Historical Perspective

It took several decades to agree that new neurons are generated in adult brain but less time to establish that they are functionally integrated in two discrete regions: the olfactory bulb (OB) and the hippocampus (Ming and Song 2005; Lledo et al. 2006; Zhao et al. 2008). While our current knowledge on adult neurogenesis in mammals is mainly based on rodent studies, recent in vivo data have confirmed the occurrence of neural stem cells in the human brain (Manganas et al. 2007), already detected in postmortem tissues (Eriksson et al. 1998). Originally described by Altman (Altman 1969) using [3H]thymidine autoradiography, the presence of new neural cells in adult brain was rediscovered by Gould et al. in the early 1990s (Gould et al. 1992; Cameron et al. 1993) in studies based on the administration of 5-bromo-2'-deoxyuridine (BrdU), a thymidine analogue taken up by cells synthesizing DNA in preparation for division. BrdU-labeled neurons are visualized using a method, immunocytochemistry, which can be combined with or used in parallel with several other techniques or models, including novel transgenic mouse lines (Yamaguchi et al. 2000; Encinas and Enikolopov 2008). Together, these tools allow the visualization of discrete stages of neurogenesis and ascertain the neuronal identity of the new cells. Indeed, the term neurogenesis refers to the combined processes of cell proliferation, survival, differentiation, maturation, and synaptic integration in the preexisting circuitry (Duan et al. 2008). Adult neurogenesis thus appears to be an extreme form of structural remodeling, compared with the subtle modification in synaptic morphology mediating functional plasticity of neural circuitry. Furthermore, numerous factors can modulate the number of newborn cells, suggesting that adult neurogenesis represents an adaptive response to various challenges imposed by an external and/or internal environment, under physiological or pathological conditions.

IBDML, UMR 6216, CNRS, Marseille, France e-mail: [email protected]

G. Di Giovanni et al. (eds.), 5-HT2C Receptors in the Pathophysiology of CNS Disease, 169

The Receptors 22, DOI 10.1007/978-1-60761-941-3_9, © Springer Science+Business Media, LLC 2011

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