The cellular composition and morphological organization of the rostral migratory stream in the adult human brain

The rostral migratory stream (RMS) is the major pathway by which progenitor cells migrate from the subventricular zone (SVZ) to the olfactory bulb (OB) in rodents, rabbits and primates. However, the existence of an RMS within the adult human brain has been elusive. Immunohistochemical studies utilising cell-type specific markers for early progenitor cells (CD133), proliferating cells (PCNA), astrocytes and type B cells (GFAP) and migrating neuroblasts (PSA-NCAM), reveal that the adult human RMS is organized into layers containing glial cells, proliferating cells and neuroblasts. In addition, the RMS is arranged around a remnant of the ventricular cavity that extends from the SVZ to the OB as seen by immunohistological staining analysis and electron microscopy, showing the presence of basal bodies and a typical 9 + 2 arrangement of tubulin in tufts of cilia from all levels of the RMS. Overall, these findings suggest that a pathway of migratory progenitor cells similar to that seen in other mammals is present within the adult human brain and that this pathway could provide for neurogenesis in the human forebrain. These findings contribute to the scientific understanding of adult neurogenesis and establish the detailed cytoarchitecture of this novel neurogenic niche in the human brain.     

Chemoattractive activity of sonic hedgehog in the adult subventricular zone modulates the number of neural precursors reaching the olfactory bulb

The adult subventricular zone (SVZ) supports neural stem cell self-renewal and differentiation and continually gives rise to new neurons throughout adult life. The mechanisms orienting the migration of neuroblasts from the SVZ to the olfactory bulb (OB) via the rostral migratory stream (RMS) have been extensively studied, but factors controlling neuroblast exit from the SVZ remain poorly explored. The morphogen Sonic Hedgehog (Shh) displays proliferative and survival activities toward neural stem cells and is an axonal chemoattractant implicated in guidance of commissural axons during development. We identify here the presence of Shh protein in SVZ extracts and in the cerebrospinal fluid of adult mice, and we demonstrate that migrating neuroblasts in the SVZ and RMS express the Shh receptor Patched. We show that Shh displays a chemoattractive activity in vitro on SVZ-derived neuronal progenitors, an effect blocked by Cur61414, a Smoothened antagonist. Interestingly, Shh-expressing cells grafted above the RMS of adult mice exert a chemoattractive activity on migrating neuroblasts in vivo, thus inducing their accumulation and deviation from their normal migratory pathway. Furthermore, the adenoviral transfer of Shh into the lateral ventricle or the blocking of Shh present in the SVZ of adult mice using its physiological antagonist Hedgehog interacting protein or neutralizing Shh antibodies provides in vivo evidence that Shh can retain SVZ-derived neuroblasts. The ability to modulate the number of neuroblasts leaving the SVZ and reaching the OB through the chemoattractive activity of Shh suggests a novel degree of plasticity in cell migration of this adult stem cell niche.     

Age-dependent regional changes in the rostral migratory stream

Throughout life the subventricular zone (SVZ) is a source of new olfactory bulb (OB) interneurons. From the SVZ, neuroblasts migrate tangentially through the rostral migratory stream (RMS), a restricted route approximately 5 mm long in mice, reaching the OB within 10–14 days. Within the OB, neuroblasts migrate radially to the granule and glomerular layers where they differentiate into granule and periglomerular (PG) cells and integrate into existing synaptic circuits. SVZ neurogenesis decreases with age, and might be a factor in age-related olfactory deficits. However, the effect of aging on the RMS and on the differentiation of interneuron subpopulations remains poorly understood. Here, we examine RMS cytoarchitecture, neuroblast proliferation and clearance from the RMS, and PG cell subpopulations at 6, 12, 18, and 23 months of age. We find that aging affects the area occupied by newly generated cells within the RMS and regional proliferation, and the clearance of neuroblasts from the RMS and PG cell subpopulations and distribution remain stable.     

