Retrospective birth dating of cells in humans
A strong motivation in this research field has been that similar processes are likely to operate in humans, and that alterations in adult neurogenesis could underlie neurological or psychiatric diseases.Moreover, many have hoped that the potential of resident neural stem cells could be harnessed to promote the generation of new neurons for cell replacement in neurological diseases.Several studies have shed light on adult neurogenesis in humans by quantifying the number of cells displaying neuroblast markers in the human postmortem brain. 2011), the neurogenic niche for olfactory bulb neurons in other mammals.In humans, doublecortin (DCX) and polysialylated neuronal cell adhesion molecule (PSA-NCAM)-expressing putative neuroblasts are found in both the dentate gyrus (DG) of the hippocampus (Knoth et al. The density of neuroblasts in both these two regions is highest in the perinatal period, and drops dramatically during the first few postnatal months, to then decline more slowly throughout life (Göritz and Frisén 2012).
A common factor for all strategies used in experimental animals is that they entail first introducing a stable mark in cells, specific for cell proliferation (in the case of labeled nucleotides or retroviruses), or the origin from a candidate stem or progenitor cells (in transgenic strategies), and later assessing whether such a mark is present in mature neurons, which then indicates neurogenesis. In contrast, neurons from all major subdivisions of the human cerebral cortex had C concentrations in genomic DNA that corresponded to the time around the birth of the individual, establishing that most neurons must be as old as the person and that there could have been no major postnatal neurogenesis (Bhardwaj et al. Moreover, analysis of Brd U incorporation in the cerebral cortex in the material procured by Eriksson and Gage (Eriksson et al.
A limitation with the analysis of neuroblast markers is that it is not possible to know whether they differentiate to become mature neurons and integrate long term.
A large number of studies have been performed with markers associated with neurogenesis in several human pathologies (Curtis et al.
There is substantial hippocampal neurogenesis in adult humans, but humans appear unique among mammals in that there is no detectable olfactory bulb neurogenesis but continuous addition of new neurons in the striatum.
There has been an enormous expansion in the knowledge regarding adult neurogenesis in experimental animals over the last two decades.