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。     

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。     

延髓后角脑啡肽超微结构定位和非突触部位释放——脑啡肽突触前抑制痛觉传递的形态学基础

阿片肽在后角镇痛的作用机理,被认为是通过突触前抑制一级传入纤维P物质释放的结果,然而始终未获得形态学的证实。鉴于一级传入纤维存在大量阿片受体的事实,曾提出阿片肽突触前抑制可能是通过非突触的轴-轴作用。为了验证这一设想,本文用免疫组化方法,详细观察了大鼠延髓后角浅层亮氨酸脑啡肽(L-ENK)轴突终末的突触结构和胞吐释放。电镜观察显示,延髓后角ENK终末可分为两类,第一类终末除了含圆形小清亮囊泡外,还有较多的大颗粒小泡(一般7个以上),主要分布于Ⅰ层,很少看到此类终末形成突触;第二类终末,一般含较多圆形清亮小泡和少量大颗粒小泡(一般不超过3个),它们分布于Ⅰ层和Ⅱ层,此类终末主要形成轴-树突触和少量的轴-体突触。只见到一例轴-轴突触,其突触后成分为未标记的R型终末,此外还见到ENK阳性树突成为中央终末的突触后成分。在去传入神经条件下,上述各类终末皆可见到ENK阳性大颗粒小泡的胞吐形成,它们皆位于非突触区,而在突触部位可见到清亮小泡胞吐像,上述结果提示后角ENK非突触部位释放可能是哭触后抑制一级传入纤维P物质释放的形态学基础。     

SP,CGRP,ENK样阳性纤维终末在猫骶髓后连合核内的分布特征及超微结构

本实验用免疫组化电镜技术对骶髓后连合核中SP祥、CGRP样、L-ENK样阳性终末进行了观察,结果表明:SP样阳性终末主要含圆形清亮小泡,间有少量颗粒囊泡,主要与中、小树突形成不对称型轴-树突触(93%);还可见到不对称型轴-体突触(5%);也可见到少量的轴-轴突触(2%),SP样阳性终末为突触后成分。CGRP样阳性终末以含圆形清亮小泡为主,有的终末内混有颗粒囊泡。大多数终末(89%)与树突构成轴-树突触,但以远侧树突为主;也有少数(6%)的CGRP样阳性终末与胞体形成轴-体突触;还观察到由阴性终末与CGRP样阳性终末构成的轴-轴突触。L-ENK样阳性终末以含圆形清亮小泡为主,有时可见散在的颗粒囊泡,多与中、小树突形成不对型轴-树突触(92%);也观察到轴-体突触(5%)和轴-轴突触(3%)。     

猫孤束核胶状质亚核的突触构筑学研究

用透射电镜对猫的孤束核胶状质亚核(SNG)的突触型式进行了观察,除看到已报导的轴—树突触、轴—体突触、树—树突触外,还发现该核内含有轴—轴突触及突触球等结构。SNG内轴—树突触最常见,而轴—体突触、轴—轴突触和树—树突触则较少。各类突触中的突触囊泡多为圆形清亮囊泡,而扁平清亮囊泡和大颗粒囊泡较少。扁平清亮囊泡多与圆形清亮囊泡共存于同一轴—轴突触终末内。轴—轴突触均为对称型突触,有时与树突或胞体相连形成轴—轴—树突触或轴—轴—体突触。突触球多为以树突和棘为中心的中心树突型突触球。此外在SNG内还观察到嵴突触,并联突触等连接形式。SNG内突触的复杂性表明传入冲动在该核中可能经过扩散、汇聚和突触前抑制等多种复杂的整合过程调节内脏活动。     

脊髓侧角区5-HT、TH、SP和L-ENK免疫反应纤维和终末的超微结构

本文应用免疫细胞化学ABC法,在电镜下观察脊髓侧角区单胺能和某些肽能纤维及末梢的突触组合。大鼠侧角内的5-HT、TH、SP和L-ENK免疫反应纤维均为无髓纤维。在侧角细胞簇内,这些纤维穿行于胞体之间,有的与胞体相邻,但很少与胞体形成轴-体突触。这些单胺和肽类纤维也与树突伴行,在树突束内数量最多。有时一小束无髓纤维都含同一种免疫反应物质。轴-树突触是各种免疫反应纤维终末所形成突触的主要形式。各种纤维终末所含的小泡多为圆清亮小泡,或兼有少数大颗粒泡。SP和L-ENK纤维膨体内的小泡与其终末内者不同,大颗粒泡较多,有时约占半数。各种免疫反应终末所组成参与的突触,对称或非对称型均不显现优势。     

