Neuronal migration is a crucial process not only for brain development but also for neural regeneration after injury. It has been reported that some new neurons generated in the ventricular-subventricular zone (V-SVZ) migrate toward tissue injured by ischemic stroke and other forms of brain damage. These migrating neurons can partially compensate for lost neurons and contribute to functional recovery, including improvements in motor function. Therefore, understanding the mechanisms that regulate neuronal migration is expected to facilitate the development of novel therapeutic strategies that enhance endogenous neural regeneration after brain injury.In this review, we discuss the migratory mechanisms of new neurons generated in the V-SVZ and summarize current insights into strategies aimed at promoting neuronal migration and neuronal replacement in the injured brain.

OBJECTIVES:2-Ethyl-1-hexanol (2EH) is a volatile organic compound that can cause sick building syndrome and can be released from flooring materials for more than 10 years through the hydrolysis of compounds with 2-ethylhexyl moieties. Previous studies using mice have raised concerns about tissue-damaging effects on the olfactory epithelium (OE), olfactory bulb (OB), brain, lungs, and skin. A subchronic mouse study observed degeneration of OE at concentrations as low as 20 ppm. However, the effects of long-term exposure to 2EH remain unclear. This study aimed to elucidate the histopathological effects of chronic exposure to 2EH relative to its airborne concentration. METHODS:Ten-week-old male ICR mice were exposed to 0, 0.5, 10, or 100 ppm 2EH by inhalation for 8 h/d, 5 d/wk, for 6 months. Subsequently, histopathological analysis was conducted. RESULTS:At 0.5 ppm, acute and chronic inflammation were observed in the OE and alveoli, with tissue repair in the OE, and thickening of the epithelium and smooth muscle in the bronchi. Metaplasia of OE in the respiratory epithelium was induced at 10 and 100 ppm. At all concentrations, the number of mature neurons in the OE and immature neurons in the OB decreased, suggesting that olfactory nerve activity was suppressed. Fibroblasts increased in the dorsal skin. Microglia in the hippocampus and amygdala increased in number. CONCLUSIONS:Chronic inhalation exposure at airborne concentrations of 2EH as low as 0.5 ppm caused inflammation in the OE, OB, segmental bronchi, and alveoli, and affected the target area of OB neurons.

In this study, we aim to theoretically investigate antipolar cell-cell adhesion, in which adhesion sites are located on the opposite side of the leading edge of migrating cells, as a candidate for irregularly polarized adhesion that induces disorder in collective cell migration. We employ the cellular Potts model to simulate the effects of antipolar adhesion on collective migration driven by cell motility. Antipolar adhesion induces a collective motility disorder, which exhibits a disordered configuration in the motility direction, even when collective motion occurs in the absence of adhesion. Consequently, antipolar adhesion inhibits collective migration. The effect is in contrast to that of polar adhesion, which accelerates the directional intercellular order of cell motility. At a specific motility strength, a depinning transition emerges from a collective motility disorder to a collective motion. The collective motility disorder can be physically explained by the cooperative effect between antipolar adhesion and motility persistence within the mean-field approximation.

Oligodendrocyte progenitor cells (OPCs) generated in the ventricular-subventricular zone (V-SVZ) migrate long distances to sites of brain injury to contribute to remyelination, but the mechanisms guiding their efficient recruitment remain unclear. Using a neonatal cortical injury model combined with live imaging and three-dimensional culture, we show that V-SVZ-derived OPCs migrate toward lesions by interacting with migrating neuroblasts that share the same route. Neuroblast contact significantly enhances OPC motility even in the absence of external scaffolds. High-resolution imaging reveals that these heterotypic interactions are associated with punctate adherens junctions that form and dissolve dynamically during migration. These findings uncover a previously unrecognized mechanism in which transient, dynamic adherens junctions support cooperative migration between neuronal and glial progenitors to facilitate efficient recruitment of OPCs to injured brain tissue.

