Abstract
In mammals, new neurons in the adult olfactory bulb originate from a pool of neural stem cells in the subventricular zone of the lateral ventricles. Adult-born cells play an important role in odor information processing by adjusting the neuronal network to changing environmental conditions. Olfactory bulb neurogenesis is supported by several non-neuronal cells. In this review, we focus on the role of astroglial cells in the generation, migration, integration, and survival of new neurons in the adult forebrain. In the subventricular zone, neural stem cells with astrocytic properties display regional and temporal specificity when generating different neuronal subtypes. Non-neurogenic astrocytes contribute to the establishment and maintenance of the neurogenic niche. Neuroblast chains migrate through the rostral migratory stream ensheathed by astrocytic processes. Astrocytes play an important regulatory role in neuroblast migration and also assist in the development of a vasculature scaffold in the migratory stream that is essential for neuroblast migration in the postnatal brain. In the olfactory bulb, astrocytes help to modulate the network through a complex release of cytokines, regulate blood flow, and provide metabolic support, which may promote the integration and survival of new neurons. Astrocytes thus play a pivotal role in various processes of adult olfactory bulb neurogenesis, and it is likely that many other functions of these glial cells will emerge in the near future.
Highlights
The olfactory bulb (OB), which plays a central role in odor information processing, has a multilayered cellular architecture
Transplanting neural stem cells (NSC)/progenitor cells into the subventricular zone (SVZ) of another animal generates OB interneurons, whereas transplanting NSC into non-neurogenic zones limits their neurogenic potential (Alvarez-Buylla and Lim, 2004). These results suggest that the SVZ microenvironment plays an important role in the maintenance of the neurogenic properties of NSC
The downregulation of glycolic metabolism (Gascón et al, 2016) and the forced expression of neurogenic transcriptional factors (Berninger et al, 2007; Heinrich et al, 2010) have been shown to be required for the direct reprogramming of astroglia from cortex into neurons. While it remains to be determined how similar nonneurogenic astrocytes and quiescent NSC are at the level of single cell transcriptomics and what their responses are to different microenvironmental signals, these results suggest that there are similarities in the molecular signatures of these cells
Summary
The olfactory bulb (OB), which plays a central role in odor information processing, has a multilayered cellular architecture. Information processing in the OB is modulated by two other groups of interneurons, that is, periglomerular cells (PG) and granule cells (GC), which form dendro-dendritic synapses with the principal neurons (Urban, 2002; Fukunaga et al, 2014). A substantial number of PGs and GCs are constantly renewed during adulthood. This unusual form of plasticity, which was first brought to light some fifty years ago and was confirmed by subsequent research. Astrocytes play a pivotal role in all these processes. We summarize the current knowledge of the role of astrocytes in adult OB neurogenesis and discuss possible future directions in this exciting field
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