Assessment of Neurogenesis and White Matter Regeneration

Persistent neurogenesis occurs in discrete regions of the brain through neonatal to adult period, including the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG) (J Comp Neurol 124:319–335, 1969) and the subventricular zone of the lateral ventricle (J Comp Neurol 137:433–458, 1969). After Eriksson et al. showed that the human hippocampus retains an ability to generate neurons throughout life (Nat Med 4:1313–1317, 1998), it is now expected that neurogenesis has a potential to compensate for and recover neural functions that were destroyed by central nervous system disorders. In fact, since Liu et al. (J Neurosci 18:7768–7778, 1998) first showed that ischemia stimulates neurogenesis in the SGZ of the DG using gerbil forebrain transient ischemia model, the ability of neurogenesis and neuronal repair in the ischemic brain has been reported not only in adult ischemia models (Nat Med 8:963–970, 2002; Ann Neurol 52:802–813, 2002; Cell 110:429–441, 2002; J Clin Invest 114:330–338, 2004), but also in neonatal hypoxia–ischemia (NHI) models (Neurobiol Dis 16:585–595, 2004; Brain Res 1038:41–49, 2005; Neurol Res 28:461–468, 2006). Neurogenesis can be divided into three stages: (1) neural stem/progenitor cells proliferation, (2) neural stem/progenitor cells migration, and (3) differentiation to mature neurons, astrocytes, and oligodendrocytes (OLs) (Science 287:1433–1438, 2000). In ischemic brain, the period of increasing neural stem/progenitor cells’ proliferation and migration is very limited, so it is very important to choose the adequate period to investigate the stimulation of neurogenesis under postischemic condition (Neurol Res 28:461–468, 2006; Brain Res 902:288–293, 2001; J Cereb Blood Flow Metab 22:411–419, 2002; J Cereb Blood Flow Metab 23:331–341, 2003). OLs’ proliferation (oligodendrogenesis) is quite different from neuronal and glial cell proliferation because early oligodendrocyte progenitor cells (OPCs), which can proliferate under normal and pathogenic conditions, exist not only in white matter, but also in gray matter (J Neurosci Res 69:826–836, 2002). In the developing brain, OLs can be divided into four stages during its maturation: (1) early OPCs, (2) late OPCs, (3) immature OLs, and (4) mature OLs (Trends Cell Biol 3:191–197, 1993; J Neurosci 22:455–463, 2002). A lot of late OPCs in the developing brain, including neonatal brain, are very vulnerable to hypoxia or ischemia (J Neurosci 22:455–463, 2002). Therefore, the investigation of how early OPCs increase and reproduce myelin sheath after lack of late OPCs post NHI (Stroke 41:1032–1037, 2010) becomes significant. This chapter introduces a brief history of assessment of neurogenesis and white matter regeneration in models of NHI, as well as the required materials and tools for performing the assessment using methods, such as immunohistochemistry and immunofluorescence.