中枢神经系统发育及其可塑性.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,中枢神经系统发育及其可塑性,Development of Central Nervous System,and Its Plasticity,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：,神经上皮脑和脊髓构筑,神经环路发育或构筑：,神经元发生突触形成,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,Introduction,Outline,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 period,Concluding Remarks,From 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,神经板期,神经褶期,(C),神经管期,脊椎动物神经管的形成,:,神经管有两个主要的轴线：背腹轴和前后（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，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 cells,The ventral NT,the notochord,The,dorsal NT,the epidermal ectoderm,The neural tube(NT)formation,neural plate,neural groove,neural fold,neural tube,neural tube,Cranial neuropore,anlage brain,anlage spinal cord,Caudal neuropore,CNS,The neural tube formation,A sample in human embryo-developing in fourth to fifth week.Showing neural fold,，,cranial neuropore,，,somite,，,caudal neuropore,etc.,三个原始脑泡是脑的原基,前脑泡,中脑泡,菱脑泡,（后）,前,N,孔闭合,脑 泡,Brain vesicle,端脑,间脑,后脑,末脑,第三脑室,左、右大脑半球,两个侧脑室,背：四叠体,腹：大脑脚,中脑,脑桥、小脑,延髓,脑泡腔,第四脑室,中：中脑导水管,基本保持三层结构,边缘层白质,套层脊髓灰质,管腔中央管,两侧壁套层神经母细胞和成胶质细胞的迅速增生而增厚,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,腹侧,两基板,背侧,两翼板,顶 板,底 板,胚胎第三个月之前，脊髓与脊,柱等长，其下端达脊柱的尾骨；,胚三个月后，因脊柱增长快于,脊髓，脊柱便渐超越脊髓向尾,端延伸，脊髓位置相对上移；,出生前，脊髓下端与第三腰椎,平齐，仅以终丝与尾骨相连；,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,穿出，脊髓位置上移后，脊髓,颈段以下的脊神经根便斜向尾,侧，至腰、骶、尾段的脊神经,根则在椎管内垂直下行，与终,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。,狭义,的概念仅指出生时解剖结构畸形。,广义,的包括出生时各种解剖结构畸形、功能缺陷及代谢、遗传行为的发育异常。,据,WHO(1966),调查了包括,16,个国家的,25,个医学中心的,421,781,次妊娠，发现严重畸形占,0.46%,，轻度畸形占,1.27%,，总发生率为,1.73%,。,我国,1986-1987,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,29,个省市自治区的,945,所医院,124,万多围产儿进行了监测，发现出生缺陷的总发生率平均为,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,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前后孔未闭引起,占总先天畸形发病率的,17,.,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。,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；,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,The first step in wiring the nervous system together is the generation of neurons.,Neuronal structure develops in three major stages:,1.,Cell proliferation,2.,Cell migration,3.,Cell differentiation,The genesis of neurons,Inducting factors,mesoderm,Neuronal progenitor,Glial progenitor,Neural progenitor,ectoderm,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,Noggin,、,Chordin,和,Follistatin,能阻止外胚层中的,BMP,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,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?,glioblast,Neural tube-MSC,Neural-epithelia,Neuroblast,cell,proliferation,-To grow or multiply by rapidly producing new cells,neural tube,Ventricular zone,Marginal zone,Neuroblast,neural tube,cell,proliferation,-a characteristic of the choreography of cell proliferation,合成,DNA,时,(S,期,),，其核位于靠近外侧膜处，然后核又回到靠官腔的位置进行有丝分裂,(M,期,),，有丝分裂产生的子细胞又移行至外界膜，再合成,DNA,并重复其增殖周期。分裂后子细胞,(daughter cell),命运,(fate),如何决定于很多因素，其中非常重要的因素是基因表达,(gene expression),的差异性,而基因表达的调控取决于,transcription factors,的类型。,Both daughter cells cleaved vertically from the precursor remain in the ventricular zone to 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 remains in the ventricular zone to undergo more division.,This mode predominates later in development,neuronal precursor,cell,proliferation,-The fate of the newly formed daughter cells,Ventricular zone precursor cells repeated this pattern until all of the neurons of the cortex have been generated.The 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 precursor 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.,cell,proliferation,-,How does the cleavage plane during cell division 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,（,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,AS-C,和,Delta,等基因的表达，使邻近的细胞不能成为神经前体细胞,（,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,（,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次分裂后产生不同的神经元,（,A,）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录因子,（,B,）,Hb,和,Kr,缺失或持续表达能影响神经母细胞产生不同,GMC,的能力。虚线显示,GMC,或者死亡，或者变成二生（,Hb,缺失）或头生（,Kr,缺失）,GMC,（,C,）、和这三个神经母细胞每次分裂后产生的,GMC,各不相同，但用同样的转录因子来决定它们的命运。和前两次分裂时都表达,Hb,。只分裂三次。运动：运动神经元；中间：中间神经元；胶质：胶质细胞,（,D,）神经母细胞和,GMC,分裂时也将,Numb,蛋白不对称地分配给两个子细胞。