Cellular Organization and Migration Pathways of the Ventricular–Subventricular Zone in the Juvenile Swine Brain (<i>Sus scrofa domesticus</i>)

The ventricular-subventricular zone (V-SVZ), lining the lateral walls of the lateral ventricles, is a major neurogenic region in the adult brain of many mammals. This study investigates the structural organization and cellular composition of the V-SVZ in the juvenile swine brain (3-5 months), providing novel insights into neuroblast migration in gyrencephalic species. Using immunohistochemistry combined with transmission and scanning electron microscopy, we redefined the cytoarchitecture of the swine V-SVZ, identifying four distinct cellular layers. Layer 1 consists of a pseudostratified epithelium of glial fibrillary acidic protein-positive ependymal cells, whose cilia and microvilli extend into the ventricular lumen, frequently surrounding supraependymal axons. Beneath it, layer 2 is composed of astrocytic and radial glia processes and contains occasional clusters of doublecortin (DCX)-positive cells with prominent microtubules and elongated cytoplasm, indicative of a migratory phenotype. Layer 3 is further subdivided into a low-cell-density sublayer 3a, enriched with myelinated axons and scattered DCX⁺ clusters, and a high-cell-density sublayer 3b, characterized by large groups of DCX⁺ migratory cells. In sagittal sections, these cells form long chains oriented parallel to the ventricular surface. Neuroblasts emerging from the dorsal V-SVZ migrate caudorostrally through the rostral migratory stream toward the olfactory bulb. The layered organization of the swine V-SVZ resembles that of humans, where DCX⁺ chains persist up to 18 months of age, positioning the swine as a valuable model for investigating postnatal plasticity and neurogenic potential in gyrencephalic brains. The persistence of immature neurons in the V-SVZ of gyrencephalic mammals, including infant humans, underscores the relevance of this region for neurogenesis and plasticity in large-brained species.