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　脳を構成するニューロンの大部分は胎生期あるいは生後の初期に神経幹細胞から生まれる。しかし、近年の研究によって成人の脳にも幹細胞が存在し、ニューロンが継続的に産生されていることが明らかになった。成熟した脳におけるニューロンの産生（adult neurogenesis）は、霊長類を含む様々な動物の側脳室の外側壁に存在する脳室下帯

（subventricular zone: SVZ）で観察されている。脳室下帯で生まれるニューロンは長距離を移動し、実際に機能する場所へ到達した後で成熟する。成体脳におけるニューロン新生は脳梗塞、神経変成疾患や外傷など様々な脳のダメージによって変化する。これらの病態によってニューロンが失われると、損傷を受けた領域の周囲に新生ニューロンが出現する。すなわち、ほ乳類の成体脳には、機能回復には不十分であるが、潜在的な再生能力があると考えられる。げっ歯類の中大脳動脈閉塞（MCAO）は脳虚血のモデルとして広く用いられている。傷害後一週間以内に、脳室下帯の神経幹細胞・前駆細胞が増殖し、特殊な形態を示す移動中の幼若ニューロンや新生ニ

ューロンが傷害部位の周囲に観察される。我々はウイルスを用いた細胞特異的な標識方法によって、脳室下帯に存在するGFAP陽性の神経幹細胞によって産生される新生ニューロンが傷害を受けた線条体へ向かって移動し、シナプスを有する成熟ニューロンになることを証明した。この結果は、脳室下帯における継続的なニューロン新生が傷害を受けた脳の神経回路を再生させることに役立つ可能性があることを示唆している。また、脳室下帯は、様々な病態における重要な治療の標的組織であると言える。しかし、脳室下帯由来の新生ニューロンの大部分は線条体に分布し、皮質まで達するものはほとんどない。脳梗塞で脱落するニューロンのうち成熟して神経回路に組み込まれる細胞はわずか0.2％と言われている。また、ニューロン新生は神経回路の再生に関わるだけでなく、様々な脳疾患の病態にも関与している。ニューロン新生の研究を再生医療に応用するためには、正常脳と病態脳の両方におけるニューロン新生の制御機構をより詳細に理解する必要がある。本講演では、我々が動物実験で明らかにした正常時・病態時におけるニューロンの産生・移動・成熟のメカニズムと、それを活かした虚血性脳疾患の再生医療の可能性について述べる。

セッションⅢ脳神経疾患における再生医療講演２

成体脳のニューロン新生：脳に内在する神経再生機構

名古屋市立大学大学院医学研究科再生医学分野教授

略　歴

受賞歴

1996　　東京大学大学院医学系研究科第二基礎医学専攻博士課程修了

1996　　博士（医学）授与1996　　筑波大学基礎医学系助手1997　　大阪大学医学部助手2001　　文部科学省在外研究員（カリフォルニア大学サンフラ

ンシスコ校）2003　　慶應義塾大学医学部講師2005　　慶應義塾大学医学部助教授2007　　名古屋市立大学大学院医学研究科再生医学分野教授2004　　日本神経科学学会奨励賞2006　　日本神経化学会最優秀奨励賞2007　　日本学術振興会賞2007　　科学技術分野の文部科学大臣表彰（若手科学者賞）

澤本 和延

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adult neurogenesis, the alterations seen under pathological conditions, and the likely functional impact of both.

