Anatomy of the brain neurogenic zones revisited: fractones and the fibroblast/macrophage network

Cytogenesis in adult peripheral organs, and in all organs during development, occurs nearby basal laminae (BL) overlying connective tissue. Paradoxically, cytogenesis in the adult brain occurs primarily in the subependymal layer (SEL), a zone where no particular organization of BL and connective tissue has been described. We have reinvestigated the anatomy of the area considered the most neurogenic in the adult brain, the SEL of the lateral ventricle, in zones adjacent to the caudate putamen, corpus callosum, and lateral septal nucleus. Here, we report structural (confocal microscopy using laminin as a marker) and ultrastructural evidence for highly organized extravascular BL, unique to the SEL. The extravascular BL, termed fractones because of their fractal organization, were regularly arranged along the SEL and consisted of stems terminating in bulbs immediately underneath the ependyma. Fractones contacted local blood vessels by means of their stems. An individual fractone engulfed in its folds numerous processes of astrocytes, ependymocytes, microglial cells, and precursor cell types. The attachment site (base) of stems to blood vessels was extensively folded, overlying large perivascular macrophages that belong to a fibroblast/macrophage network coursing in the perivascular layer and through the meninges. In addition, collagen-1, which is associated with BL and growth factors during developmental morphogenetic inductions, was immunodetected in the SEL and particularly regionalized within fractones. Because macrophages and fibroblasts produce cytokines and growth factors that may concentrate in and exert their effect from the BL, we suggest that the structure described is implicated in adult neurogenesis, gliogenesis, and angiogenesis.     

单侧海马损毁诱发双侧齿状回细胞增殖的研究

目的探讨成年大鼠单侧海马锥体细胞被损毁后,海马齿状回(dentategyrus,DG)神经干细胞/前体细胞(neuralstemcells/progenitorcells)原位激活的时间变化规律。方法用海人酸(kainicacid,KA)建立单侧海马损毁模型,用5溴脱氧尿嘧啶核苷(5bromodeoxyuridine,BrdU)标记增殖的细胞,免疫组织化学染色检测损毁后不同时间点损毁侧及对侧海马DG表达BrdU的细胞数。结果空白对照组和各时间点假损毁组双侧海马DG区均可见到少量BrdU阳性细胞,组间无显著性差异(P>0.05);与对照组比较,实验组双侧DGBrdU阳性细胞均于损毁后第3d起明显增多(P<0.01),第5d达高峰(P<0.01),第9d下降至对照组水平;损毁侧阳性细胞数目较对侧略多。结论成年大鼠单侧海马损毁可增强双侧海马DG的神经发生,其机制可能与损毁引起的机体激素水平、神经递质、神经营养因子浓度的改变以及损毁侧局部微环境变化有关。     

局灶性脑缺血后室管膜/室下区细胞迁移到梗塞区周围并分化为神经元和星形胶质细胞

目的研究局灶性脑缺血后室管膜/室下区细胞的迁移分化,揭示梗塞区周围新生细胞的来源.方法大脑中动脉阻塞前,将10μl 0.2%的荧光染料DiI注射于体质量250～350 g的雄性SD大鼠侧脑室以预标记室管膜/室下区细胞.脑缺血后,采用累积式的BrdU标记方法标记新生细胞并通过双重免疫荧光染色确定细胞分化.标记的细胞通过激光共聚焦显微镜观察.结果在非缺血对照大鼠,DiI标记细胞定居于室管膜/室下区.局灶性脑缺血后,DiI标记细胞出现于胼胝体,邻近的纹状体和皮质.此外,缺血14 d后,梗塞区周围纹状体和皮质内可见一些DiI/BrdU/GFAP或DiI/BrdU/NeuN三重标记阳性细胞.结论局灶性脑缺血后,室管膜/室下区细胞迁移到梗塞区周围并分化成神经元和星形胶质细胞,这一发现对于理解成体神经干细胞的起源和开发促进脑损伤后内源性神经发生的新措施具有重要意义.     

nNOS选择性拮抗剂7-硝基吲唑促进成年小鼠脑缺血后神经元再生

目的研究nNOS选择性拮抗剂7-硝基吲唑对脑缺血后神经元再生的影响。方法大脑中动脉阻塞法制备局灶性脑缺血/再灌注模型。腹腔注射7-硝基吲唑(30 mg.kg-1)。B rdU、NeuN标记法测定海马齿状回的细胞扩增及新生细胞的分化,跳台实验法测定动物的学习记忆能力。结果在脑缺血后d 8缺血侧海马齿状回的B rdU阳性细胞数比对照侧多大约3倍,7-硝基吲唑进一步促进了脑缺血所诱发的海马齿状回神经细胞扩增,并促进新生细胞的存活,改善脑缺血小鼠的学习记忆功能。结论nNOS对脑缺血诱发的海马齿状回神经元再生有重要作用。     