大鼠三叉神经脊束核尾侧亚核胶状质非小球突触成分

用透射电镜观察了大鼠三叉神经脊束核尾侧亚核胶状质神经毡非小球的突触成分。非小球的突触大部分为轴树突触,此外还见到轴轴、树树及树轴突触。它们的轴突终末成分,按所含小泡的形状,区分为圆形小泡终末、扁平小泡终末、多形小泡终末及大颗粒小泡终末。圆形小泡终末根据小泡的大小又有大圆形小泡终末及小圆形小泡终末。本文还讨论了突触分类及各种轴突终末的机能意义。     

大鼠三叉神经脊束核尾侧亚核胶状质突触小球的超微结构

用透射电镜观察了大鼠三叉神经脊束核尾侧亚核胶状质突触小球的各种突起成分及突触联系。突触小球的中央轴突终未与周围两类 (一、二型)树突棘,树突干形成非对称的轴树突触。含突触小泡的二型树突棘、树突干与不含小泡的一型树突棘、树突干形成对称的树树突触,并与中央轴突终末形成树轴突触。周围轴突终末(P)与中央轴突终末形成对称的轴轴突触,并与小球内的树突形成对称的轴树突触。     

家兔脊髓腰骶部中间外侧核区的超微结构——神经纤维网和突触

本实验用家兔7只,取腰髓2～4和骶髓2～4节中间外侧核区,做超薄切片,电镜观察。此区的神经纤维网内含树突、轴突、轴突终末、终端树突、突触和突触球。胶质细胞的突起穿行其间。树突散在,形态和大小多变。轴突则常成束分布。突触连接以轴树和轴体突轴为多见,偶见轴轴突触。多数突触单独存在,部分形成以树突或轴突为中心的突触球。突触内的突触小泡有清亮的圆形、椭圆形、扁平形和不规则形,还有相当多见的大致密核心小泡和少数有衣小泡。依终末囊内突触小泡的形态和突触前后膜的对称与不对称,所见突触可分为三类:1.圆形小泡不对称型;2.扁平小泡对称型;3.其它中间类型。     

Presynaptic plasticity at two giant auditory synapses in normal and deaf mice

Large calyceal synapses are often regarded as simple relay points, built for high-fidelity and high-frequency synaptic transmission and a minimal requirement for synaptic plasticity, but this view is oversimplified. Calyceal synapses can exhibit surprising activity-dependent developmental plasticity. Here we compare basal synaptic transmission and activity-dependent plasticity at two stereotypical calyceal synapses in the auditory pathway, the endbulb and the calyx of Held. Basal synaptic transmission was more powerful at the calyx than the endbulb synapse: the amplitude of evoked AMPA receptor-mediated excitatory postsynaptic currents (eEPSCs) was significantly greater at the calyx, as were the release probability, and the number of release sites. The quantal amplitude was smaller at the calyx, consistent with the smaller amplitude of spontaneous miniature EPSCs at this synapse. High-frequency trains of stimuli revealed that the calyx had a larger readily releasable pool of vesicles (RRP), less tetanic depression and less asynchronous transmitter release. Activity-dependent synaptic plasticity was assessed in congenitally deaf mutant mice ( dn/dn ). Previously we showed that a lack of synaptic activity in deaf mice increases synaptic strength at the endbulb of Held via presynaptic mechanisms. In contrast, we have now found that deafness does not affect synaptic transmission at the calyx synapse, as eEPSC and mEPSC amplitude, release probability, number of release sites, size of RRP, tetanic depression and asynchronous release were unchanged compared to normal mice. Synaptic transmission at the calyx synapse is more powerful and has less capacity for developmental plasticity compared to the endbulb synapse.     

Timing and efficacy of transmitter release at mossy fiber synapses in the hippocampal network

It is widely accepted that the hippocampus plays a major role in learning and memory. The mossy fiber synapse between granule cells in the dentate gyrus and pyramidal neurons in the CA3 region is a key component of the hippocampal trisynaptic circuit. Recent work, partially based on direct presynaptic patch-clamp recordings from hippocampal mossy fiber boutons, sheds light on the mechanisms of synaptic transmission and plasticity at mossy fiber synapses. A high Na⁺ channel density in mossy fiber boutons leads to a large amplitude of the presynaptic action potential. Together with the fast gating of presynaptic Ca²⁺ channels, this generates a large and brief presynaptic Ca²⁺ influx, which can trigger transmitter release with high efficiency and temporal precision. The large number of release sites, the large size of the releasable pool of vesicles, and the huge extent of presynaptic plasticity confer unique strength to this synapse, suggesting a large impact onto the CA3 pyramidal cell network under specific behavioral conditions. The characteristic properties of the hippocampal mossy fiber synapse may be important for pattern separation and information storage in the dentate gyrus-CA3 cell network.     

