Adult human neurogenesis: early studies clarify recent controversies and go further

Abstract

Evidence on adult mammalian neurogenesis and scarce studies with human brains led to the idea that adult human neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ). However, findings published from 2018 rekindled controversies on adult human SGZ neurogenesis. We systematically reviewed studies published during the first decade of characterization of adult human neurogenesis (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) -when the two-neurogenic-niche concept in humans was consolidated -and compared with further studies. The synthesis of both periods is that adult human neurogenesis occurs in an intensity ranging from practically zero to a level comparable to adult mammalian neurogenesis in general, which is the prevailing conclusion. Nonetheless, Bernier and colleagues showed in 2000 intriguing indications of adult human neurogenesis in a broad area including the limbic system. Likewise, we later showed evidence that limbic and hypothalamic structures surrounding the circumventricular organs form a continuous zone expressing neurogenesis markers encompassing the SGZ and SVZ. The conclusion is that publications from 2018 on adult human neurogenesis did not bring novel findings on location of neurogenic niches. Rather, we expect that the search of neurogenesis beyond the canonical adult mammalian neurogenic niches will confirm our indications that adult human neurogenesis is orchestrated in a broad brain area. We predict that this approach may, for example, clarify that human hippocampal neurogenesis occurs mostly in the CA1subiculum zone and that the previously identified human rostral migratory stream arising from the SVZ is indeed the column of the fornix expressing neurogenesis markers.

Neurogenesis in neurodegenerative diseases in the adult human brain

“…The publication caused quite a stir in the scientific community and aroused a lot of emotions. It also stands in opposition to numerous publications which confirm the formation of new neurons in SVZ and DG in animal models also in neurodegenerative diseases in human [ 5 ]. There are still many unresolved questions about neurogenesis.…”

Memantine in the Prevention of Radiation-Induced Brain Damage: A Narrative Review

“…More precisely, the question could be: “Is there a link between early CD and severe patients’ loss in the early follow-up period?” A possible explanation seems to be provided by further recent neurophysiological evidence. In fact, according to the latter, the subgranular zone of the hippocampus and the subventricular zone of the lateral ventricles are not the only niches providing neural progenitors [ 189 ]. The first demonstrations of a large periventricular area expressing neurogenesis markers, also in adults, date back to 2000.…”

Neurogenesis as a Tool for Spinal Cord Injury

“…The subgranular zone of the gyrus dentate is involved in learning and memory (reviewed in [ 15 ]). Thereafter, the striatum, along with other areas, were reported as an additional neurogenic niche in humans [ 16 , 17 ]. While the differentiation potential of neural stem cells in the brain neurogenic regions has been known for decades, there are ongoing debates regarding the multipotent differentiation potential of the ependymal cells of the central canal in the spinal cord (SCECs).…”