2. Neurogenesis in the hippocampus　　The hippocampus is part of the limbic system, which has important functions in learning and memory and in regulating emotion and mood. Hippocampal neurogenesis takes place in the dentate gyrus (DG) (Fig. 1), which is largely composed of neurons called granule cells that inhabit the granule cell layer (GCL). Granule cells receive input from the entorhinal cortex (perforant path) and subcortical regions, including the raphe nucleus and locus coeruleus. The granule cells project their axons, called mossy fibers, to the CA3 region, where they synapse onto pyramidal cells (Fig. 1A). Neural stem/progenitor cells reside in the SGZ, a thin cell layer between the GCL and the dentate hilus. Although these cells express glial fibrillary acidic protein (GFAP), a marker for mature astrocytes, and have morphological and electrophysiological characteristics of astrocytes, they continuously proliferate and generate new granule cells. Newly-generated granule cells in the SGZ migrate the short distance into the GCL, where they develop dendrites that they extend toward the molecular layer, and axons that they extend into the CA3; they finally differentiate into functional glutamatergic neurons, and are integrated into the neural circuitry of the hippocampus (Fig. 1B, C). About 250,000 cells, equal to about 6 % of the total number of granule cells, are generated every month in the rodent, but only some of them are stably integrated into the neural network. A recent study of adult neural stem cells using a tamoxifen-induced recombination system to activate the expression of a reporter gene permanently in the stem-cell progenies, showed

1. Introduction　　In the mammalian brain, the production of new neurons during adulthood continues in the subventricular zone (SVZ) at the lateral walls of lateral ventricles and in the subgranular zone (SGZ) in the dentate gyrus (DG) of the hippocampus. New neurons generated at these sites migrate toward their final destinations, where they differentiate into mature neurons and are integrated into the neuronal circuitry. Adult neurogenesis is evolutionally conserved in vertebrates, including humans; however, the functional significance of persistent neurogenesis and the mechanisms that maintain it in these specific regions are still not well defined. Recent studies have shown that adult neurogenesis is affected by various pathological conditions (Kaneko and Sawamoto, 2009). While these alterations could contribute to the restoration/regeneration of the damaged nervous system, they sometimes seem to be involved in the pathophysiology of neurological and psychiatric diseases. Here we will overview

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Adult neurogenesis: an endogenous mechanism for brain repair

Professor, Dept. of Developmental and Regenerative Biology, Nagoya City University Graduate School of Medical Sciences

Past Records

Special Awards

Toru Yamashita, Mikiko Ninomiya and Naoko Kaneko Department of Developmental and Regenerative BiologyInstitute of Molecular MedicineNagoya City University Graduate School of Medical Sciences

Completed Ph.D. program, Institute of Medical Science, University of TokyoReceived Ph.D. (Doctor of Medical Science), University of Tokyo Graduate School of Medical ScienceInstructor, Institute of Basic Medical Sciences, University of TsukubaInstructor, Osaka University School of MedicineVisiting Postdoc, University of California San FranciscoAssistant Professor, Keio University School of MedicineAssociate Professor, Keio University School of MedicineProfessor, Dept. of Developmental and Regenerative Biology, Nagoya City University Graduate School of Medical Sciences

Japan Neuroscience Society Young Investigator AwardThe Award for Young Investigator of Japanese Society for NeurochemistryJSPS Prize, Japan Society for the Promotion of ScienceThe Young Scientists’ Prize, Ministry of Education, Culture, Sports, Science and Technology

1996

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19972001200320052007

20042006

20072007

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2A). The SVZ astrocytes are neural stem cells, but they express GFAP and are morphologically indistinguishable from non-neurogenic astrocytes in other regions. The SVZ is thought to provide a specific microenvironment, the “stem cell niche,” for neural stem cells to maintain their self-renewing, multipotent state. Various proteins are reported to be involved in the formation of the niche. For example, basic fibroblast growth factor (FGF2), Notch1, sonic hedgehog (SHH), and ciliary neurotrophic factor (CNTF) play important roles in stem-cell maintenance and/or self-renewal. 　　The stem cel ls prol i ferate slowly and continuously, and they generate transit-amplifying cells (Fig. 2B). In spite of their multipotency in early postnatal life or when cultured under specific conditions, most of the cells generated in the adult SVZ differentiate into olfactory interneurons, at least under physiological conditions. A small number of oligodendrocyte precursors is also produced, which migrate into the corpus callossum. 　　The transit-amplifying cells proliferate quickly, and their progeny then become neuroblasts (Fig. 2B). Unlike stem cells, neuroblasts are committed to the neuronal linage. Recently, we identified the Wnt- β -Catenin signal as a regulator of the proliferation and differentiation of transit-amplifying cells (Adachi et al., 2007). β-Catenin signaling promotes the proliferation of transit-amplifying cells and increases the pool of these cells, which ultimately leads to an increase in the newly-generated neurons of the olfactory bulb (OB). Within a few days of their birth, neuroblasts generated in the SVZ migrate into the OB, the anterior tip of the telencephalon (Fig. 2C). In the rostral migratory stream (RMS), which is the migratory pathway leading to the OB, the migrating neuroblasts typically are bipolar with extended leading and trailing processes, and they form elongated cell aggregates referred to as “chains,” within which the neuroblasts can slide over and past one another. The chains of neuroblasts are surrounded by an astrocytic