BrdU/NeuN双标记法研究复方刺蒺藜苷抗抑郁的机制

目的：观察复方刺蒺藜苷对慢性应激抑郁大鼠海马神经元发生的影响,并探讨其机理。方法：采用慢性应激加孤养建立大鼠抑郁模型,通过敞箱实验等观察抑郁模型大鼠行为学改变,BrdU/NeuN标记海马齿状回阳性细胞反映神经元发生,分化。结果：慢性应激抑郁大鼠体重增长缓慢,蔗糖溶液消耗量减少,敞箱实验中水平穿越格数、竖立次数、理毛时间减少,中央格停留时间、粪便粒数均增加,与正常组比较具有显著性差异（P〈0.05或P〈0.01）。复方刺蒺藜苷和氟西汀可改善大鼠行为学变化,增加BrdU/NeuN阳性细胞数,与模型组比较具有显著性差异（P〈0.05或P〈0.01）。结论：复方刺蒺藜苷能明显改善抑郁大鼠的各项行为学指标,促进海马神经元发生,具有抗抑郁作用。     

基因芯片分析Wnt刺激后小鼠多潜能分化干细胞C3H10T1/2的差异基因表达

目的 探讨Wnt信号传导系统对诱导干细胞向神经系统分化的基因表达的影响.方法 采用最新的含有22000多个已知基因及EST克隆的小鼠基因芯片U74Av2,检测了Wnt刺激后的小鼠多潜能分化干细胞C3H10T1/2中目标基因表达的变化,并进行实时定量PCR,验证了基因芯片结果.结果 Wnt刺激后小鼠多潜能分化干细胞C3H10T1/2中Wnt信号传导系统各主要组成基因表达有不同程度增加;对干细胞向神经系统发育有潜在调节作用的基因表达也有增加或减少.结论 表达谱芯片分析成功筛选出wnt刺激引起表达改变且可能与神经发生有关的基因.     

Ultrastructural characterization of synaptic terminals formed on newly generated neurons in a song control nucleus of the adult canary forebrain

The fine structure of synaptic terminals contacting neurons generated in the forebrain of adult male canaries was investigated by autoradiography and electron microscopy. The procedure for labeling the new neurons included pretreating adult canaries with 3H-thymidine and sacrificing them 23-45 days later. Neurons were identified as newly generated by the presence of 3H-thymidine in the cell nucleus. The new neurons in the nucleus hyperstriatum ventralis, pars caudalis (HVc) were identified by autoradiography and light microscopy and examined with electron microscopy. Several types of synaptic terminals contacted the cell body and proximal dendrites of the newly formed neurons. Synaptic junctions were formed by terminals that contained spherical, agranular vesicles, large dense-core vesicles and spherical, agranular vesicles, and pleomorphic or flattened synaptic vesicles. Terminals that contained spherical vesicles were most often associated with asymmetric synaptic densities, and terminals that contained pleomorphic or flattened vesicles formed symmetric junctions. New neurons were also contacted by small terminals that contained few vesicles and had little pre- or postsynaptic density associated with the junction; these terminals may be a special type or may be in the process of developing their synaptic contact with the new neuron. In addition, rare terminals that appeared to be degenerating or to contain debris from other degenerating neural elements contacted new neurons. In summary, these data indicate that the new neurons, which are known to be inserted into existing neural networks, receive synaptic input from at least three different sources.     

Où sont donc passées les cellules-souches neuronales de la couche sous-épendymaire chez l’être humain ?

Stem cells are characterized by their ability for self-renewal (allowing them to be present throughout the entire life of the organism) and their ability to give rise to differentiated cells belong to one or more lineages. The strict definition of these cells is however still a matter of debate. There is new experimental evidence (including in human beings) that stem cells are present within the brain and may give rise to neurons. Ependymal cells have been proposed to play such a role. In fact, subependymal cells expressing GFAP would be more likely candidates. Such cells are observed in the brain of human beings. They are able to differentiate into neurons in vitro but such potential appears to be repressed in vivo.