Is integration and survival of newborn neurons the bottleneck for effective neural repair by endogenous neural precursor cells?

They ask a great question.  
Who is being given the task to answer it? Shit, no one will, it will just drop by the wayside like all the other promising stroke questions.
http://journal.frontiersin.org/Journal/10.3389/fnins.2014.00029/full?
Ann M. Turnley*, Harleen S. Basrai and Kimberly J. Christie

    Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, VIC, Australia

After two decades of research the existence of adult neural precursor cells and the phenomenon of adult neurogenesis is well established. However, there has been little or no effective harnessing of these endogenous cells to promote functional neuronal replacement following neural injury or disease. Neural precursor cells can respond to neural damage by proliferating, migrating to the site of injury, and differentiating into neuronal or glial lineages. However, after a month or so, very few or no newborn neurons can be detected, suggesting that even though neuroblasts are generated, they generally fail to survive as mature neurons and contribute to the local circuitry. Is this lack of survival and integration one of the major bottlenecks that inhibits effective neuronal replacement and subsequent repair of the nervous system following injury or disease? In this perspective article the possibility that this bottleneck can be targeted to enhance the integration and subsequent survival of newborn neurons will be explored and will suggest some possible mechanisms that may need to be modulated for this to occur.
 
Introduction

Two decades of research has demonstrated that a surprisingly wide variety of factors can influence adult neural precursor cell biology (Christie and Turnley, 2012). This includes extrinsic factors, such as growth factors, cytokines, chemokines, neurotrophins, steroids and extracellular matrix molecules as well as cell intrinsic factors such as transcription factors and signal transduction pathway regulators (Christie and Turnley, 2012; Christie et al., 2013a). In general, endogenous adult neural precursor cells can be quite easily induced to proliferate and migrate, and depending on the context, differentiate into neuronal or glial cell types. However, fewer factors have been identified that induce newborn neurons to integrate into the local circuitry and survive more than a few weeks after their birth. Indeed at least 50% of newborn neurons fail to survive longer than a month or two after their generation (Petreanu and Alvarez-Buylla, 2002; Dayer et al., 2003). This makes sense under normal physiological conditions, where newborn neurons replenish local neurons lost due to normal turnover, to homeostatically maintain neuron numbers (Valley et al., 2009). Addition of newborn neurons to existing circuitry has specific functional outcomes. In the olfactory bulb, addition of new neurons is required for short-term olfactory memory, perceptual learning, and for innate olfactory responses (Breton-Provencher et al., 2009; Moreno et al., 2009; Sakamoto et al., 2011). In the hippocampus, adult neurogenesis plays roles in anxiety and affective behaviors, cognition and spatial memory (Ming and Song, 2011), and is proposed to be vital for forgetting of hippocampal-dependent short-term memories (Frankland et al., 2013). However, in instances of larger neuronal loss, such as following injury or disease, this failure of newborn neurons to increase their integration and survival in conjunction with increases in proliferation and redirected migration means that the full potential of adult neural progenitor cells (NPCs) to repair the damage may not be realized. This perspective article will explore some of the mechanisms and factors that may be targeted to enhance newborn neuron survival, summarized in Table 1.

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