that adult neurogenesis makes a relatively minor contribution to the neuronal population of the DG. BrdU-labeling of the newly-generated neurons showed that at least a half of them die within a month, before they can function as mature neurons. Their survival is reported to be regulated by input activities that are mediated by NMDA receptors. GABA, the major inhibitory neurotransmitter in the adult brain, which initially exerts an excitatory action on newly-generated neurons due to their high cytoplasmic chloride content, also regulates the differentiation, maturation and survival of them. However, the precise mechanism for regulating the turnover of granule cells is still unknown.　　Interestingly, in addition to the morphological differences, newly-generated immature neurons show unique electrophysiological activities, distinguishable from those of mature granule cells. In particular, it is easier to induce long-term potentiation in the new neurons than in the mature ones. Their distinct electrophysiological characteristics may indicate that the new neurons play an important role in the hippocampal circuitry, despite their small numbers A number of studies have demonstrated that newly-generated neurons are involved in learning and memory. Several hippocampus-dependent learning tasks increase the proliferation of neuronal progenitors in the SGZ and/or promote the survival of newly-generated neurons, and the animals’ performance of these tasks correlates positively with the amount of neurogenesis. Moreover, the suppression of neurogenesis by irradiation or anti-mitotic drug treatment impairs the animals’ performance. Neurogenesis in the DG dramatically decreases with age, and may contribute to age-related memory deficits.

3. Neurogenesis in the SVZ　　The SVZ is a thin cell layer located in the lateral walls of lateral ventricles (Fig. 2). There are four types of cells in the SVZ: astrocytes, transit-amplifying cells, newly-generated neurons called neuroblasts, and ependymal cells (Fig.

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mutation that causes defective ependymal cilia development and a lack of normal CSF. The CSF flow creates a concentration gradient of diffusible proteins secreted from the choroid plexus in the lateral ventricle. Slit, a chemorepellent that acts as a guidance molecule for migrating cells and extending axons in the developing brain, is one of these proteins. Its concentration gradient is supposed to be present in the ventricle and the adjacent parenchyma, including the SVZ. Because the SVZ neuroblasts react to the chemorepulsive effect of Slit, it is likely that Slit helps guide the rostral migration of SVZ neuroblasts against its concentration gradient. 　　Active cytoskeletal modification also occurs in migrating neuroblasts in the RMS. We found that cyclin-dependent kinase 5, which regulates the cytoskeleton in migrating cells in the embryonic brain, plays a crucial role in the chain formation of neuroblasts in the postnatal SVZ/RMS, and in the speed and direction of their migration (Hirota et al., 2007). Polysialic acid-neural cell adhesion molecule (PSA-NCAM) and β1-integrin expressed on the surface of neuroblasts, matrix metalloproteases produced by neuroblasts, and extracellular matrix molecules including tenascin-C, proteoglycans, and the laminins, have all been shown to be involved in the migration of neuroblasts in the RMS. Although the neuroblasts attach to each other in the elongated clusters, they can still slide past one another within a chain. Thus, the adhesion between neuroblasts must be precisely regulated. Because the chains of neuroblasts are surrounded by glial tubes, the mechanism that controls the neuroblast-astrocyte interaction must also be important for neuroblast migration. A lack of Laminin-integrinβ1 signaling or Neuregulin-ErbB4 signaling has been reported to cause disorganization of the glial tubes in the RMS; however, little is yet known about the interaction between migrating neuroblasts and the surrounding astrocytes. Neuroblasts in the RMS are also guided by several other molecules, including netrin1 (Murase and Horwitz, 2002), prokineticin2, glial cell-line derived neurotrophic

