One striking feature of dentate gyrus development, distinct from the other cortical structures, is the relocation of neural precursors from the ventricular zone to the forming dentate pole to produce a lifelong neurogenic subgranular zone (SGZ). In this study, we demonstrate that dentate progenitors first dwell for up to 1 week in a previously unrecognized neurogenic zone intimately associated with the pial meningeal surface lining the outer edge of the forming dentate. This zone also serves as the organizational matrix for the initial formation of the dentate glial scaffolding. Timely clearance of neural precursors from their transient location depends on reelin, whereas initial formation of this transient stem cell niche requires Cxcl12-Cxcr4 signaling. The final settlement of the neural precursors at the subgranular zone relies on a pertussis toxin-sensitive pathway independent of Cxcl12-Cxcr4 signaling. Furthermore, genetic fate-mapping analysis suggests that subpial precursors contribute to the SGZ formation. These results demonstrate that the relocation of neural precursors in the dentate gyrus consists of discrete steps regulated by multiple pathways.
"First, the granule cells of the outer shell (Figure 1, blue) originate prenatally from the neuroepithelium (NE) located near the fimbria and migrate from the progressively receding secondary dentate matrix to the subpial zone (SPZ; Figure 1, blue). The first dentate migration (dgml) is the source of the earliest generated granule cells that will constitute the outer shell of the granular layer (Altman and Bayer, 1990a,b; Li et al., 2009). During the second postnatal phase (Figure 1, red), the precursor cells build up a new proliferation zone distributed within the hilus, and the early embryonic radial glial scaffold from the ventricular zone (VZ) is replaced by a secondary glial scaffold that traverses the hilus (Figure 1, green). "
[Show abstract][Hide abstract] ABSTRACT: Adverse early life experience decreases adult hippocampal neurogenesis and results in increased vulnerability to neuropsychiatric disorders. Despite that the effects of postnatal stress on neurogenesis have been widely studied in adult individuals, few efforts have been done to evaluate its immediate effects on the developing hippocampus. Moreover, it is not clear whether postnatal stress causes a differential impact in hippocampus development in male and female neonates that could be related to emotional deficits in adulthood. It has been proposed that the long term effects of early stress exposure rise from a persistent HPA axis activation during sensitive time windows; nevertheless the exact mechanisms and mediators remain unknown. Here, we summarize the immediate and late effects of early life stress on hippocampal neurogenesis in male and female rat pups, compare its later consequences in emotionality, and highlight some relevant mediator peptides that could be potentially involved in programming.
"We previously observed small number of cells expressing Prox1 weakly in E14.5 at around the dentate notch (Sugiyama et al., 2013). However, there are discrepancies in the onset of Prox1 expression, and some papers have reported earlier Prox1 expression in the medial telencephalon than our previous observation (Bagri et al., 2002; Galceran et al., 2000; Galichet et al., 2008; Hodge et al., 2012, 2013; Lavado et al., 2010; Li et al., 2009; Liu et al., 2000; Oliver et al., 1993; Seki et al., 2013; Sugiyama et al., 2013; Zhou et al., 2004). We improved our protocol to enhance sensitivity, and could detect Prox1 immunoreactivity at E11.5 (data not shown) and at E12.5 (Fig. 2C), but not at E10.5 (data not shown) in the medial telencephalon. "
"During this time, newborn neurons populate the same anatomical space as cells born during adulthood, but at a considerably (up to 300%) higher rate (He and Crews, 2007). Finally in adulthood, which begins at approximately postnatal day 56 (P56), neurogenesis continues in the SGZ, but at a lower and continuously declining rate throughout life (Zhao et al., 2008; Li et al., 2009). In adolescent and adult mice SGZ neural precursors differentiate into new neurons and functionally integrate into the granule cell layer (Toni et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: Recent evidence implicates adult hippocampal neurogenesis in regulating behavioral and physiologic responses to stress. Hippocampal neurogenesis occurs across the lifespan, however the rate of cell birth is up to 300% higher in adolescent mice compared to adults. Adolescence is a sensitive period in development where emotional circuitry and stress reactivity undergo plasticity establishing life-long set points. Therefore neurogenesis occurring during adolescence may be particularly important for emotional behavior. However, little is known about the function of hippocampal neurons born during adolescence. In order to assess the contribution of neurons born in adolescence to the adult stress response and depression-related behavior, we transiently reduced cell proliferation either during adolescence, or during adulthood in GFAP-Tk mice. We found that the intervention in adolescence did not change adult baseline behavioral response in the forced swim test, sucrose preference test or social affiliation test, and did not change adult corticosterone responses to an acute stressor. However following chronic social defeat, adult mice with reduced adolescent neurogenesis showed a resilient phenotype. A similar transient reduction in adult neurogenesis did not affect depression-like behaviors or stress induced corticosterone. Our study demonstrates that hippocampal neurons born during adolescence, but not in adulthood are important to confer susceptibility to chronic social defeat.
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