The ventricular-subventricular zone (V-SVZ) is the largest neurogenic niche in the postnatal mammalian brain, but its organization and migratory dynamics remain poorly understood in gyrencephalic species. Here, we provide ultrastructural and three-dimensional characterization of the V-SVZ neuroblasts in postnatal microminipigs, the smallest pig strain with unique advantages for experimental neuroscience. Transmission electron microscopy revealed developmental changes in cell composition and cytoarchitecture, with migratory neuroblasts consistently associated with glial cells and vasculatures. Notably, serial block-face scanning electron microscopy revealed that tier 3 neuroblasts, a gyrencephalic-specific population, formed elongated, chain-like clusters aligned along vessels, with conserved intracellular features such as polarized organelle distributions and growth cone extension. Radial glial fibers were prominent in neonates but diminished with age, suggesting a developmental shift to vascular scaffolds as primary migration guides. These findings establish microminipigs as a tractable gyrencephalic model for studying postnatal neurogenesis, offering new opportunities for translational research on brain repair.

The developing gyrencephalic brain contains a large population of neural stem cells in the ventricular zone and outer subventricular zone (OSVZ), the latter populated by outer radial glia (oRG). The role of oRG during postnatal development is not well understood. We show that oRG cells increase proliferative capacity and contribute to oligodendrocyte precursor cell (OPC) production following brain injury in human infants and neonatal piglets, whose brains resemble the human brain in structure and development. RNA sequencing revealed oRG-specific transcriptional responses to injury in piglets and showed that the activating transcription factor 5 (ATF5) pathway positively regulates oRG proliferation. Intranasal activation of ATF5 using salubrinal enhanced OSVZ-derived oligodendrogenesis in the injured periventricular white matter and improved functional recovery. These results reveal a key role for postnatal oRG in brain injury recovery and identify ATF5 as a potential therapeutic target for treating white matter injury in infants.

Birth is one of the most important life events for animals. However, its significance in the developmental process is not fully understood. Here, we found that birth-induced alteration of glutamine metabolism in radial glia (RG), the embryonic neural stem cells (NSCs), is required for the acquisition of quiescence and long-term maintenance of postnatal NSCs. Preterm birth impairs this cellular process, leading to transient hyperactivation of RG. Consequently, in the postnatal brain, the NSC pool is depleted and neurogenesis is decreased. We also found that the maintenance of quiescent RG after preterm birth improves postnatal neurogenesis. This study demonstrates the significance of birth in the maintenance of quiescent NSCs.

A common feature of various postnatal stem cells is their close association with blood vessels. Postnatal neural stem cells (NSCs) in the ventricular-subventricular zone originate from fetal radial glia (RG), which possess NSC properties. Here, using live imaging and three-dimensional (3D) electron microscopy, we investigated how RG convert into postnatal NSCs and characterized the fine 3D morphology of the ventricular-subventricular zone. We found that preterm birth disrupts RG-endothelial cell interactions during this transformation, impairing both the structure and stemness of adult NSCs. These findings underscore the importance of a birth-dependent transformation. Our results indicate that RG fiber transection, which depends on the birth process, and endfoot formation on blood vessels, which depends on birth timing, are both critical steps in the conversion of RG into adult NSCs.

Neuronal migration continues to be a key endogenous mechanism in the brain beyond the developmental and newborn stages; however, it remains underutilized in current strategies for neural repair. In mammals, including humans, new neurons are generated from neural stem/progenitor cells located in specific brain regions and migrate toward particular targets. Following brain injury, these cells are recruited to lesion sites; however, without therapeutic intervention, the process is typically limited, with few cells ultimately reaching the target. Recent advances in biomaterials research have introduced scaffold-based strategies to redirect and enhance this migratory capacity. These approaches aim not only to mimic native migratory pathways, such as blood vessels and glial fibers, but also to function as bioactive platforms capable of modifying their local microenvironment. In this perspective, we examine how scaffold-based systems support and guide neuronal migration in brain repair, evaluate representative materials, and highlight challenges for clinical translation.