sheath, called a glial tube (Fig. 2C, D). These astrocytes are also reported to behave as stem cells, but their role in the migration of neuroblasts is mostly unknown. Although the RMS begins to appear before birth, the chains of neuroblasts and the glial tubes are distinct features of the adult RMS, and are not observed in the embryo or early postnatal ages. Given these structural differences, the migration of neuroblasts in the adult RMS is apparently controlled by a mechanism distinct from that of the developing brain. 　　Neuroblasts that reach the OB detach from the chain, and the individual cells migrate radially into the granule cell layer (GCL) and the glomerular layer (GL), where they respectively differentiate into two types of olfactory interneurons, the granule cells and periglomerular cells (Fig. 2E). The OB is the first relay station in the olfactory system, where odor information from the olfactory epithelium is transferred to higher centers in the brain. Interneurons are thought to modulate the activity of glutamatergic projection neurons, mitral cells, and tufted cells, and to contribute to odor discrimination. Because the projection neurons are not replaced, newly-generated interneurons are likely to be responsible for the plasticity of the olfactory system. The survival of newly-generated neurons is input-dependent, and about a half of them are eliminated within 6 weeks of their birth. However, how many cells are substantially replaced and how this process is controlled are still matters of controversy.

4. Migration of neuroblasts toward the OB 　　Neuroblasts generated in the SVZ migrate along the RMS at high speed (about 100μm/hour) for a long distance (about 5 mm). Recent studies have revealed a number of molecules to be involved in this specific migratory behavior, and we showed that the rostral migration of neuroblasts is in parallel with the directional flow of cerebrospinal fluid (CSF) in the lateral ventricle (Sawamoto et al., 2006). We found that this directional migration was disrupted by a genetic

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neurons in an adult rat model for transient global ischemia. Furthermore, it has been reported the regeneration of striatal projection neurons lost by middle cerebral artery occlusion (MCAO). A recent study on the human post-mortem brain revealed that cerebral infarction patients produced new neurons following the insult.　　In rodents, MCAO is the most common model for ischemic stroke that causes infarction in the striatum and adjacent parietal cortex. Within a week after the insult, neural stem/progenitor cells in the SVZ begin to proliferate, and neuroblasts with the migratory morphology and newly-generated neurons appear at the boundary of the damaged area in the striatum (Fig. 3C), but the origin of these cells was uncertain. Using viral infection-mediated cell-specific introduction of GFAP expression, we showed that these neurons are generated by GFAP-expressing neural stem cells in the SVZ and migrate radially into the damaged striatum, where they differentiate into mature neurons that form synapses (Yamashita et al., 2006). These observations imply that the continuous production of neurons in the adult SVZ could compensate for the neurons lost to insult, and help regenerate the neuronal circuitry. These findings further imply that the SVZ could be an important therapeutic target in various pathological conditions.　　Immediately after the ischemic lesion, the expression of angiogenesis-related genes, including vascular endothelial growth factor (VEGF), FGF2, and epidermal growth factor (EGF), is markedly increased in the damaged region. These factors are also known to promote the production of new neurons. Angiogenesis in the ischemic region precedes neurogenesis, and vascular endothelial cells release soluble factors that promote the self-renewal of neural stem cells in the SVZ. Notably, recent studies show the vasculature in the SVZ to be an important component of stem cell niches. These observations indicate an important role for vasculature in neuronal regeneration after stroke.　　Neuroblasts migrating in the striatum