Expression of amyloid precursor protein-like molecule in astroglial cells of the subventricular zone and rostral migratory stream of the adult rat forebrain

In adult mammals, new neurons in the subventricular zone (SVZ) of the lateral ventricle (LV) migrate tangentially through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they mature into local interneurons. Using a monoclonal antibody for the beta-amyloid precursor protein (APP) (mAb 22C11), which is specific for the amino-terminal region of the secreted form of APP and recognizes all APP isoforms and APP-related proteins, immunoreactivity was detected in specific subpopulations of cells in the SVZ and RMS of the adult rat forebrain. In the SVZ, APP-like immunoreactivity was detected in the ependymal cells lining the LV and some of the subependymal cells. The latter were regarded as astrocytes, because they were positive for the glial markers, S-100 protein (S-100) and glial fibrillary acidic protein (GFAP). APP-like immunoreactive astrocytes exhibited strong labelling of the perinuclear cytoplasm and often possessed a long, fine process similar to that found with radial glia. The process extended to an APP-like immunoreactive meshwork in the RMS that consisted of cytoplasmic processes of astrocytes forming 'glial tubes'. Double-immunofluorescent labelling with a highly polysialylated neural cell adhesion molecule (PSA-NCAM) confirmed that the APP-like immunoreactive astrocytes in the SVZ and meshwork in the RMS made close contact with PSA-NCAM-immunopositive neuroblasts, suggesting an interaction between APP-containing cells and neuroblasts. This region of the adult brain is a useful in vivo model to investigate the role of APP in neurogenesis.     

Putrescine as an important source of GABA in the postnatal rat subventricular zone

The subventricular zone (SVZ) is a neurogenic region that continually gives rise to olfactory bulb (OB) GABAergic interneurons in mammals. The newly generated neuroblasts already express GABA while migrating to this structure along the rostral migratory stream (RMS). Here, we investigate in early postnatal rat if SVZ/RMS cells undertake the same synthetic pathway by which GABA is produced in differentiated neurons, i.e. the decarboxylation of glutamate by the glutamic acid decarboxylase (GAD), or, if an alternative pathway, the conversion of putrescine into GABA, also contributes to GABA synthesis. We show here that GAD immunoreactivity is not significantly detectable within the SVZ/RMS. However, strong immunolabeling is found within the OB. Nevertheless, low GAD enzymatic activity (as compared with OB) is detected in the SVZ/RMS. SVZ/RMS explants convert approximately 30% of all captured radiolabeled putrescine into GABA in vitro, showing that this pathway is important for GABA synthesis in the SVZ. We also show that SVZ/RMS, OB and choroid plexus explants are able to synthesize putrescine, as analyzed by ornithine decarboxylase (ODC) activity, providing neuroblasts with different sources of putrescine for GABA production. During early stages of neuroblast differentiation, in which neurotransmitter choice may still be undefined, an alternative pathway for GABA synthesis guarantees the production of GABA, necessary for neuroblast proliferation and migration in the SVZ/RMS.     

一种免疫荧光图像减影技术在鉴定drebrin E亚型的应用

目的:在缺乏drebrin E抗体的情况下利用一种新的免疫荧光计算机图像减影技术的方法鉴定drebrinE亚型。方法:应用drebrin非特异性抗体M2F6和drebrin A特异性抗体DAS2对成年大鼠脑冰冻切片进行双重免疫荧光染色,然后用计算机图像处理软件对同一切片的两种染色照片进行图像减影技术处理,观察drebrin E在成年大鼠脑中的分布情况。结果:通过免疫荧光计算机图像减影技术得到了drebrin E亚型的图像,确认了drebrin E在成年大鼠脑中吻侧迁移流、海马齿状回、梨状皮质的分布。结论:利用免疫荧光图像减影技术可以实现对drebrin E亚型的鉴定,为类似drebrin这样存在两种亚型的蛋白质鉴定提供了一种新的方法。     

