大白鼠大脑视区皮质棘器的微细结构

用电镜对大鼠大脑视区皮质内锥体细胞树突侧棘的棘器作了观察,并分析了其微细结构。棘器是大脑皮质内侧棘结构的一个显著特点,系由被嗜锇性的致密带或颗粒分隔的一些囊或管组成的,它们是复杂多形态的结构。棘器一般位于侧棘小头内,本文也报导了小柄内的棘器。突触后膜和棘器间可见有微丝连接,偶见棘器附近有核糖体。棘器膜性囊或管的形态与滑而内质网相似,说明二者系同源结构。几种形态的棘器中,Gray氏棘器和管形棘器仅见于哺乳动物大脑皮质内,未能在低位中枢神经系统内见到,因而认为棘器可能与脑新皮质的特异性功能有特殊的关系。     

大鼠皮质大颗粒泡的超微结构

用电镜在4只猫听区皮质和3只大白鼠额叶皮质中观察了大颗粒泡的超微结构。在2031个突触面上,共见到大颗粒泡282个。1.大颗粒泡的位置:在104个突触前囊中含有大颗粒泡135个,它们多位于突触前囊的后部(64/135),位于前囊的中部或接近突触前膜者较少。有的大颗粒泡不在突触前囊内,而位于轴突、树突或个别例在树突侧棘中。2.大颗粒泡数目:大脑皮质中的大颗粒泡数目较少。在各种成分中(包括突触前囊、轴突、树突以及其他成分)计见282个大颗粒泡,在一个成分中含1个大颗粒泡的占多数(78.80％)。个别例有含有6个者。多数突触前囊无大颗粒泡。3.大颗粒泡的形态:多为圆形或卵圆形,亚铃形或不整形者也有之。致密核心多数致密,有的并不致密而显得灰淡,有的致密核心呈网状,或在一个包膜内有两个核心。有的膜下环并不明显。4.大颗粒泡的大小不一。本文对大颗粒泡和某些递质的可能关系进行了讨论。     

海马的树突和树－树连接的超微结构

用电镜方法观察了大白鼠ＣＡ１区的神经组织超微结构，发现神经毯内的树突、侧棘、轴突以及神经胶质非常复杂。树突内微管显著。侧棘有不同的形态类型，有些侧棘常有小棘伸出。棘器不仅出现在侧棘内，而且在一些树突内也可遇见。某些侧棘内可见颗粒小泡或包被小泡。神经毯内广泛存在轴－树突触（圆形小泡，Ⅱ型突触），轴－棘突触（圆形小泡，Ⅰ型突触）和树－树突触（圆形小泡，Ⅲ型突触）。此外，还首次在海马内发现非突触性的树－树紧密连接，它可能是假突触，其功能意义有待进一步研究。本文提示海马树突和突触的复杂性可能对学习和记忆有着重要的作用。     

海马的树突和树－树连接的超微结构

用电镜方法观察了大白鼠ＣＡ１区的神经组织超微结构，发现神经毯内的树突、侧棘、轴突以及神经胶质非常复杂。树突内微管显著。侧棘有不同的形态类型，有些侧棘常有小棘伸出。棘器不仅出现在侧棘内，而且在一些树突内也可遇见。某些侧棘内可见颗粒小泡或包被小泡。神经毯内广泛存在轴－树突触（圆形小泡，Ⅱ型突触），轴－棘突触（圆形小泡，Ⅰ型突触）和树－树突触（圆形小泡，Ⅲ型突触）。此外，还首次在海马内发现非突触性的树－树紧密连接，它可能是假突触，其功能意义有待进一步研究。本文提示海马树突和突触的复杂性可能对学习和记忆有着重要的作用。     

小鼠视皮质锥体神经元树突棘和突触的发育

目的:通过观察小鼠视皮质锥体神经元正常发育过程中树突棘的形态变化,研究树突棘与突触的发生及其可塑性的关系.方法:利用DiI散射方法标记小鼠视皮质锥体神经元树突棘,使用共聚焦显微镜对其进行观察分析;同时利用透射电子显微镜技术,对树突棘的超微结构进行分析.结果:树突棘的形态大小及其密度随发育而变化;成熟树突棘内部存在滑面内质网与棘器;树突棘参与了大部分突触后成分的构成.结论:树突棘的发育过程与突触的形成以及突触可塑性密切相关.     