factor (GDNF), and brain-derived neurotrophic factor (BDNF), which attract them toward the OB. In the OB, reelin, a secreted glycoprotein, and extracellular matrix tenascin-R are involved in the process of neuroblast detachment from the chain and the beginning of their radial migration. As mentioned above, neuroblasts differentiate into two types of olfactory interneurons in different layers of the OB. Interestingly, a recent study showed that the destination of each neuroblast in the OB, that is, the GCL or GL, is already determined before it leaves the SVZ. Although a subtype of glomerular neuron (tyrosine hydroxylase-expressing cells) is found exclusively in the GL, it is unknown how neuroblasts choose to cease migration in a specific layer, or how some of them migrate past the GCL into the GL. Thus, although previous studies have revealed various molecules that are involved in the migration of neuroblasts in the RMS, the comprehensive mechanism that integrates these signals remains to be elucidated.

5. Alteration of adult neurogenesis after　 ischemic stroke　　Neurogenesis in the adult brain is affected by various brain insults , including stroke, neurodegenerative diseases, and trauma. Following the loss of neurons in these pathological conditions, newly-generated neurons appear in and around the damaged area (Fig. 3A). This finding indicates the potential capacity for regeneration in the mammalian brain, although this spontaneous regeneration is insufficient to induce neurological improvement. After marked neuronal death by ischemic stroke, ectopic neurogenesis can be observed (Fig. 3B). It has been reported that neurogenesis in the DG is markedly increased in an adult gerbil model for transient global ischemia, which causes the death of pyramidal neurons in the CA1 region of the hippocampus; however, the lost CA1 neurons were never replaced in their investigation. In contrast, it has been demonstrated the regeneration of CA1 pyramidal

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are anticipated to be of fundamental importance to studying molecular mechanisms that control SVZ cells and their progeny and for developing novel neuronal self-repair strategies.

6. Conclusion　　Recent studies have identified a variety of molecules that regulate the neurogenesis in the adult brain; however, our understanding of this neurogenesis remains fragmentary. In spite of these limitations, neuroregenerative therapy is strongly anticipated as an effective new strategy for treating neurological and psychiatric diseases that have been resistant to conventional medications or for which there is no current treatment. Although neurogenesis contributes to the regeneration of neuronal circuitry under pathological conditions, it may also be associated with their symptoms and/or pathophysiology. For the development of successful neuroregenerative therapies, it is essential to understand more precisely and comprehensively the mechanisms that regulate neurognesis in both physiological and pathological conditions.

7. AcknowledgmentsWe thank Dr. Hideyuki Okano, Dr. Arturo Alvarez-Buylla, Dr. Kazuhide Adachi, and Dr. Yuki Hirota for their contributions to the original research on adult neurogenesis and members of the Sawamoto Laboratory and the Okano laboratory for their valuable discussion. This work was supported by research grants from the Ministry of Education, Culture, Sports, Science & Technology (MEXT), Ministry of Health, Labor and Welfare (MHLW), Japan Society for the Promotion of Science (JSPS), and Human Frontier Science Program (HFSP).

