Identification of radial glia-like cells in the adult mouse olfactory bulb

Glial cells in the mammalian olfactory bulb

The mammalian olfactory bulb (OB), an essential part of the olfactory system, plays a critical role in odor detection and neural processing. Historically, research has predominantly focused on the neuronal components of the OB, often overlooking the vital contributions of glial cells. Recent advancements, however, underscore the significant roles that glial cells play within this intricate neural structure. This review discus the diverse functions and dynamics of glial cells in the mammalian OB, mainly focused on astrocytes, microglia, oligodendrocytes, olfactory ensheathing cells, and radial glia cells. Each type of glial contributes uniquely to the OB's functionality, influencing everything from synaptic modulation and neuronal survival to immune defense and axonal guidance. The review features their roles in maintaining neural health, their involvement in neurodegenerative diseases, and their potential in therapeutic applications for neuroregeneration. By providing a comprehensive overview of glial cell types, their mechanisms, and interactions within the OB, this article aims to enhance our understanding of the olfactory system's complexity and the pivotal roles glial cells play in both health and disease.

Clonal Mapping of Astrocytes in the Olfactory Bulb and Rostral Migratory Stream

Astrocytes are the most abundant glial population in the central nervous system, where they fulfill multiple essential tasks. Such diverse functions require a heterogeneous population of cells, yet it is still unclear how this cellular heterogeneity emerges during development. To clarify to what extent such diversity is determined by lineage, we have elaborated the first clonal map of astrocytes in the olfactory bulb and rostral migratory stream. Astrocyte clones are comprised of a limited number of cells, which arise from local progenitors and that are arranged following a radial pattern. Although astroglia exhibit a vast morphological diversity, this was layer-dependent rather than determined by lineage. Likewise, lineage did not strictly determine their position, although we found a striking relationship between the clones and olfactory glomeruli. A distinctive morphology and other clonal features, together with the occurrence of immature forms, reflect the singularity of these astroglial populations.

Radial glial cell: critical functions and new perspective as a steroid synthetic cell

The radial glial cell (RGC) is a glial cell type in the central nervous system of all vertebrates. Adult teleost fish have abundant RGCs in the brain in contrast to mammals. Adult fish RGCs have many important functions, including forming a structural scaffold to guide neuronal migration and serving as the progenitor cells in the brain to generate neurons. The role of the RGC in adult neurogenesis explains the high regenerative capacity of adult fish brain. There is increasing evidence from several species that some glial cells produce or metabolize steroids. It is now well-known that teleost RGCs express aromatase and produce estrogens from androgen precursors, which may be important for local neuroendocrine functions and regulation of neurogenesis. The question of whether RGCs are capable of de novo steroid synthesis from cholesterol remains unanswered. However, the expression of steroidogenic acute regulatory protein, and the key enzyme cytochrome P450 17alpha-hydroxylase in primary cultures of goldfish RGCs indicate the potential to produce 17α-hydroxy-pregnenolone and thus other steroid intermediates. The possibility of synthesizing additional non-estrogenic steroids may indicate new functions for the RGC.

The extracellular matrix glycoprotein tenascin-R affects adult but not developmental neurogenesis in the olfactory bulb

Neuronal precursors produced in the subventricular zone throughout an animal's life migrate tangentially along the rostral migratory stream and, once in the olfactory bulb (OB), turn to migrate radially to the bulbar layers, where they differentiate into interneurons. Despite extensive investigations, it has remained largely unknown whether the same molecular mechanisms control OB neurogenesis during early postnatal development and in adulthood. In this study, we show that the extracellular matrix glycoprotein tenascin-R (TNR) is produced in the granule cell layer of the OB and that its expression increases during postnatal development. Time-lapse video imaging and morphological analyses revealed that a lack of TNR decreases the radial migration of neuronal precursors in the adult, but not in the developing OB. A lack of TNR also reduces spine development of newborn neurons in adult mice. To understand the functional consequences of a lack of TNR, we performed electrophysiological and behavioral studies on young and adult mice. Electrophysiological recordings showed that mitral cells, the target cells of newly generated interneurons, receive reduced spontaneous and evoked inhibitory activity in adult, but not young, TNR knock-out mice. Moreover, the synchronized activity of mitral cells was decreased in the OB of adult TNR knock-out mice. Behavioral studies revealed that the lower numbers of newborn interneurons in the adult OB induce alterations in short-term odor memory. Our results indicate that TNR modulates adult but not developmental neurogenesis in the OB and also highlight that the regulation of OB neurogenesis can vary during an animal's lifetime.