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Abstract

Presumably, the 'hard-wired' neuronal circuitry of the adult brain dissuades addition of new neurons, which could potentially disrupt existing circuits. This is borne out by the fact that, in general, new neurons are not produced in the mature brain. However, recent studies have established that the adult brain does maintain discrete regions of neurogenesis from which new neurons migrate and become incorporated into the functional circuitry of the brain. These neurogenic zones appear to be vestiges of the original developmental program that initiates brain formation. The largest of these germinal regions in the adult brain is the subventricular zone (SVZ), which lines the lateral walls of the lateral ventricles. Neural stem cells produce neuroblasts that migrate from the SVZ along a discrete pathway, the rostral migratory stream, into the olfactory bulb where they form mature neurons involved in the sense of smell. The subgranular layer (SGL) of the hippocampal dentate gyrus is another neurogenic region; new SGL neurons migrate only a short distance and differentiate into hippocampal granule cells. Here, we discuss the surprising finding of neural stem cells in the adult brain and the molecular mechanisms that regulate adult neurogenesis.

Chronic Progressive Neurodegeneration in a Transgenic Mouse Model of Prion Disease

“…The generation of new neurons in the sub-granular zone of the dentate gyrus (Lennington et al, 2003) occurs throughout life, and plays an important role in memory functions (Snyder et al, 2005). We therefore examined the rate of neurogenesis in the dentate gyrus of TgMHu2ME199K/KO and wild-type mice at various ages.…”

Subsite Awareness in Neuropathology Evaluation of National Toxicology Program (NTP) Studies

“…In toxicologic pathology, examination of the olfactory bulb is important in inhalation studies. Since the olfactory bulb is a site for neurogenesis (Lennington et al 2003; Whitman and Greer 2009) in adults, the probability of identifying toxicants affecting cell migration and differentiation is increased here. It has been demonstrated that neuroblasts from the subventricular zone migrate along the rostral migratory stream into the olfactory bulb (Jacquet et al 2010), where they differentiate mostly into granule cells.…”

Mechanotransduction: Tuning Stem Cells Fate

“…In addition to the restraints imposed by niche cytoarchitecture, the neural stem cell niche is under the influence of a complex array of diffusible molecules, including growth factors and neurotransmitters [25,26,27,28,29,30,31,32,33]. Many factors appear to influence age-related decreases in neurogenesis, including a reduction in specific growth factors and telomerase levels, changes in cell-cycle modulators, and high levels of corticosteroids and inflammation [34,35,36,37,38,39,40].…”