第5章中枢神经系统发育及其可塑性

1、Development of Central Nervous System and Its Plasticity诱导诱导(induction) ：指胚胎发育过程中两种细胞群落通过分子间的相互作用使其中一个群落或两个群落发生定向分化的过程。提供或传递诱导分子的细胞是诱导者( inductor)，接受这种分子的细胞或结构称反应者( reactor)。结构发育：结构发育：神经上皮脑和脊髓构筑神经环路发育或构筑：神经环路发育或构筑：神经元发生突触形成可塑性可塑性(plasticity)：即神经系统发育过程中神经元对神经活动及环境改变所作出的结构和功能上的应答反应。细胞调亡 - 突触重排及消退等Outl

2、ine Ectoderm - neural tube - brain and spinal cord (review) The genesis of neurons The genesis of connections (synapse formation) The elimination of cells and synapses Activity-dependent synaptic rearrangement The Elementary Mechanisms of Cortical Synaptic Plasticity Importance of the critical perio

3、d Concluding RemarksFrom neural tube to the initial brain and spinal cord The entire nervous system arises from the ectoderm The induction and patterning of the nervous system (A)神经板期(B)神经褶期 (C) 神经管期脊椎动物脊椎动物神经管神经管的形成的形成: :神经管有两个主要的轴线：背腹轴背腹轴和头尾轴头尾轴。前后轴将神经系统分成前脑、中脑、后脑和脊髓，还将这些区域细分为更加特殊的神经结构。在背腹轴上，不同的区域

4、也有不同的神经细胞种类。在有些部位，还有左右轴，即左右两侧分布不同的神经细胞。外周神经系统来源于与神经板相邻的神经脊神经脊，后者是外胚层中一群特殊的细胞，从发源地迁移到胚胎多个部位，形成包括外周神经系统在内的多种组织。即脊髓平面的神经系统及其周围组织，背侧在上，腹侧在下。- The neural plate is induced by signals from adjacent mesoderm- The neural plate is patterned along its dorso-ventral axis by signals from adjacent non-neural cell

5、s The ventral NT the notochord The dorsal NT the epidermal ectoderm The neural tube (NT) formationneural plateneural grooveneural foldneural tubeneural tubeCranial neuroporeCranial neuropore anlage brainanlage brainanlage spinal cordanlage spinal cordCaudal neuroporeCaudal neuroporeCNS The neural tu

6、be formation 三个原始脑泡是脑的原基三个原始脑泡是脑的原基 前脑泡前脑泡中脑泡中脑泡菱脑泡菱脑泡 （后）（后）前前N N孔闭合孔闭合脑脑 泡泡Brain Brain vesiclevesicle端脑端脑 间脑间脑后脑后脑末脑末脑第三脑室第三脑室左、右大脑半球左、右大脑半球两个侧脑室两个侧脑室背：四叠体背：四叠体腹：大脑脚腹：大脑脚 中脑中脑脑桥、小脑脑桥、小脑延髓延髓脑泡腔脑泡腔第四脑室第四脑室中：中脑导水管中：中脑导水管基基本本保保持持三三层层结结构构边缘层边缘层白质白质套层套层脊髓灰质脊髓灰质管腔管腔中央管中央管两侧壁套层神经母细胞和成胶质细胞的迅速增生而增厚两侧壁套层神经母细

7、胞和成胶质细胞的迅速增生而增厚神经管顶壁和底壁薄而窄神经管顶壁和底壁薄而窄 神经管的尾侧段分化、发育为脊髓神经管的尾侧段分化、发育为脊髓腹侧腹侧两基板两基板背侧背侧两翼板两翼板顶顶 板板底底 板板 胚胎第三个月之前，脊髓与脊胚胎第三个月之前，脊髓与脊 柱等长，其下端达脊柱的尾骨；柱等长，其下端达脊柱的尾骨； 胚三个月后，因脊柱增长快于胚三个月后，因脊柱增长快于 脊髓，脊柱便渐超越脊髓向尾脊髓，脊柱便渐超越脊髓向尾 端延伸，脊髓位置相对上移；端延伸，脊髓位置相对上移； 出生前，脊髓下端与第三腰椎出生前，脊髓下端与第三腰椎 平齐，仅以终丝与尾骨相连；平齐，仅以终丝与尾骨相连； 节段分布的脊神经均在

