Résumé
The subventricular zone (SVZ) is a region situated on the outside wall of each lateral ventricle of the vertebrate brain. It is present in both the embryonic and adult brain. In embryonic life, the SVZ refers to a secondary proliferative zone containing neural progenitor cells, which divide to produce neurons in the process of neurogenesis. The primary neural stem cells of the brain and spinal cord, termed radial glial cells, instead reside in the ventricular zone (VZ) (so-called because the VZ lines the inside of the developing ventricles). In the developing cerebral cortex, which resides in the dorsal telencephalon, the SVZ and VZ are transient tissues that do not exist in the adult. However, the SVZ of the ventral telencephalon persists throughout life. The adult SVZ is composed of four distinct layers of variable thickness and cell density as well as cellular composition. Along with the dentate gyrus of the hippocampus, the SVZ is one of two places where neurogenesis has been found to occur in the adult mammalian brain. Adult SVZ neurogenesis takes the form of neuroblast precursors of interneurons that migrate to the olfactory bulb through the rostral migratory stream. The SVZ also appears to be involved in the generation of astrocytes following a brain injury. The innermost layer (Layer I) contains a single layer (monolayer) of ependymal cells lining the ventricular cavity; these cells possess apical cilia and several basal expansions that may stand in either parallel or perpendicular to the ventricular surface. These expansions may interact intimately with the astrocytic processes that are interconnected with the hypocellular layer (Layer II). The secondary layer (Layer II) provides for a hypocellular gap abutting the former and has been shown to contain a network of functionally correlated Glial Fibrillary Acid Protein (GFAP)-positive astrocytic processes that are linked to junctional complexes, yet lack cell bodies except for the rare neuronal somata.
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