Reelin调节小鼠喙端迁移流发育的形态学观察

目的 探讨小鼠室管膜下区（SVZ）的神经干细胞孵育成熟以及沿喙端迁移流（RMS）切线迁移至嗅球(OB)的过程,尤其是Reelin对细胞迁移和细胞分化的影响。方法 选用野生型（WT）小鼠50只和纯合reeler小鼠23只胚胎16 d至生后90 d的各年龄点小鼠大脑,应用尼氏染色、免疫荧光染色、墨汁灌注及电子显微镜技术标记并观察小鼠大脑的神经干细胞、胶质细胞以及血管发生之间的相互关系,比较两组小鼠RMS的发育情况。结果 胚胎后期至出生早期,在SVZ分布着大量的胶质细胞、神经干细胞和血管网,它们相互联系构成SVZ神经干细胞孵育的血管龛(niche);神经干细胞在niche中孵育成熟后可以进入RMS,切线迁移至嗅球,到达嗅球后转变为放射状迁移,分化为各种神经元整合入嗅球;神经干细胞在RMS的迁移过程中,放射状胶质细胞协同血管为其提供支架引导;reeler小鼠也能形成RMS,但形态有所改变,主要在嗅球处,神经干细胞失去规律排列,呈散乱分布。结论 室管膜下区的niche是神经干细胞的主要来源;血管协同放射状胶质细胞为RMS中的神经干细胞提供支架引导作用;作为调节细胞迁移的重要信号,Reelin可以通过其交互作用影响血管的发育,Reelin缺失导致嗅球处神经干细胞放射状迁移的转变障碍。     

Ionizing radiation enhances the engraftment of transplanted in vitro-derived multipotent astrocytic stem cells

The subependymal zone (SEZ) is a region of persistent neurogenesis in the adult mammalian brain containing a neural stem cell (NSC) pool that continuously generates migratory neuroblasts that travel in chains through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they differentiate and functionally integrate into existing neural circuitry. NSCs can be isolated from the SEZ and cultured to generate either neurospheres (NSs) or multipotent astrocytic stem cells (MASCs), with both possessing the stem cell characteristics of multipotency and self-renewal. NSs and MASCs home to the SEZ after transplantation into the lateral ventricle (LV) and contribute to neuroblast migration, with minimal engraftment into the OB observed in the adult mouse. Recent studies have compared the relatively uncharacterized NSC with the more established hematopoietic stem cell (HSC) in an effort to determine the level of stemness possessed by the NSC. Depletion of native HSCs in the bone marrow by lethal irradiation (LI) is necessary to maximize functional engraftment of donor HSCs. Our data show that the NSC pool and neuroblasts in the SEZ can be significantly and permanently depleted by exposure to LI. Attenuation of donor-derived migratory neuroblast engraftment into the OB is observed after transplantation of gfp+ MASCs into the LV of LI animals, whereas engraftment is significantly enhanced after transplantation into animals exposed to sublethal levels of ionizing radiation. By increasing receptiveness of the NSC niche through depletion of indigenous cells, the adult SEZ-RMS-OB can be used as a model to further characterize the NSC.     

Expression of ezrin in glial tubes in the adult subventricular zone and rostral migratory stream