8、胚胎早节段分布的脊神经均在胚胎早 期形成，从相应节段的椎间孔期形成，从相应节段的椎间孔 穿出，脊髓位置上移后，脊髓穿出，脊髓位置上移后，脊髓 颈段以下的脊神经根便斜向尾颈段以下的脊神经根便斜向尾 侧，至腰、骶、尾段的脊神经侧，至腰、骶、尾段的脊神经 根则在椎管内垂直下行，与终根则在椎管内垂直下行，与终 丝共同组成马尾。丝共同组成马尾。Normal Anencephaly spinal bifida 发育异常是指由于各种因素导致的先天畸形。发育异常是指由于各种因素导致的先天畸形。狭义狭义的概念的概念仅指出生时解剖结构畸形。仅指出生时解剖结构畸形。广义广义的包括出生时各种解剖结的包括出生时各种解剖

9、结构畸形、功能缺陷及代谢、遗传行为的发育异常。构畸形、功能缺陷及代谢、遗传行为的发育异常。 据据WHO(1966) WHO(1966) 调查了包括调查了包括1616个国家的个国家的2525个医学中心的个医学中心的421421 781781次妊娠，发现严重畸形占次妊娠，发现严重畸形占0.46%0.46%，轻度畸形占，轻度畸形占1.27%1.27%，总发生率为总发生率为1.73%1.73%。 我国我国1986-19871986-1987年作为国家攻关课题进行了大规模的出生缺年作为国家攻关课题进行了大规模的出生缺陷调查，对全国陷调查，对全国2929个省市自治区的个省市自治区的945945所医院所医院

10、124124万多围产万多围产儿进行了监测，发现出生缺陷的总发生率平均为儿进行了监测，发现出生缺陷的总发生率平均为1.301%1.301% 一些流行病学调查结果显示某些出生类型的缺陷，发生率一些流行病学调查结果显示某些出生类型的缺陷，发生率与地理条件有密切关系。山西省出生缺陷总发生率最高，与地理条件有密切关系。山西省出生缺陷总发生率最高，湖北省最低湖北省最低 中枢神经系统发育异常并不少见中枢神经系统发育异常并不少见 中枢神经系统畸形绝大部分是由于神经管发育缺陷或神经管中枢神经系统畸形绝大部分是由于神经管发育缺陷或神经管前后孔未闭引起前后孔未闭引起, ,占总先天畸形发病率的占总先天畸形发病率的17

11、17. .主要是无脑畸主要是无脑畸形、隐性脊柱裂、脊髓脊膜膨出，脑积水等。此外，脑过小形、隐性脊柱裂、脊髓脊膜膨出，脑积水等。此外，脑过小畸形、胼胝体不发育、苯丙酮尿症、精神发育迟滞等均属神畸形、胼胝体不发育、苯丙酮尿症、精神发育迟滞等均属神经系统的发育异常，但较少见。经系统的发育异常，但较少见。 遗传因素：包括单基因遗传性疾患，多基因遗传性疾患及染遗传因素：包括单基因遗传性疾患，多基因遗传性疾患及染色体病；色体病； 环境因素：包括药物和环境化学物质、微生物感染、电离辐环境因素：包括药物和环境化学物质、微生物感染、电离辐射、母体疾病等因素。此外，营养因素如已知某些维生素缺射、母体疾病等因素。此

12、外，营养因素如已知某些维生素缺乏，特别是叶酸缺乏可影响神经管的正常封闭。乏，特别是叶酸缺乏可影响神经管的正常封闭。 导致发育畸形的因素远未完全清楚导致发育畸形的因素远未完全清楚- The first step in wiring the nervous system together is the generation of neurons. - Neuronal structure develops in three major stages: 1. Cell proliferation2. Cell migration 3. Cell differentiation The genesis