脑内神经元的树突侧棘与棘突触

<正> 神经元由细胞体、轴突和树突组成。从种系进化来看,动物越高等中枢神经元的树突分支越丰富,扩展的范围也越大。从动物个体发育来看,脑内神经元树突及其分支的形态特征在出生后仍继续形成和发展,大脑皮层锥体细胞的树突即是出生后继续生长的例子。树突分支的形态与排列方式及其伸展范围在不同动物及不同神经元之间有差异,使用特殊的组织染色方法(如高尔基银染色法等)和电镜方法可以显示树突表面的刺状或芽状小突起,这就是侧棘(spines),或简称棘,也称侧芽(gemmules)(图1)。中枢神经元的树突侧棘在系统发生和个体发生中代表着神经元演化与成熟的程度,其功能是接受信息和形成突触连接,     

小鼠海马CA1区锥体神经元树突棘的发育

目的 对小鼠海马CA1区锥体神经元正常发育中树突棘密度及各种形态变化进行分析测定,为深入研究突触发生及突触可塑性提供直接的形态学依据.方法 分别取出生后0、5、10、20及30d 5个年龄段的C57BL/6小鼠各10只,采用基因枪对小鼠海马CA1区锥体神经元树突棘进行亲脂性荧光染料DiI标记,通过激光共焦显微镜对其进行观察分析;同时利用透射电镜技术对树突棘的超微结构进行分析.结果 树突棘的形态、大小及其密度随小鼠发育而变化,成熟树突棘内部存在滑面内质网与棘器,可能参与了突触后膜结合蛋白及其转运体的合成.结论 树突棘的发育过程与突触连接的形成以及突触可塑性密切相关.     

家兔脊髓下橄榄投射的突触特点——HRP顺行标记法电镜研究

将HRP注入家兔脊髓腰膨大灰质,在对侧下橄榄背侧副核内显示出大量HRP顺行标记的脊髓纤维终末。并用电子显微镜观察这些标记终末构成的突触。标记终末主要含圆形清亮囊泡,少数含扁形或多形清亮囊泡,清亮囊泡间常夹有散在的大致密芯囊泡。在下橄榄背侧副核内,大部分标记终末形成轴树突触,少数形成轴体突触。有一标记终末同时含圆形及扁形两种清亮囊泡,各与一树突及一胞体构成突触。特别是标记终末还参与构成轴轴突触及突触球。本文还对这些特殊结构的机能意义进行了初步探讨。     

小鼠海马CA1区轴棘突触树突棘头与突触后致密体大小的相关性

目的探讨小鼠海马CA1区兴奋性轴棘突触树突棘头与突触后致密体(postsynaptic density,PSD)是否存在大小的相关性.方法利用Golgi染色、超薄连续切片及NIH图像分析系统测量海马CA1区锥体细胞树突棘头及突触后致密体的大小.结果光镜下测量海马CA1区第2、3级顶树突的树突棘头平均面积为(0.429±0.230)μm2,频数分布为正偏态分布曲线.电镜所测树突棘头的平均体积为(0.032 63±0.024 03)μm3;PSD平均体积为(0.002 318±0.001 362)μm3,PSD与树突棘头体积之比为0.106±0.035.树突棘头体积频数分布曲线和PSD体积频数的分布曲线非常相似,两者呈显著的正相关.结论海马CA1区轴棘突触的树突棘头大小与其突触后致密体的大小具有显著的相关性.     

大脑皮质内树突上突触的超微结构

本文用电镜方法观察大白鼠大脑视区皮质内树突上突触的超微结构。研究结果表明大脑皮质内的突触以轴-树突触和轴-棘突触占优势。轴-树突触按结构有GrayⅠ型和Ⅱ型两种。在视区皮质内有时可见到轴-嵴突触、树-树突触和棘-树突触,它们均属GrayⅠ型(含圆形突触小泡)突触。     

Three-dimensional analysis of dendritic spines. II. Spine apparatus and other cytoplasmic components

A total of 342 dendritic spines (193 from the visual and 149 from the cerebellar cortex of the mouse) were analyzed in serial and several hundred of thousands of them in single sections, with respect to the presence and organization of the spine apparatus and other cytoplasmic components. The continuity of the spine apparatus with the smooth endoplasmic reticulum of the dendritic trunk was shown in three-dimensional reconstructions. The dense material of the spine apparatus was divided into "inner dense plate" and "outer dense plate". The close relationship between the outer dense plate and the postsynaptic density suggests that the spine apparatus functions as a postsynaptic protein synthesizing centre. The material from the outer dense plate could be used for a dynamic extension of the synaptic active zone. An extraspinous spine apparatus of the axon initial segment was partially reconstructed. Polyribosomes were found in all large spines of the visual cortex but were not so frequent in small spines and in Purkinje cell dendritic spines. Microfilamentous network and intermediate filaments occurred in the spines. The smooth endoplasmic reticulum of Purkinje cell dendritic spines was reconstructed. No spine apparatus and dense material were present in these spines.     