Ezrin is a member of the ERM (ezrin-radixin-moesin) family of membrane-cytoskeletal linking proteins. ERM proteins are involved in a wide variety of cellular functions including cell motility, signal transduction, cell-cell interaction and cell-matrix recognition. A recent in situ hybridization study showed that the mRNA encoding ezrin is expressed in neurogenic regions of the mature brain including the subventricular zone (SVZ) and rostral migratory stream (RMS); however, the specific cell types expressing ezrin and their relationship to migrating and proliferating cells in these regions have not been characterized previously. In this study, we used immunocytochemistry to perform double labeling with a variety of cell-type specific markers to characterize the expression of ezrin in the SVZ and RMS of adult mice. Ezrin was expressed at high levels in both the SVZ and RMS where ezrin-immunopositive processes formed a trabecular network surrounding the proliferating and migrating cells. Ezrin-positive cells co-labeled with the glial makers S100beta and GFAP (glial fibrillary acidic protein), but only minimally with the early neuronal markers beta III tubulin and polysialylated form of neural cell adhesion molecule 1 (PSA-NCAM), indicating that ezrin was expressed primarily in the glial tube cells. Ezrin positive cells also expressed beta-catenin, a membrane-complex protein previously implicated in the regulation of stem-cell proliferation and neuronal migration. Glial tube cells act as both precursors of, and a physical channel for, migrating neuroblasts. Bi-directional signals between glial tube cells and migrating neuroblasts have been shown to regulate the rates of both proliferation of the precursor cells and migration of the newly generated neuroblasts. Our finding that ezrin and beta-catenin are both present at the cell membrane of the glial tube cells suggests that these proteins may be involved in those signaling processes.     

Disruption of Eph/ephrin signaling affects migration and proliferation in the adult subventricular zone

The subventricular zone (SVZ) of the lateral ventricles, the largest remaining germinal zone of the adult mammalian brain, contains an extensive network of neuroblasts migrating rostrally to the olfactory bulb. Little is known about the endogenous proliferation signals for SVZ neural stem cells or guidance cues along the migration pathway. Here we show that the receptor tyrosine kinases EphB1-3 and EphA4 and their transmembrane ligands, ephrins-B2/3, are expressed by cells of the SVZ. Electron microscopy revealed ephrin-B ligands associated with SVZ astrocytes, which function as stem cells in this germinal zone. A three-day infusion of the ectodomain of either EphB2 or ephrin-B2 into the lateral ventricle disrupted migration of neuroblasts and increased cell proliferation. These results suggest that Eph/ephrin signaling is involved in the migration of neuroblasts in the adult SVZ and in either direct or indirect regulation of cell proliferation.     

Conditional ablation of Tbr2 results in abnormal development of the olfactory bulbs and subventricular zone‐rostral migratory stream

Development of the olfactory bulb (OB) is a complex process that requires contributions from several progenitor cell niches to generate neuronal diversity. Previous studies showed that Tbr2 is expressed during the generation of glutamatergic OB neurons in rodents. However, relatively little is known about the role of Tbr2 in the developing OB or in the subventricular zone‐rostral migratory stream (SVZ‐RMS) germinal niche that gives rise to many OB neurons. Results: Here, we use conditional gene ablation strategies to knockout Tbr2 during embryonic mouse olfactory bulb morphogenesis, as well as during perinatal and adult neurogenesis from the SVZ‐RMS niche, and describe the resulting phenotypes. We find that Tbr2 is important for the generation of mitral cells in the OB, and that the olfactory bulbs themselves are hypoplastic and disorganized in Tbr2 mutant mice. Furthermore, we show that the SVZ‐RMS niche is expanded and disordered following loss of Tbr2, which leads to ectopic accumulation of neuroblasts in the RMS. Lastly, we show that adult glutamatergic neurogenesis from the SVZ is impaired by loss of Tbr2. Conclusions: Tbr2 is essential for proper morphogenesis of the OB and SVZ‐RMS, and is important for the generation of multiple lineages of glutamatergic olfactory bulb neurons. Developmental Dynamics 243:440–450, 2014. © 2013 Wiley Periodicals, Inc.     

Tenascin-R mediates activity-dependent recruitment of neuroblasts in the adult mouse forebrain

Neuroblasts arising in the adult forebrain that travel to the olfactory bulb use two modes of migration: tangentially, along the rostral migratory stream, and radially, in the core of the olfactory bulb where they start to ascend to the outer layers. Although the mechanisms of tangential migration have been extensively studied, the factors controlling radial migration remain unexplored. Here we report that the extracellular matrix glycoprotein tenascin-R, expressed in the adult mouse olfactory bulb, initiates both the detachment of neuroblasts from chains and their radial migration. Expression of tenascin-R is activity dependent, as it is markedly reduced by odor deprivation. Furthermore, grafting of tenascin-R-transfected cells into non-neurogenic regions reroutes migrating neuroblasts toward these regions. The identification of an extracellular microenvironment capable of directing migrating neuroblasts provides insights into the mechanisms regulating radial migration in the adult olfactory bulb and offers promising therapeutic venues for brain repair.     