,GMC,只分裂一次，产生两个不同的神经细胞，并通过,Numb,的不对称分布使它们选择不同的命运,Neurogenesis in the adult neocortex,Recent finding show:,Although most of the division action is over well before birth,the adult SGZ and SVZ retains some capacity to generate new neuron.,Behavior/functional activity and environment,Neurogenesis in the adult brain is far too limited to repair CNS damage.,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 processes of the radial glia route to the cortical plate,which forms just under the marginal zone,A migrating cell recorded in tissue culture,A:,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,:,A,B,鼠脑,SVZ,细胞：,肌动蛋白丝染,绿色,微管,红色,-,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；,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。,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.,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 preprogrammed.,The fine structure of axons and dendrites also depends on“environmental”factors in the cortex.,3.1 Differentiation of cortical areas,Niss-stained,position of the major vibrissae on the face,vibrissae region of S1,Barrels in S1,-A somatotopic map of the facial vibrissae on mouse cerebral 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 formation,LM:,Modelchemical synapse),Review,：,definition,classify,structure,EM:,Genesis of,connection,:for example,1.The three phases of pathway formation,Pathway selection path,target selection structure,address selection cell,The three phases depends on:,Direct cell-to-cell contract,contract between cells and extracellular secretions of other cell,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 axon,The growing tip of a neurite is called a growth 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 culture,Fasciculation,Cell adhesion molecules(CAMs),“highway”,2.Axon guidance and guidance cues,Target cell,Extracecular moleculars,Special binding,Seconde messenger,Function changes of microbubules and actin,within growth cone,Controlling growth cone extending,Guidance cues:,chemoattraction and actins concentrate in forepart of a GC,chemorepulsion and actins disappear,in forepart of a GC,Membrane receptors,Chemoattraction and,chemorepulsion,Netrin spurs the axon growth toward the midline,The,receptors,of,Netrin,and,Slit,are be regulated in varying from one side of the midline to,other,Push,pull,Slit chase the axon away the midline,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 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-,transmitter 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 growth 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),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 environments 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 from 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 cord injury.This treatment enabled about 5%of the severed axons to regenerate,Fig A,The elimination of cells and synapse,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 with one another for limited quantities of trophic factors produced by the target neurons.,A cell transfiguration away from adhesion surface,Nucleus rupture,Nucleus concretion and dwindle in size,Nucleus crumble,Cell membrane entad-sunken,Forming apoptosis body,Forming half-moon,Chromatin concentrate edge of nucleus membrane,phagocytosis by phagocyte or macrophage,Biological feature for apoptosis or PCD,M 1 2 3 4 5 6,EM,Apoptosis or PCD,2.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 declines.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.,Activity-dependent synaptic rearrangement,1.Synaptic segregation(,分离,),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.,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 bottom target neuron to fire.,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：,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 contex,Initially the inputs from the LGN serving the eyes(different colour)are intermingled in layer IV.,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 deprivation,A normal monkey,A monkey that had been monocularly deprived for 22 months,starting at 2 weeks of age.The nondeprived eye has been injected,revealing expanded ocular dominance columns in lyer IV.,Torsten Wiesel,The ocular dominance shift,electrophysiological recording from the neuron in striate contex,Elementary mechanisms of cortical