Morphological changes of dendrites in the human edematous cerebral cortex. A transmission electron microscopic study

The structural pathology of dendritic processes has been examined in 38 patients with clinical diagnosis of brain trauma, brain tumours and congenital malformations. Cortical biopsies of frontal, parietal, temporal and occipital cortex were conventionally processed for transmission electron microscopy. Isolated ultrathin sections and montages of electron micrographs were used to trace the intracortical dendritic course. Swollen and beaded dendrites were observed in all cases examined, which exhibited fragmentation of limiting plasma membrane and cytoskeletal structures. The swollen dendrites showed vacuolization, dense residual bodies, enlarged rough and smooth endoplasmic reticulum, edematous clear and dark mitochondria, a decreased synaptic density of shaft synapses, edematous and dystrophic changes of spine apparatus and a partial loss of dendritic spines. A wide variety of dendritic spine shapes were observed: mushroom-type, stubby, gem-like filiform spine, and megaspine, considered as spine dysgenesis in the congenital malformations and spine pathology and spine plasticity in brain traumatic injuries and brain tumours. The multifactorial processes associated with brain edema and brain ischemia, such as calcium overload, activation of calcium-dependent proteolytic enzymes, protein aggregation, glutamate-induced neurotoxicity, release of lysosomal enzymes, deficit of ATP, stress oxidative and lipid peroxidation have been considered in relation with the pathological dendritic changes. Dendrotoxicity due to brain edema and brain ischemia seems to be the fundamental pathogenetic mechanism.     

Stellate neurons in rat dorsal cochlear nucleus studies with combined Golgi impregnation and electron microscopy: synaptic connections and mutual coupling by gap junctions

Summary Stellate neurons in the outer two layers of the rat dorsal cochlear nucleus (DCN) were studied by the Golgi-EM method. Stellate cell bodies are usually spherical or ovoidal and range from 9 m to 14 m in mean diameter. The smallest cells are situated underneath the ependymal layer and the largest cells in layer 2. Primary dendrites are short, thin and smooth and arise abruptly from the perikaryon, without a tapering main stem. Meandering secondary and tertiary dendrites extend in all directions, carry few pleomorphic spines lacking a spine apparatus and often show artifactual beading. The axons are impregnated only for a short distance (10–45 m). The nucleus is indented, the nucleolus varies in position, and the chromatin, evenly dispersed in the centre, forms small clumps along the nuclear envelope. The cytoplasm is rich in free polyribosomes and contains scattered cisterns of granular endoplasmic reticulum. Varicosities of thin fibres, containing round synaptic vesicles, form asymmetric synapses on perikarya, dendritic shafts and spines of stellate cells. Such fibres run parallel to the long axis of the DCN or are oriented radially and are interpreted as axons of cochlear granule cells. Two kinds of bouton containing pleomorphic vesicles, one kind electron lucent and the other electron dense, form symmetric synapses on perikarya and dendritic shafts of stellate cells. The lucent boutons occur more frequently than the dense boutons, especially on the distal dendritic branches. The boutons with pleomorphic vesicles presumably represent terminals of local circuit neurons, probably the stellate and cartwheel cells.In addition, stellate cells show numerous dendro-somatic and dendro-dendritic appositions characterized by gap junctions and puncta adhaerentia. Most of the dendrites involved in these appositions resemble stellate cell dendrites and it is concluded that DCN stellate cells are coupled electrotonically with one another. The axons of stellate cells acquire a thin myelin sheath. Since the Golgi impregnation did not stain axons of stellate cells past this point, we were unable to demonstrate the synaptic targets of stellate cells.     

国人胎儿小脑皮质Purkinje细胞层突触的发育

应用超薄切片观察了人胚 19、2 1、2 6、和 34周小脑皮质 Purkinje细胞层突触的发育。观察到轴—树、轴—棘—棘、轴—树—树、树—树、体—体、棘—体突触与树—树—树连续性突触及树—轴—树嵴状突触超微结构的发育。突触多为 Gray 型 ,而 型较少     

Fine structural changes in the endolymphatic sac induced by calcium loading in the tree frog, Hyla arborea japonica

The growth rate of calcium carbonate (CaCO3) crystals in the endolymphatic sac was modulated, and morphological changes in this organ were observed by light and electron microscopy. When calcium chloride (CaCl2) was given to the three frog for a short period (3 days to 2 weeks), CaCO3 crystal production was accelerated. Epithelial cells enlarged, their rough endoplasmic reticulum (rER) and Golgi apparatus developed, and dense material increased around CaCO3 crystals and/or in the endolymphatic lumen. In addition, multiluminal endolymphatic chambers appeared in some frogs. On the other hand, as the CaCl2 loading period lengthened and CaCO3 crystal formation decreased or stopped, the epithelial cells became flat and extended with scanty cytoplasm, and the rER and Golgi apparatus decreased in number and size. Furthermore, the amount of dense material around CaCO3 crystals and in the lumen decreased. These findings suggest that the rER, Golgi apparatus and dense material have key roles in the production of CaCO3 crystals.     