Differential neurogenesis and gliogenesis by local and migrating neural stem cells in the olfactory bulb

The rostral migratory stream (RMS) is a unique forebrain structure that provides a long-distance migratory route for the neural stem cells of the periventricular region towards the olfactory bulb (OB). The purpose of the study presented here is to examine the extent of neurogenesis and gliogenesis by the neural stem cells of different origins (periventricular vs. intrabulbar) in the OB. After the RMS had been subjected to injury, the rats received intraperitoneal injections of 5-bromodeoxyuridine (BrdU) and were further reared for 2 weeks. Neuronal and glial differentiations of the BrdU(+) cells in the olfactory bulbar granule cell (OB-GCL) and the olfactory glomerular (OB-GL) layers were examined immunohistochemically using antibodies against neuronal (NeuN, neuronal nuclei) and glial (GFAP, glial fibrillary acidic protein) markers in the OBs with injured and uninjured (control) RMS. In the completely RMS-lesioned OB, where migration of the periventricular neural stem cells was inhibited, a small number of BrdU(+) NeuN(+) cells were found in both the OB-GCL and OB-GL. The BrdU(+) NeuN(+) cells accounted for a much higher percentage of the BrdU(+) cells on the control side (OB-GCL, 36.7%; OB-GL, 8.8%) than on the completely RMS-lesioned side (OB-GCL, 3.7%; OB-GL, 0.6%). The percentage of the BrdU(+) GFAP(+) cells relative to the BrdU(+) cells did not show any major difference between the control and completely RMS-lesioned sides. This study revealed differences in neurogenesis and gliogenesis between the local and migrating neural stem cells in the OB of the adult rodent.     

Multiphoton microscope imaging: The behavior of neural progenitor cells in the rostral migratory stream

Neural progenitor cells (NPCs) in the subventricular zone (SVZ) travel a long distance along the rostral migratory stream (RMS) to give rise to interneurons in the olfactory bulb (OB). Using the multiphoton microscope and time-lapse recording techniques we here report the behavior of NPCs in the RMS under both intact and ischemic conditions in living brain slices. The NPCs were visualized in 3-week-old transgenic mice that carry the reporter gene, green fluorescent protein (GFP), driven by the nestin promoter. Cortical brain ischemia was induced by permanent occlusion of the right common carotid artery and the middle cerebral artery. We observed that the RMS contained two populations of NPCs: nonmigrating cells (bridge cells) and migrating cells. Bridge cells enabled migrating cells to travel and also produced new cells in the RMS. The direction of NPC migration in the RMS was bidirectional in both intact and ischemic conditions. Cortical ischemia impeded NPC travel in the RMS next to the lesion area during the early period of ischemia. Cell–cell contact was a prominent feature affecting NPC translocation and migratory direction. These data suggest that behavior and function of nestin-positive NPCs in the RMS are variable. Cell–cell contacts and microenvironmental changes influence NPC behavior in the RMS. This study may provide insights to help in understanding NPC biology.     

Nucleotides and epidermal growth factor induce parallel cytoskeletal rearrangements and migration in cultured adult murine neural stem cells