The growth cone is a highly motile tip structure that guides axonal elongation and directionality in differentiating neurons. Migrating immature neurons also exhibit a growth cone-like structure (GCLS) at the tip of the leading process. However, it remains unknown whether the GCLS in migrating immature neurons shares the morphological and molecular features of axonal growth cones and can thus be considered equivalent to them. Here, we describe a detailed method for time-lapse imaging and optical manipulation of growth cones using a super-resolution laser-scanning microscope. To observe growth cones in elongating axons and migrating neurons, embryonic cortical neurons and neonatal ventricular-subventricular zone (V-SVZ)-derived neurons, respectively, were transfected with plasmids encoding fluorescent protein-conjugated cytoskeletal probes and three-dimensionally cultured in Matrigel, which mimics the in vivo background. At 2-5 days in vitro, the morphology and dynamics of these growth cones and their associated cytoskeletal molecules were assessed by time-lapse super-resolution imaging. The use of photoswitchable cytoskeletal inhibitors, which can be reversibly and precisely controlled by laser illumination at two different wavelengths, revealed the spatiotemporal regulatory machinery and functional significance of growth cones in neuronal migration. Furthermore, machine learning-based methods enabled us to automatically segment growth cone morphology from elongating axons and the leading process. This protocol provides a cutting-edge methodology for studying the growth cone in developmental and regenerative neuroscience, being adaptable for various cell biology and imaging applications. Key features • Three-dimensional primary culture of migrating and differentiating neurons in Matrigel. • Visualization of fine morphology and dynamics of growth cones using super-resolution imaging. • Optical manipulation of cytoskeletal molecules in growth cones using photoswitchable inhibitors. • Machine learning-based extraction of growth cone morphology.

Neonatal brain injury, typically caused by hypoxia-ischemia (HI), results in irreversible cortical and white matter damage, leading to severe neurological sequelae. Therapeutic hypothermia, the only available clinical intervention, has limited effectiveness and is not suitable for all patients. Molecular hydrogen gas exerts neuroprotective effects due to its antioxidant properties and is gaining attention as a potential therapeutic strategy. However, its cellular and molecular effects in the injured neonatal brain are poorly understood. Using a robust HI brain injury model in neonatal piglets, whose brain structure and development closely resemble those of human neonates, we investigated the cell type-specific impact of hydrogen gas following neonatal HI injury and examined the potential molecular mediators underlying its neuroprotective effects. Hydrogen gas treatment significantly attenuated HI-induced apoptosis in both cortical neurons and white matter oligodendrocytes, thereby preserving their cell densities to levels comparable to uninjured controls. These neuroprotective effects were accompanied by reduced microglial activation, astrocyte expansion and myelin loss. RNAscope analyses revealed that hydrogen gas upregulated the expression of the anti-apoptotic factor activating transcription factor 5 (ATF5) in both neurons and mature oligodendrocytes, suggesting a cell-specific protective mechanism. These findings demonstrate that hydrogen gas exerts robust neuroprotection for cortical neurons and white matter oligodendrocytes following neonatal HI injury, and ATF5 is a potential mediator of its anti-apoptotic effects. Our study highlights the clinical feasibility of hydrogen gas as a novel therapeutic strategy for neonatal brain injury.

Migrating neurons form a growth cone at the tip of their leading process. This specialized structure shares striking anatomical and functional similarities with axonal growth cones. We hypothesize that both cones respond to common extracellular cues and direct neuronal migration and axon extension, respectively, through analogous mechanisms. Guidance cues provide growth cones with attractive or repulsive signals to direct them towards their targets. By binding to specific receptors on growth cones, these cues trigger intracellular signaling pathways that reorganize the cytoskeleton and propel neurons or axons in precise directions. Notably, many of the receptors that mediate axon guidance are also present in the growth cones of migrating neurons, reinforcing the idea of a conserved molecular machinery. Elucidating the molecular mechanisms underlying growth cone dynamics in migrating neurons promises to deepen our understanding of neuronal development, and to pave the way for new regenerative therapies aimed at promoting neuronal migration.

In animal tissues, several cell types migrate along blood vessels, raising the possibility that blood flow influences cell migration. Here, we show that blood flow promotes the migration of new olfactory-bulb neurons in the adult mammalian brain. Neuronal migration is facilitated by blood flow, leading to accumulation of new neurons near blood vessels with abundant blood flow. Blood flow inhibition attenuates blood vessel-guided neuronal migration, suggesting that blood contains factors beneficial to neuronal migration. We found that ghrelin, which is increased in blood by hunger, directly influences neuronal migration. Ghrelin signaling promotes somal translocation by activating actin cytoskeleton contraction at the rear of the cell soma. New neurons mature in the olfactory bulb and contribute to the olfactory function for sensing odorants from food. Finally, we show that neuronal migration is increased by calorie restriction, and that ghrelin signaling is involved in the process. This study suggests that blood flow promotes neuronal migration through blood-derived ghrelin signaling in the adult brain, which could be one of the mechanisms that improves the olfactory function for food-seeking behavior during starvation.