toward the infarct area frequently form chain-like structures similar to those observed in the RMS. These aligned cells are closely associated with astrocytic processes and blood vessels (Yamashita et al., 2006) (Fig. 3D), and their migration is controlled by stroma cell-derived factor 1 (SDF1) and angiopoietin 1 (Ang1), which are produced by vascular endothelial cells, and by monocyte chemoattractant protein 1 (MCP1), which is expressed by activated microglia and astrocytes in the damaged area. The signals of these molecules are mediated by their respective receptors, CXCR4, Tie2, and CCR2, which are expressed on neuroblasts. 　　Previous reports have described BrdU-labeled newborn cells as expressing markers for mature neurons within the damaged striatum as early as 30 days after the induction of ischemia. We examined the phenotype of SVZ-derived GFP-labeled cells by light and electron microscopy after an extended survival period (Yamashita et al., 2006) (Fig. 4). The labeled cells were found to possess long processes, express NeuN, and form synaptic structures in the damaged striatum 90 days after ischemia induction. These results strongly suggest SVZ cells to have the ability to generate functional mature neurons that survive in the damaged striatum for considerable periods. Based on all of the results of this study, we conclude that SVZ is the main source of the neuroblasts that migrate toward the brain region infarcted by cerebral ischemia, where they differentiate into mature neurons. Our findings indicate that, as an important endogenous cell source, SVZ is a promising therapeutic target for various neurological disorders. However, it remains unclear what types of neurons are generated. In addition, the number of newborn neurons is too small for recovery of neurological functions. Thus, it will be necessary to add appropriate interventions to enhance the proliferation, survival, and/or neuronal maturation of SVZ cells and their progeny. The mechanisms of insult-induced neurogenesis described herein

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References1. Kaneko, N. and Sawamoto, K. (2009) Adult

neurogenes i s and i t s a l t e ra t i on under pathological conditions. Neurosci Res 63, 155-164.

2. Adachi , K. , Mirzadeh, Z. , Sakaguchi , M. , Yamashita, T., Nikolcheva, T., Gotoh, Y., Peltz, G., Gong, L., Kawase, T., Alvarez-Buylla, A., Okano, H., and Sawamoto, K. (2007) b-catenin signaling promotes proliferation of progenitor cells in the adult mouse subventricular zone. Stem Cells 25, 2827-2836.

3. Sawamoto, K., Wichterle, H., Gonzalez-Perez, O., Cholfin, J. A., Yamada, M., Spassky, N., Murcia, N. S., Garcia-Verdugo, J. M., Marin, O., Rubenstein, J. L., Tessier-Lavigne, M., Okano, H., and Alvarez-Buylla, A. (2006) New neurons follow the flow of cerebrospinal fluid in the adult brain. Science 311, 629-632.

4. Hirota, Y., Ohshima, T., Kaneko, N., Ikeda, M., Iwasato, T., Kulkarni, A., Mikoshiba, K., Okano, H., and Sawamoto, K. (2007) Cyclin-dependent kinase 5 is required for control of neuroblast migration in the postnatal subventricular zone. J. Neurosci. 27, 12829-12838.

5. Yamashita, T., Ninomiya, M., Hernandez Acosta, P., Garcia-Verdugo, J. M., Sunabori, T., Sakaguchi, M., Adachi, K., Kojima, T., Hirota, Y., Kawase, T., Araki, N., Abe, K., Okano, H., and Sawamoto, K. (2006) Subventricular zone-derived neuroblasts migrate and differentiate into mature neurons in the post-stroke adult striatum. J Neurosci 26, 6627-6636.

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progenitor cells reside in the SGZ (blue), proliferate, and generate transiently amplifying progenitors that produce immature granule cells (red). These immature cells migrate into the GCL, where they differentiate into mature granule cells (pink) that project to the CA3 (mossy fibers).　　Immunohistochemistry for PSA-NCAM. Immature granule cells having short, thin process reside in the border between the SGZ and the GCL. (Green, PSA-NCAM; blue, Hoechst; scale bar, 10 μm.) DG, dentate gyrus; GCL, granule cell layer; SGZ, subgranular zone; ML, molecular layer.