Aim: The adult subventricular zone (SVZ) contains neural stem cells that generate neuroblasts migrating to the olfactory bulb (OB) and differentiating into interneurones. The molecular cues controlling essential functions within the neurogenesis pathway such as proliferation, short and long distance migration, functional integration and cell survival are poorly understood. We have previously shown that cultured adult neural stem cells express a considerable variety of nucleotide receptors and that nucleotides and epidermal growth factor (EGF) induce converging intracellular signalling pathways that carry potential for synergism in the control of neural stem cell proliferation and cell survival. Here we investigate the role of EGF and the nucleotides ATP, ADPβS and UTP in neural stem cell migration. Methods: Neural stem cells were prepared from adult mice and subjected to adherent culture. Labelling of F-actin was performed with tetramethylrhodamine isothiocyanate-phalloidin. Images were processed for quantitative evaluation of fluorescence labelling. Agonist-induced phosphorylation of AKT and focal adhesion kinase was analysed by quantitative Western blotting. Agonist-dependent cell migration was assayed using 48-well microchemotaxis chambers. Results: Nucleotides and EGF induce the formation of stress fibres, an increase in the cortical actin cytoskeleton and in cell spreading. This is associated with increased phosphorylation of AKT and focal adhesion kinase. Using microchemotaxis chambers we demonstrate a parallel increase in cell migration. Conclusion: Our results suggest that nucleotides and EGF acting as paracrine or autocrine signalling substances can be of relevance for structuring and maintaining the cytoarchitecture of the SVZ and the stream of neuroblasts migrating to the OB.     

Ionizing radiation induced long-term alterations in the adult rat rostral migratory stream

Ionizing radiation can induce significant injury to normal brain structures. To assess radiation-induced late effects, adult male Wistar rats received whole-body exposure with fractionated doses of gamma rays (a total dose of 4 Gy) and were investigated thirty, sixty and ninety days later. Immunohistochemistry and confocal microscopy were used to determine the density of neuroblasts derived from the anterior subventricular zone (SVZa) and brain resident microglia distributed along and/or adjacent to subventricular zone–olfactory bulb axis (SVZ–OB axis). Cell counting was performed in four anatomical parts along the well defined pathway, known as the rostral migratory stream (RMS) represented by the SVZa, vertical arm, elbow and horizontal arm of the RMS. Strong overdistribution of neuroblasts was seen in the SVZa thirty and sixty days after irradiation replaced by a steep decline in the following parts of the RMS and the highest decrease ninety days after radiation treatment along the entire SVZ–OB axis. Radiation treatment led to a decline or loss of microglia in almost all counted parts through the entire experiment. Results showed that ultimate decline of the SVZa descendants and loss of microglia suggests a contributory role of reduced neurogenesis in the development of radiation-induced late effects.     

Deprivation of sensory inputs to the olfactory bulb up-regulates cell death and proliferation in the subventricular zone of adult mice

The main olfactory bulb (MOB) is the first relay on the olfactory sensory pathway and the target of the neural progenitor cells generated in the subventricular zone (SVZ) lining the lateral ventricles and which migrate along the rostral extension of the SVZ, also called the rostral migratory stream (RMS). Within the MOB, the neuroblasts differentiate into granular and periglomerular interneurons. A reduction in the number of granule cells during sensory deprivation suggests that neurogenesis may be influenced by afferent activity. Here, we show that unilateral sensory deafferentation of the MOB by axotomy of the olfactory receptor neurons increases apoptotic cell death in the SVZ and along the rostro-caudal extent of the RMS. The vast majority of dying cells in the RMS are migrating neuroblasts as indicated by double Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick-end labeling/PSA-NCAM labeling. Counting bromodeoxyuridine-labeled cells in animals killed immediately or 4 days after tracer administration showed a bilateral increase in proliferation in the SVZ and RMS which was balanced by cell death on the operated side. These data suggest that olfactory inputs are required for the survival of newborn neural progenitors. The greatest enhancement in proliferation occurred in the extension of the RMS located in the MOB, revealing a population of local precursors mitotically stimulated following axotomy. Together, these findings indicate that olfactory inputs may strongly modulate the balance between neurogenesis and apoptosis in the SVZ and RMS and provide a model for further investigation of the underlying molecular mechanisms of this activity-dependent neuronal plasticity.     