13、 of neuronsInducting factorsmesodermNeuronal progenitorGlial progenitorNeural progenitorectoderm1. cell proliferation - Induction during neuronal genesis背唇可以诱导两栖类动物胚胎形成第二条神经轴：（A）斯佩曼和曼葛得的组织块移植实验。将供体原肠胚早期的背唇移植到宿主胚胎的腹侧以后，宿主会在应该形成腹部表皮的位置，产生包括神经板在内的第二个体轴。(B) 神经诱导的分子模型。背唇中胚层细胞分泌的NogginNoggin、ChordinChordi

14、n和和FollistatinFollistatin能阻止阻止外胚层中的BMPBMP家族蛋白与其受体结合，从而抑制BMP诱导表皮的产生，使背侧外胚层形成神经板。原肠胚期早期的两栖类动物胚胎原肠胚期早期的两栖类动物胚胎中胚层细胞能决定神经系统的前后轴中胚层细胞能决定神经系统的前后轴 （A）原肠胚期晚期的两栖类动物胚胎的组织结构（前后轴中线水平的切面）；（B）用于解释神经板如何沿着前后轴分化的“双信号”假说。 Where are neuron and glial cell from?glioblastNeural tube-MSCNeural-epitheliaNeuroblast 1. cell

15、proliferation - To grow or multiply by rapidly producing new cellsneural tubeVentricular zoneMarginal zoneNeuroblastneural tube1. cell proliferation - a characteristic of the choreography of cell proliferation Both daughter cells cleaved vertically from the precursor remain in the ventricular zone t

16、o divide again and again. This mode of cell division predominates early in development expand the population of neuronal precursor The both cells cleaved horizontally from the precursor, one migrates away to take up its position in the cortex, where it will never divide again. The other daughter rem

17、ains in the ventricular zone to undergo more division. This mode predominates later in development neuronal precursor1. cell proliferation - The fate of the newly formed daughter cellsVentricular zone precursor cells repeated this pattern until all of the neurons of the cortex have been generated. T

18、he cleavage have been basically finished on pregnant fifth month in human.In human, most neocortical neurons are born between the fifth week and fifth month of gestation (pregnancy), peaking at the astonishing rate of 250,000 new neurons per minute.Research suggest: the gene expression of the precur

19、sor is regulated by its transcription factors( the proteins/upstream molecules ). See left figure. Notch-1 “unopposed” by numb, activates the gene expression that the cell to cease division and migrate away from the ventricular zone.1. cell proliferation - How does the cleavage plane during cell div

20、ision determine the cells fate? - The distribution of cell constituents in precursor cells:Notch介导的信号传导通路细胞之间可以通过对话来选择不同的命运介导的信号传导通路细胞之间可以通过对话来选择不同的命运（A）在果蝇的正常发育过程中，一个形成中的神经前体细胞（深绿色）能阻止阻止邻近的神经外胚层细胞（浅绿色）也选择这一命运，使后者变成表皮细胞（白色）（B）形成中的神经前体细胞通过Delta来激活邻近的细胞中的Notch信号传导通路，从而抑制抑制AS-C和Delta等基因的表达，使邻近的细胞不能成为神经

21、前体细胞（C）Notch活性的改变能影响果蝇神经前体细胞的数量不对称细胞分裂可以造成细胞的多样性不对称细胞分裂可以造成细胞的多样性 （A）Numb蛋白的不对称分布可以使两个子细胞选择不同命运。集中在细胞一侧的Numb蛋白（绿色）是否只分配给一个子细胞，还取决于纺锤体（粉红色）的位置，即细胞分裂的平面（橙色）（B）果蝇的SOP细胞通过三轮不对称的分裂产生组成感受机械或化学信息的外感觉（ ES）器官的四个细胞。Numb缺失或对称分布都会影响ES器官的形成（C）Notch活性的改变也会影响ES器官的形成。H: 刚毛细胞；N：感觉神经元；S: 毛孔细胞；Sh，鞘细胞。转录因子的按顺序表达使神经母细胞每