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.

In the ventricular-subventricular-zone (V-SVZ) of the postnatal mammalian brain, immature neurons (neuroblasts) are generated from neural stem cells throughout their lifetime. These V-SVZ-derived neuroblasts normally migrate to the olfactory bulb through the rostral migratory stream, differentiate into interneurons, and are integrated into the preexisting olfactory circuit. When the brain is injured, some neuroblasts initiate migration toward the lesion and attempt to repair the damaged neuronal circuitry, but their low regeneration efficiency prevents functional recovery. Elucidation of the molecular basis of neuroblast migration toward lesions is expected to lead to the development of new therapeutic strategies for brain regenerative medicine. Here, we show gene expression profiles of neuroblasts migrating in the peri-injured cortex compared with those migrating in the V-SVZ using photo-isolation chemistry, a method for spatial transcriptome analysis. Differentially expressed gene analysis showed that the expression levels of 215 genes (97 upregulated and 118 downregulated genes) were significantly different in neuroblasts migrating in the peri-injured cortex from those migrating in the V-SVZ. Gene Ontology analysis revealed that in neuroblasts migrating in the peri-injured cortex, expression of genes involved in regulating migration direction and preventing cell death was upregulated, while the expression of genes involved in cell proliferation and maintenance of the immature state was downregulated. Indeed, neuroblasts migrating in the peri-injured cortex had significantly lower Cyclin D2 mRNA and Ki67 protein expression levels than those in the V-SVZ. In the injured brain, amoeboid microglia/macrophages expressed transforming growth factor-β (TGF-β), and neuroblasts migrating in the peri-injured cortex expressed TGF-β receptors. Experiments using primary cultured neuroblasts showed that application of TGF-β significantly decreased proliferating cells labeled with BrdU. These data suggest that the proliferative activity of neuroblasts migrating toward lesions is suppressed by TGF-β secreted from cells surrounding the lesion. This is the first comprehensive study characterizing the gene expression profiles of neuroblasts migrating in the peri-injured cortex.

Axonal growth cones mediate axonal guidance and growth regulation. We show that migrating neurons in mice possess a growth cone at the tip of their leading process, similar to that of axons, in terms of the cytoskeletal dynamics and functional responsivity through protein tyrosine phosphatase receptor type sigma (PTPσ). Migrating-neuron growth cones respond to chondroitin sulfate (CS) through PTPσ and collapse, which leads to inhibition of neuronal migration. In the presence of CS, the growth cones can revert to their extended morphology when their leading filopodia interact with heparan sulfate (HS), thus re-enabling neuronal migration. Implantation of an HS-containing biomaterial in the CS-rich injured cortex promotes the extension of the growth cone and improve the migration and regeneration of neurons, thereby enabling functional recovery. Thus, the growth cone of migrating neurons is responsive to extracellular environments and acts as a primary regulator of neuronal migration.

In the injured brain, new neurons produced from endogenous neural stem cells form chains and migrate to injured areas and contribute to the regeneration of lost neurons. However, this endogenous regenerative capacity of the brain has not yet been leveraged for the treatment of brain injury. Here, we show that in healthy brain chains of migrating new neurons maintain unexpectedly large non-adherent areas between neighboring cells, allowing for efficient migration. In instances of brain injury, neuraminidase reduces polysialic acid levels, which negatively regulates adhesion, leading to increased cell-cell adhesion and reduced migration efficiency. The administration of zanamivir, a neuraminidase inhibitor used for influenza treatment, promotes neuronal migration toward damaged regions, fosters neuronal regeneration, and facilitates functional recovery. Together, these findings shed light on a new mechanism governing efficient neuronal migration in the adult brain under physiological conditions, pinpoint the disruption of this mechanism during brain injury, and propose a promising therapeutic avenue for brain injury through drug repositioning.

Activation of astrocytes after sensory stimulation has been reported to be involved in increased blood flow in the central nervous system. In the present study, using a chemogenetic method to induce astrocyte activation in mice without sensory stimulation, we found that astrocytic activation led to increased blood flow in the olfactory bulb, suggesting that astrocyte activation is sufficient for increasing blood flow in the olfactory bulb. The technique established here will be useful for studying the mechanisms underlying sensory input-dependent blood flow increases.