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Trends in Biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
The cells in the adult brain that have been shown to possess neurogenesis capabilities (the birth of new neurons) are called neural stem cells (NSCs). These NSCs were first reported in adult mice and later they were also found in rats, songbirds, primates, and also in humans. It has been found that adult neurogenesis is mostly restricted in two brain regions, (1) the subventricular zone, which lines the lateral ventricles, and (2) the dentate gyrus of the hippocampal formation. These NSCs can be cultured in vitro as commonly called as neurospheres, floating heterogeneous aggregates of cells that contain a large proportion of stem cells.
Medical biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
The existence of stem cells in the adult brain has been postulated following the discovery that the process of neurogenesis (the birth of new neurons) continues into adulthood in rats. It has since been shown that new neurons are generated in adult mice, songbirds, and primates, including humans. Normally, adult neurogenesis is restricted to two areas of the brain: the subventricular zone, which lines the lateral ventricles, and the dentate gyrus of the hippocampal formation. Although the generation of new neurons in the hippocampus is well established, the presence of true self-renewing stem cells there has been debated. Under certain circumstances, such as following tissue damage due to ischemia, neurogenesis can be induced in other brain regions, including the neocortex. Neural stem cells are commonly cultured in vitro as so-called neurospheres, floating heterogeneous aggregates of cells, containing a large proportion of stem cells. They can be propagated for extended periods of time and differentiated into both neuronal and glia cells and therefore behave like stem cells. However, some recent studies suggest that this behavior is induced by the culture conditions in progenitor cells, the progeny of stem cell division that normally undergoes a strictly limited number of replication cycles in vivo. Furthermore, neurosphere-derived cells do not behave like stem cells when transplanted back into the brain. Neural stem cells share many properties with HSCs. Remarkably, when injected into the blood, neuro-sphere-derived cells differentiate into various cell types of the immune system. Cells that resemble neural stem cells have been found in the bone marrow, the home of HSCs. It has been suggested that new neurons in the dentate gyrus arise from circulating HSCs. Indeed, newborn cells first appear in the dentate, in the heavily vascularized subgranular zone immediately adjacent to blood vessels.
Neurophysiological and molecular approaches to understanding the mechanisms of learning and memory
Published in Journal of the Royal Society of New Zealand, 2021
Shruthi Sateesh, Wickliffe C. Abraham
The two primary brain regions for which adult neurogenesis is well-known are the subventricular zone (SVZ) lining the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus. The SGZ neurogenesis of dentate granule cells has attracted significant attention given its positioning in the hippocampus, suggesting a possible role in the contextual and spatial learning and memory functions of this structure. Indeed, disruption of adult neurogenesis by a variety of means, genetic, pharmacological and x-ray irradiation has been shown to impair water maze learning and contextual fear conditioning, along with complex pattern discrimination (Saxe et al. 2006; Dupret et al. 2008; Clelland et al. 2009; Seo et al. 2015). Neurogenesis also acts to impair retention of recently learned information, a function that may reduce proactive interference of new learning (Akers et al. 2014). The contribution of a particular cohort of adult-born granule cells is particularly prominent during the 4–6 weeks after their genesis, when the granule cells are highly excitable and have a lower threshold for LTP compared to mature granule cells (Ge et al. 2007). However the excitability state of adult-born cell is not fixed upon maturity, as it can be enhanced by enriched environment exposure or LTP induction. This suggests that there may be a prolonged capability for plasticity and contribution to behaviour after their maturity, throughout adulthood (Ohline et al. 2018).