22、次分裂后产生不同的神经元转录因子的按顺序表达使神经母细胞每次分裂后产生不同的神经元 （A A）在最早几次分裂时，果蝇所有）在最早几次分裂时，果蝇所有的神经母细胞都会按顺序表达四个转的神经母细胞都会按顺序表达四个转录因子录因子（B B）HbHb和和KrKr缺失或持续表达能影响缺失或持续表达能影响神经母细胞产生不同神经母细胞产生不同GMCGMC的能力。虚的能力。虚线显示线显示GMCGMC或者死亡，或者变成二生或者死亡，或者变成二生（HbHb缺失）或头生（缺失）或头生（KrKr缺失）缺失）GMCGMC（C C）、和这三）、和这三个神经母细胞每次分裂后产生的个神经母细胞每次分裂后产生的GMCGMC各不

23、相同，但用同样的转录因子来决各不相同，但用同样的转录因子来决定它们的命运。和前两定它们的命运。和前两次分裂时都表达次分裂时都表达HbHb。只分裂三。只分裂三次。运动：运动神经元；中间：中间次。运动：运动神经元；中间：中间神经元；胶质：胶质细胞神经元；胶质：胶质细胞（D D）神经母细胞和）神经母细胞和GMCGMC分裂时也将分裂时也将NumbNumb蛋白不对称地分配给两个子细胞。蛋白不对称地分配给两个子细胞。GMCGMC只分裂一次，产生两个不同的神只分裂一次，产生两个不同的神经细胞，并通过经细胞，并通过NumbNumb的不对称分布使的不对称分布使它们选择不同的命运它们选择不同的命运Neurogen

24、esis in the adult neocortexRecent finding show:1.Although most of the division action is over well before birth, the adult SGZ and SVZ retains some capacity to generate new neuron. 2.Behavior/functional activity and environment 3.Neurogenesis in the adult brain is far too limited to repair CNS damag

25、e.2. Cell migration-The daughter cells from the precursors that immature neuron are called Neuroblast.- A scaffold for the migration provided by the radial glial cells.- the first migration neuroblasts away from the ventricular form the cortical plate.- This shows neuroblasts crawling along the thin

26、 processes of the radial glia route to the cortical plate, which forms just under the marginal zoneA migrating cell recorded in tissue cultureA:神经细胞迁移过程中,有领先突起。领先突起有分枝,动态竞争,其中一枝成为主干,带领细胞体的移动,其后,又不断重复分枝竞争,决定细胞移动方向。B:迁移的神经细胞也可以原来领先突起的生长锥消失,在细胞体完全相反的一边长处出新的突起,导致细胞180度转向。迁移的神经细胞:AB鼠脑SVZ细胞：肌动蛋白丝染绿色绿色微管红色

27、 - Inside-out development of the cortex - the first cells to migrate to cortical plate from VZ that form subplate - As these differentiate into neurons become layer VI in the cortical plate. - this process repeats again and again until all layers of the cortex the sublate neurons disappear 较早分化的较大神经

28、元先迁移并形成最内层，依次顺序向外；而较晚分化的较小神经元则通较早分化的较大神经元先迁移并形成最内层，依次顺序向外；而较晚分化的较小神经元则通过已形成的层次迁移并形成其外侧新的层次；过已形成的层次迁移并形成其外侧新的层次；故不论皮质的什么区域，其最内层总是最早分故不论皮质的什么区域，其最内层总是最早分化，而最外层则最后分化。化，而最外层则最后分化。哺乳动物大脑新皮层功能区域的形成哺乳动物大脑新皮层功能区域的形成 （A）在正常发育过程中，胚胎前脑背部中线和头端的成型中心分泌BMP、Wnt和FGF8等因子，使这些蛋白分别沿背腹轴和前后轴形成浓度梯度，进而影响多种转录因子在神经前期细胞中的表达量，最