Dynamic imaging reveals that brain-derived neurotrophic factor can independently regulate motility and direction of neuroblasts within the rostral migratory stream

Neuronal precursors generated in the subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Although, the mechanisms regulating this migration remain largely unknown. Studies have shown that molecular factors, such as brain-derived neurotrophic factor (BDNF) emanating from the OB, may function as chemoattractants drawing neuroblasts toward their target. To better understand the role of BDNF in RMS migration, we used an acute slice preparation from early postnatal mice to track the tangential migration of GAD65-GFP labeled RMS neuroblasts with confocal time-lapse imaging. By quantifying the cell dynamics using specific directional and motility criteria, our results showed that removal of the OB did not alter the overall directional trajectory of neuroblasts, but did reduce their motility. This suggested that additional guidance factors present locally within the RMS region also contribute to this migration. Here we report that BDNF and its high affinity receptor, tyrosine kinase receptor type 2 (TrkB), are indeed heterogeneously expressed within the RMS at postnatal day 7. By altering BDNF levels within the entire pathway, we showed that reduced BDNF signaling changes both neuroblast motility and direction, while increased BDNF levels changes only motility. Together these data reveal that during this early postnatal period BDNF plays a complex role in regulating both the motility and direction of RMS flow, and that BDNF comes from sources within the RMS itself, as well as from the olfactory bulb.     

Genetic disruption of the alternative splicing of drebrin gene impairs context-dependent fear learning in adulthood

Dendritic spines are postsynaptic structures at excitatory synapses that play important roles in synaptic transmission and plasticity. Dendritic spine morphology and function are regulated by an actin-based cytoskeletal network. Drebrin A, an adult form of drebrin, is an actin-binding protein in dendritic spines, and its decrease is purportedly concerned with synaptic dysfunction in Alzheimer's disease. Rapid conversion of drebrin E, an embryonic form of drebrin, to drebrin A occurs in parallel with synaptic maturation. To understand the physiological role of drebrin isoform conversion in vivo, we generated knockout mice in which a drebrin A-specific exon was deleted from the drebrin gene. Drebrin A-specific knockout (DAKO) mice expressed drebrin E, which substituted for drebrin A. Subcellular fractionation experiment indicated that cytosolic form of drebrin was increased in the brains of DAKO mice. Furthermore, drebrin accumulation in synaptosomes of DAKO mice was much higher than that of wild-type (WT) mice. DAKO mice were viable and showed no apparent abnormalities in their gross brain morphology and general behaviors. However, DAKO mice were impaired in a context-dependent freezing after fear conditioning. These data indicate that drebrin A plays an indispensable role in some processes of generating fear learning and memory.     

嗅球切除对成年大鼠侧脑室外侧壁新生细胞增殖和分化的影响

目的 研究嗅球切除后成年大鼠侧脑室外侧壁(SVZ)新生细胞增殖和分化的情况,进一步探讨嗅球对SVZ神经生发活动的影响.方法 建立成年SD雄性大鼠右侧嗅球切除模型,并分别存活4周和12周,利用Nissl染色、多唾液酸神经细胞黏附分子(PSA-NCAM)和BrdU免疫组织化学染色的方法观察了成年SD大鼠嗅球切除后存活不同时间两侧吻侧迁移流(RMS)BrdU阳性细胞数占总细胞百分比的变化以及两侧RMS PSA-NCAM阳性细胞的形态学变化.结果 1.嗅球切除后不同时间点,嗅球切除侧RMS的细胞数增加,BrdU免疫阳性细胞数增加,但BrdU免疫阳性细胞数占总细胞数的百分比随嗅球切除后大鼠存活时间的延长而下降,且以RMS的吻侧部分下降更明显;2.嗅球切除后,在切除侧断端吻侧颗粒层和RMS均出现较对照侧更多的具有较长突起的PSA-NCAM阳性细胞.结论 嗅球切除后仍有新生神经元沿RMS向吻侧迁移,但其增殖率随时间延长下调;嗅球的切除似乎并没有影响成神经细胞的分化.