**1. Introduction**

The treatment of neurological disorders represents a critical issue in clinical research, since no complete recovery of patients can be achieved with actual therapeutic means, despite symptomatic improvements. Indeed, whereas restricted brain areas still house cells compe‐ tent to generate newborn neurons in adulthood, those neural stem cells are present in re‐ stricted amounts. Moreover, this limited neurogenesis does not seem to be sufficient to enable neuronal regeneration in cases of traumatic, ischemic or degenerative lesions of the central nervous system. Therefore, other sources of neural cells have to be considered in a cell therapy objective.

Stem cells are characterized as cells endowed with continuous self-renewal ability and pluri- or multipotentiality, and could consequently give rise to a wide panel of cell types. Non-germinal stem cells are classified into different categories: (1) Embryonic stem cells (ES) are found in the inner cell mass of blastocyst and are pluripotent stem cells that can generate any mature cell of each of the three germ layers; (2) Induced pluripotent stem cells (iPS) are adult somatic cells that are reprogrammed into pluripotent cells with ESlike abilities; (3) Somatic stem cells are tissue-specific and more restricted than ES cells in terms of differentiation capabilities. They can be isolated from various fetal and adult tis‐ sues, which make them an attractive supply of material for cell therapy. Indeed, while neurons have already been successfully generated from ES cells [1] or iPS cells [2, 3], the use of adult somatic stem cells definitely remain of significant interest regarding technical, ethical and immunological issues concerning cell transplantation for brain diseases. In this

© 2013 Neirinckx et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Neirinckx et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

regard, mesenchymal stem cells (MSCs) and neural crest-derived stem cells (NCSCs) that can be found in various locations of the adult organism (and even in perinatal tissues) represent an important source of easily-accessible multipotent cells to use in a cell therapy purpose.

In this chapter, we will describe the major features of MSCs and NCSCs isolated from five different tissues, which constitute the main exploited and accessible sources for cell isolation in an objective of cell therapy protocols for neurological disorders (Figure 1). Moreover, we will detail the multiple ways they can generate neuron-like cells *in vitro*. Indeed, numerous culture conditions and differentiation protocols do exist and are demonstrated as efficient, supporting the fact that neural differentiation can occur through different cellular signaling mechanisms. Therefore, we will review the various signaling pathways that could trigger the neural fate adoption of MSCs and NCSCs, and the related cell-based therapy experi‐ ments that have been done downstream.