29、终把大脑新皮层分化成不同的功能区域。（B）受在胚胎前脑后端异位表达的FGF8影响，大脑新皮层能在后端形成第二个运动和躯体感觉皮层。 3. Cell differentiation- The process in which a cell take on the appearance and characteristics of a neuron is known as cell differentiation. Differentiation is the consequence of a specific spatiotemporal pattern of gene expression.-

30、 Differentiation of the neuroblast into a neuron begins with the appearance of neurites sprouting off the body (all same axon and dendrite at first). The differentiation is programmed well before the neuroblast arrives at its final resting place. The complexity of dendritic tree is not entirely prep

31、rogrammed.- The fine structure of axons and dendrites also depends on “environmental” factors in the cortex. 3.1 Differentiation of cortical areasNiss-staineda. position of the major vibrissae on the faceb. vibrissae region of S1c. Barrels in S1- A somatotopic map of the facial vibrissae on mouse ce

32、rebral cortex 在决定神经细胞命运的过程中，细胞之间的相互作用起重要作用。这些相互作用既可以发生于神经细胞与非神经细胞之间，也可以发生于神经细胞之间；这些相互作用既可以通过弥散在环境中的诱导因子，也能通过细胞之间的直接对话。 细胞外的因子最终会在细胞内激活一个特异的分裂和分化程序，使神经前体细胞可以在很大程度上不受环境的影响，产生不同的神经细胞。通过对这些机理的进一步的研究，发育神经生物学的最终目标是能够精确地描述：在发育过程中，不同的神经元和胶质细胞如何按准确的数量、在特定的时期、在不同的神经系统部位产生。 Genesis of connection / synapse form

33、ationLM:Model (chemical synapse )Review：definition, classify, structureEM:Genesis of connection: for example1. The three phases of pathway formation Pathway selection path target selection structure address selection cellThe three phases depends on :1. Direct cell-to-cell contract2. contract between

34、 cells and extracellular secretions of other cell3. communication via action potentials and synaptic transmission About 100 billion neurons in brain - remarkably precise interconnection among them - to perform the functions of the brain.1. The growing axonThe growing tip of a neurite is called a gro

35、wth cone, which is specialized to identify an appropriate path for neurite elongation.Structure and feature of growth cone:- probe the environment, moving in and out of the lamellipodia- takes hold of the substrate and pull the advancing GC forward Growth cone in cultureFasciculationCell adhesion mo

36、lecules (CAMs)“highway” 2. Axon guidance and guidance cuesTarget cellExtracecular molecularsSpecial bindingSeconde messengerFunction changes of microbubules and actin within growth coneControlling growth cone extendingGuidance cues: chemoattraction and actins concentrate in forepart of a GC chemorep

37、ulsion and actins disappear in forepart of a GCMembrane receptorsChemoattraction and chemorepulsion Netrin spurs the axon growth toward the midlineThe receptors of Netrin and Slit are be regulated in varying from one side of the midline to other Pushpull Slit chase the axon away the midline神经管沿背腹轴的分

38、化神经管沿背腹轴的分化 （A）Shh和BMP家族蛋白分别在脊髓腹侧与背侧形成浓度梯度，从而使神经前期细胞在背腹轴不同的位置选择不同的命运。Shh由脊索和底板分泌，而BMP则由表皮（神经管形成之前）或顶板（神经管形成之后）分泌。（B）神经管沿背腹轴分化的分子模型。Shh抑制I型HD蛋白的表达，但激活II型HD蛋白的表达。I型和II型HD蛋白能抑制彼此的表达，但它们在腹侧的不同位置有不同的表达范围，形成HD蛋白编码，从而共同分化神经前期细胞，使后者只能产生某一种神经元。 3. Synapse formation- When the growth cone comes in contact with

39、 its target, a synapse is formed.- The details of mechanisms of synapse formation in the CNS are still sketchy, - Most of the data comes from studies of the neuromuscular junction. Exp. Steps in the formation of a NMJ: 1. The GMN terminal secretes agrin, (Ca+ entry into the GC triggers neuro- transm