Figure 1. Neurogenesis in the hippocampus (Kaneko and Sawamoto, Neurosci Res 63, 155-164, 2009.)　　The structure and neuronal circuitry of the DG in the hippocampus of the adult rodent brain. The input to the hippocampus is mainly provided by the entorhinal cortex through the perforant path (gray) to the granule cells (pink) in the molecular layer in the DG. Each granule cell projects an axon (mossy fiber, red line) to the CA3 region, where it synapses onto pyramidal cells (green). 　　Neurogenesis in the DG. Neural stem/

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　　Migration of neuroblasts. Newly-generated neuroblasts in the SVZ migrate toward the OB through the RMS. In the RMS, neuroblasts (red) form chain-like clusters, which are surrounded by an astrocytic sheath (blue), called a glial tube. Immunohistochemistry for doublecortin (Dcx) and glial fibrillary acidic protein (GFAP) in the RMS. The chains of Dcx+ neuroblasts are surrounded by GFAP+ astrocytes. (Scale bar: 50 μm.)　　Neurogenes is in the OB. In the OB, neuroblasts disperse radially from their chain, and differentiate into two kinds of olfactory interneurons, granule cells or periglomerular cells, which reside in the GCL or GL, respectively.　　SVZ, subventricular zone; RMS, rostral migratory stream; GCL, granule cell layer; MCL, mitral cell layer; GL, glomerular layer.

Figure 2. Neurogenesis in the OB (Kaneko and Sawamoto, Neurosci Res 63, 155-164, 2009.)　　Location and structure of the SVZ. The SVZ is located at the lateral wall of the lateral ventricle and consists of four types of cells: ependymal cells (purple), which line the surface of the lateral ventrical and have multiple motile cilia; astrocytes (blue); transit-amplifying cells (light green); and neuroblasts (red). Recent studies suggest the importance of vasculature (pink) in the SVZ stem cell niche.　　　Production of neurons in the SVZ. Astrocytes (blue) in the SVZ are self-renewing neural stem cells that proliferate slowly and produce transit-amplifying cells (light green). Transit-amplifying cells proliferate quickly to produce immature neurons (neuroblasts; red).

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striatum near the infarct area, where they differentiate into mature neurons.　　Mouse brain section 18 days after MCAO, immunostained for Dcx. Many neuroblasts are present in the ipsilateral striatum, but not in the contralateral hemisphere. Some of neuroblasts migrating in the striatum form chain-like clusters (inset, arrowheads). 　　Immunohistochemistry for Dcx (red) and an endothelial cell marker, PECAM1 (green) of a brain section 18 days after MCAO. The chain-like structures of migrating neuroblasts in the striatum are frequently associated with blood vessels.　　MCAO, middle cerebral artery occlusion; SVZ, subventricular zone; OB, olfactory bulb; Dcx, doublecortin.

Figure 3 Neurogenesis in pathological conditions (Kaneko and Sawamoto, Neurosci Res 63, 155-164, 2009.)　　Migration of neuroblasts in physiological and pathological conditions. The migration of neuroblasts generated in the SVZ is restricted to the RMS and OB in physiological conditions (left). In the injured brain, some of the neuroblasts migrate toward the damaged area (right).　　Neurogenesis after MCAO in adult rodents. MCAO causes marked neuronal loss in the ipsilateral striatum and adjacent neocortex (left). About 1 week later, cell proliferation in the ipsilateral SVZ is significantly increased (middle). Two to 3 weeks after MCAO, neuroblasts produced in the SVZ have migrated into the

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(n = 13) in the striatum expressed NeuN, a specific marker for mature neurons. Scale bar = 20 µm.(D) A GFP-positive cell exhibiting neuronal morphology. Scale bar = 20 µm.(E) An electron micrograph showing a GFP-positive axon (asterisk) containing presynaptic vesicles. Scale bar = 0.5 µm.(F) High-power magnification view of the region indicated by the rectangle in E. The postsynaptic density is indicated by arrowheads.

Fig. 4. SVZ-derived neuroblasts differentiate into mature neurons and form synapses in the striatum by 90 days after MCAO (Yamashita et al., J Neurosci 26, 6627-6636, 2006.)(A) Diagram showing the injection site.(B) The pxCANCre plasmid was injected into the lateral ventricle 5 days before MCAO, and the animals were sacrificed 90 days after MCAO.(C) Confocal 3D reconstruction image of a GFP/NeuN double-positive cell. At 90 days after MCAO, 29% of the SVZ-derived GFP-positive cells

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