Abstract
Neurogenesis, the formation of new neurons, can be observed in the adult brain of many mammalian species, including humans. Despite significant progress in our understanding of adult neurogenesis, we are still missing data about the extent and location of production of neural precursors in the adult mammalian brain. We used 5-ethynyl-2'-deoxyuridine (EdU) to map the location of proliferating cells throughout the entire adult mouse brain and found that neurogenesis occurs at two locations in the mouse brain. The larger one we define as the main proliferative zone (MPZ), and the smaller one corresponds to the subgranular zone of the hippocampus. The MPZ can be divided into three parts. The caudate migratory stream (CMS) occupies the middle part of the MPZ. The cable of proliferating cells emanating from the most anterior part of the CMS toward the olfactory bulbs forms the rostral migratory stream. The thin layer of proliferating cells extending posteriorly from the CMS forms the midlayer. We have not found any additional aggregations of proliferating cells in the adult mouse brain that could suggest the existence of other major neurogenic zones in the adult mouse brain.
Highlights
Neurogenesis, the formation of new neurons, can be observed in the adult brain of many mammalian species including humans
Previous studies using Bromodeoxyuridine (BrdU), another thymidine analog, showed that mitotic cells labeled with BrdU could be observed in adult mouse brain two hours after BrdU injection, and the two hour time point was proposed as an appropriate time for "a true measure of proliferation" [11]
One hour after EdU injection we did not observe any mitotic cells labeled with EdU showing that one hour is not enough time for the cells to transition from S phase to M phase in the adult brain (Figure 1B)
Summary
Neurogenesis, the formation of new neurons, can be observed in the adult brain of many mammalian species including humans. The new neurons are incorporated into the dentate gyrus and contribute to neuronal plasticity, to the formation of new memories and learning [1,2,3] Another location for neurogenesis is the olfactory bulbs, where new neurons are incorporated to replace worn out olfactory interneurons [4,5,6]. There are reports of new neuron incorporation in other parts of the adult brain Their origin, role, and extent of incorporation is still not fully characterized [6,7,8]. Trauma, and neurodegenerative diseases all lead to the loss of cognitive, motor, and analytical potency in the brain This decline is in part attributed to the loss of neurons. We used EdU to locate proliferating cells involved in neurogenesis in the adult mouse brain
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