Neurogenesis Outside the Central Nervous System (An Overview)

Adult neurogenesis in the mammalian central nervous system is restricted to small, embryonic germinal layer-derived neurogenic sites localized in the forebrain. This neurogenic process is sustained throughout life by neural stem cells harboured within wel

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Luca Bonfanti and Paola Crociara

Contents

Abstract

Introduction ............................................................

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Olfactory Mucosa ...................................................

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Retina ...................................................................

274

Enteric Nervous System.........................................

275

Carotid Body ..........................................................

276

Taste Buds ...............................................................

277

Sensory Ganglia .....................................................

278

References ...............................................................

279

Adult neurogenesis in the mammalian central nervous system is restricted to small, embryonic germinal layer-derived neurogenic sites localized in the forebrain. This neurogenic process is sustained throughout life by neural stem cells harboured within well characterized niches. Persistent neurogenesis is also known to occur in various organs of the peripheral nervous system, (e.g., retina, olfactory mucosa, gut, and carotic body). Ongoing research is trying to describe the atypical niches in which different types of new neurons are produced, with the aim of unraveling the mechanisms which regulate them at different locations.

Introduction

L. Bonfanti (*) • P. Crociara Neuroscience Institute Cavalieri Ottolenghi (NICO), University of Turin, Turin, Italy e-mail: [email protected]

Adult neurogenesis, namely the capacity of generating new nerve and glial cells throughout life, is a phylogenetically highly conserved feature that challenges the dogma of the nervous system as a static, non-renewable tissue. In invertebrates and non-mammalian vertebrates, neurogenesis persists in wide regions of the central nervous system (CNS). In adult mammals, as reviewed in Gage (2000) and Kriegstein and Alvarez-Buylla (2009), a ‘constitutive’ genesis of new neurons is mainly restricted to two brain sites: the forebrain subventricular zone and the

M.A. Hayat (ed.), Tumors of the Central Nervous System, Volume 9, DOI 10.1007/978-94-007-5488-1_30, © Springer Science+Business Media Dordrecht 2012

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hippocampal dentate gyrus. The persistence of neurogenesis in these zones depends on stem cells which reside in niches as vestigial remnants of embryonic germinal layers. To a lesser extent, it has been demonstrated to occur even in humans, and recently, neurogenic/gliogenic processes have been shown to exist also in the brain parenchyma of some mammals. This ‘parenchymal’, non-constitutive cell genesis starts from local progenitor cells not performing as true stem cells, yet further studies are needed to ascertain their real potentialities. In the last few years, in parallel with intense research on brain neurogenesis, evidence has been accumulated that new neurons can also be produced at several locations outside the CNS. Among these regions, the olfactory mucosa is known since long time, far before the demonstration of adult CNS neurogenesis. More recently