been demonstrated to occur even in parenchymal regions, although with different intensity and outcomes with respect to typical neurogenic sites. In other classes of vertebrates including fish, amphibians, and reptiles, adult neurogenesis is widespread in the parenchyma, also intervening in brain repair and regeneration. By contrast, in birds and mammals this process is progressively restricted to specific systems and exclusively aimed at their physiology/homeostasis. Thus, out of the neurogenic regions other types of plasticity prevail (e.g., synaptic plasticity) and neurogenesis seems a remnant of an ancestral ability with no evident roles in parenchymal homeostasis/repair. Nevertheless, before definitively move to other directions in search for ways to replace the lost neural elements in the adult CNS, it is worth to further explore the true potential of mammalian parenchymal stem/progenitor cells in physiological state and in diverse pathological conditions. Finally, an open field of research could be that trying to find how these two aspects of CNS plasticity, i.e. compensatory plasticity of pre-existing neuronal structures and newly generated parenchymal cells, could be complementary each other, and affected/modulated after injury.
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