40、itter release and changes in the cytoskeleton adhere to its post- synapse partner) 2. Agrin interacts with MuSK in the muscular cell membrane. 3. The clustering of Ach receptors in the postsynaptic membrane via the action of rapsyn (like a shepherd to gather the receptors at the synapse)Ca+ Nerve gr

41、owth factor (NGF), a peptide was the first trophic factor tobe identified in 1940s by Italian biologist Rita Levi-Montalcini. If injecting antibodies of NGF into postsynaptic tissue or axoplasmic transport is disrupted the neurons die. (the work earned levi-montalcini and Cohen the 1986 Nobel Prize)

42、 Family members of Neurotrophic Factors include: NGF, NT-3, NT-4 and BDNF (brain derived neurotrophic factor). PCD is actually a consequence of genetic instructions to self-destruct by a process called apoptosis.Why dont axon regenerate in our CNS?The critical difference seems tobe the different env

43、ironments of the CNS and PNS. In the early 1980s, Albert Aguaya et al. at Montreal General Hospital tested this idea in very important experiment showed as Fig A.Martin Schwab et al. in Zurich university demonstrated that CNS neurons grown in tissue culture extend axons along substrates prepared fro

44、m Schwann cells but not from oligodendroglia. This finding led to the search for glial factors that inhibit axon growth in the CN, and a molecule called nogo was finally identified early in 2000.Anti-nogo antibody calle IN-1 has been raised, them injected the aitibody into adult rats after spinal co

45、rd injury. This treatment enabled about 5%of the severed axons to regenerate Fig A1.Cell death Entire populations of neurons are elimited during pathway formation, a process known as Programmed cell death (PCD). Matching inputs with targets by selective cell death. The input neurons will compete wit

46、h one another for limited quantities of trophic factors produced by the target neurons.A cell transfiguration away from adhesion surface Nucleus ruptureNucleus concretion and dwindle in sizeNucleus crumbleCell membrane entad-sunkenForming apoptosis bodyForming half-moonChromatin concentrate edge of

47、nucleus membranephagocytosis by phagocyte or macrophage Biological feature for apoptosis or PCD M 1 2 3 4 5 6EMApoptosis or PCD2. Changes in synaptic capacity Each neuron can receive on its dendrites and soma a finite number of synapses called synaptic capacity peaks early in development and then de

48、clines. Especially in adolescent of macaque monkey in visual cortical declined by mostly 50 %, 5000 per second. A useful model system for the study of synaptic elimination: effect of postsynaptic AChR, basal membrane of muscular fibril on neuromuscular synaptic elimination.1. Synaptic segregation (分

49、离)a. The two input neurons in one eye (top) fire at the same time this is sufficient to cause the top LGN target neuron to fire but not the bottom one. b. This is the same situation as in part a, except that now the two input neurons in the other eye (bottom) are active simultaneously, causing the b

50、ottom target neuron to fire.c. Over time, neurons that fire together wire together. Notice also that input cells that fire out of sync with the target lose their link.视顶盖对应投射机理：视顶盖对应投射机理：顶盖有内高外低的Wnt3梯度，其排斥性受体Ryk在视神经呈腹侧高背侧低的梯度，其吸引性受体Fzl均匀分布于视神经腹背轴线。 （A）鼻颞视轴突依赖EphA介导的ephrinA排斥信号，EphA以鼻侧高颞侧低的梯度存在于视网膜，而

51、其配体ephrinA以梯度形式存在于顶盖（B）背腹视轴突投射依赖两套信号：ephrinB和EphB，Wnt和Ryk，Fzl。 ephrinB1在顶盖内呈内高外低的梯度，EphB2 和B3在视神经呈腹侧高背侧低梯度Segregation of ocular dominance columns in cat striate contexa. Initially the inputs from the LGN serving the eyes (different colour) are intermingled in layer IV.b. Over the course of fetal and early postnatal development, the inputs from the eyes segregate into ocular dominance columns in layer IV.Modification of ocular dominance stripes after monocular deprivationa. A normal monkeyb. A monkey that had been monocularly