Relationships between synaptic junctions, puncta adhaerentia and the spine apparatus at neocortical axo-spinous synapses

Summary A total of 80 cotical axo-spinous synaptic junctions were reconstructed from serial sections and about 100,000 were analyzed in single sections. Special attention was paid to the occurrence of puncta adhaerentia associated with perforated, annulate or horseshoe-shaped (=complex) synaptic junctions and to the presence and proximity of the spine apparatus. Further evidence is presented that the spine apparatus has no relationship to simple (round or oval) synaptic specializations, but is present in association with at least 91% of complex junctions. The spine apparatus points towards the punctum adhaerens which in at least 71% of cases seems to be an integral part of the complex synapse. Direct continuity was found between the dense material of the spine apparatus and the punctum adhaerens. It is suggested, in accordance with other recent studies, that expansion of the synaptic active zone occurs by the addition and transformation of puncta adhaerentia. The spine apparatus may participate in this dynamic process as a possible donor of specific postsynaptic proteins.     

Synaptic plasticity in the oedematous human cerebral cortex

Synaptic plastic changes are fundamental events which occur spontaneously during development, maturity and aging processes or can be induced by injury or trauma. To examine lesion-induced synaptic plasticity, cortical biopsies were taken from the frontal, parietal, temporal and occipital cortex of living patients during neurosurgical treatment of brain trauma, brain tumours and vascular malformations, and processed for transmission electron microscopy. Enlargement of both pre- and postsynaptic endings, irregularly shaped, lobulated, stellate and bifurcated presynaptic endings and conformational changes of dendritic spines were observed. Numerous flat, curved and invaginated axodendritic and axospinous asymmetric synapses were distinguished and a smaller proportion of axodendritic and axosomatic symmetric synapses. Activated or sensitized synapses showed numerous frontline spheroid synaptic vesicles, prominent dense presynaptic dense projections and increased length of synaptic membrane complex. Perforated synapses, multiple synapses and serial synapses were also found evincing synaptic splitting and formation of new synaptic connections. The overall images suggest increased number of excitatory circuits, which were correlated with the tonico-clonic convulsion or post-traumatic seizures observed in some patients. Numerous coated vesicles were observed in pre- and postsynaptic structures. Increased number of polyribosomes were found in the dendritic shafts. The dilated spine apparatus, the coated vesicles and the increased number of polyribosomes seem to represent a system for synthesis, transport and storage of synaptic proteins for the formation of new synapses. Coexisting synaptic plasticity and synaptic degeneration were observed in the patients under study. Dendritic and astrocyte synapse-like junctions were also characterized.     

Computational study of an excitable dendritic spine

1. A compartmental model was employed to investigate the electrical behavior of a dendritic spine having excitable membrane at the spine head. Here we used the Hodgkin and Huxley equations to generate excitable membrane properties; in some cases the kinetics were modified to get a longer duration action potential. Passive membrane was assumed for both the spine stem and the dendritic shaft. Synaptic input was modeled as a transient conductance increase (alpha-function) that lies in series with a battery (that corresponds to an excitatory or inhibitory synaptic equilibrium potential). 2. Threshold conditions for an action potential at the spine head membrane were found to be sensitive to the membrane properties at the spine head and to the conductance loading provided by the spine stem and the dendritic tree. Increasing either the number or the open times of the excitable channels had the effect of lowering spike threshold voltage. Increasing the spine stem resistance (RSS) or increasing the input resistance at the spinal base (RSB) also lowered the spike threshold voltage. Because a preexisting dendritic depolarization reduced the spine stem current, this lowered the spike threshold voltage, and this threshold was also shown to be sensitive to the distribution of membrane potential along the dendrite. 3. For each set of spine and dendritic parameters, there was an optimal range of RSS values for which the excitable properties at the spine head membrane resulted in maximal amplification of the dendritic excitatory postsynaptic potential (EPSP), when compared with that produced by a corresponding passive spine. This optimal range depended (with nonlinear sensitivity) on the properties of the voltage-gated channels at the spine head membrane. The maximal amplification found (for each of several sets of parameters) ranged from two to thirteen times. 4. Near this optimal range of RSS values, there was maximal (nonlinear) sensitivity of the dendritic EPSP amplitude to small changes in RSS. A minor decrease resulted in a subthreshold response at the spine head, and this resulted in a large decrease in the EPSP amplitude at the spine base. Increasing the value of RSS above this optimal range decreased the amount of spine stem current flowing to the spine base (by Ohm's law); this decreased the EPSP amplitude at the spine base. The demonstration of this optimum agrees with earlier expectations and results. 5. Excitable dendritic spines can be seen to provide an anatomical arrangement that economizes both excitable and synaptic channels. A small number of these channels (located in spine head membrane) can produce a large dendritic depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)