Estradiol increases spine density and NMDA-dependent Ca2+ transients in spines of CA1 pyramidal neurons from hippocampal slices

To investigate the physiological consequences of the increase in spine density induced by estradiol in pyramidal neurons of the hippocampus, we performed simultaneous whole cell recordings and Ca2+ imaging in CA1 neuron spines and dendrites in hippocampal slices. Four- to eight-days in vitro slice cultures were exposed to 17beta-estradiol (EST) for an additional 4- to 8-day period, and spine density was assessed by confocal microscopy of DiI-labeled CA1 pyramidal neurons. Spine density was doubled in both apical and basal dendrites of the CA1 region in EST-treated slices; consistently, a reduction in cell input resistance was observed in EST-treated CA1 neurons. Double immunofluorescence staining of presynaptic (synaptophysin) and postsynaptic (alpha-subunit of CaMKII) proteins showed an increase in synaptic density after EST treatment. The slopes of the input/output curves of both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) postsynaptic currents were steeper in EST-treated CA1 neurons, consistent with the observed increase in synapse density. To characterize NMDA-dependent synaptic currents and dendritic Ca2+ transients during Schaffer collaterals stimulation, neurons were maintained at +40 mV in the presence of nimodipine, picrotoxin, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). No differences in resting spine or dendritic Ca2+ levels were observed between control and EST-treated CA1 neurons. Intracellular Ca2+ transients during afferent stimulation exhibited a faster slope and reached higher levels in spines than in adjacent dendrites. Peak Ca2+ levels were larger in both spines and dendrites of EST-treated CA1 neurons. Ca2+ gradients between spine heads and dendrites during afferent stimulation were also larger in EST-treated neurons. Both spine and dendritic Ca2+ transients during afferent stimulation were reversibly blocked by D, L-2-amino-5-phosphonovaleric acid (D,L-APV). The increase in spine density and the enhanced NMDA-dependent Ca2+ signals in spines and dendrites induced by EST may underlie a threshold reduction for induction of NMDA-dependent synaptic plasticity in the hippocampus.     

Light and electron microscopic observations on the inner plexiform layer of the rabbit retina

By comparison of electron micrographs with light microscopical specimens impregnated with the Golgi technique, the large endings of the rod bipolar cells have been identified in the innermost region of the inner plexiform layer of the rabbit retina. The rod bipolar endings contain ribbons and synaptic vesicles, do not synapse with the perikaryon of the ganglion cells, are presynaptic to ganglion cell dendrites and to nerve processes which contain synaptic vesicles but lack ribbons. In these synaptic contacts a ribbon is closely associated with the presynaptic membrane and a dense web of fuzzy material is adherent to the cytoplasmic aspect of the postsynaptic membrane. Commonly, one of these synaptic contacts involves a rod bipolar ending and two postsynaptic processes. The postsynaptic process which is provided with synaptic vesicles is often, in turn, presynaptic to the same rod bipolar ending. This synaptic contact is characterized by the presence of a cluster of vesicles closely related to the presynaptic membrane, whereas the postsynaptic membrane lacks a definite subsynaptic web. In the intermediate and scleral regions of the inner plexiform layer endings containing ribbons and synaptic vesicles show with neighboring nerve processes a synaptic pattern similar to the rod bipolar endings. Nerve processes containing synaptic vesicles but lacking ribbons are presynaptic to the perikaryon and dendrites of the ganglion cells; the synaptic contact shows a cluster of vesicles adherent to the presynaptic membrane. Bipolar cells are proposed as the source of the ribbon containing processes while amacrine cells are proposed as the source of the processes devoid of ribbons and presynaptic to both bipolar endings and ganglion cell dendrites and perikarya.     

血管性痴呆大鼠海马synapsinⅠ及其磷酸化水平的动态变化

目的：观察血管性痴呆大鼠海马区突触结构和突触蛋白synapsin I及其磷酸化水平的变化，探讨血管性痴呆大鼠突触传递障碍的可能机制。方法: 采用双侧颈总动脉夹闭再灌注同时腹腔注射硝普纳建立血管性痴呆模型，在15 d、1月、2月和4月等时点，电镜观察大鼠海马CA1区突触结构的病理改变，应用免疫组织化学染色法测定血管性痴呆大鼠海马synapsinⅠ及其磷酸化水平的变化。结果: 假手术组大鼠海马CA1区未见明显病理改变，突触前小泡聚集成簇，模型组突触前后膜界限不清，突触后致密物减少，突触前囊泡分布分散、聚集囊泡簇减少，并随造模时间的延长，病理改变加重；模型组大鼠海马CA1区synapsin I阳性产物表达明显减少(P<0.01)，DG区分子层无明显变化(P>0.05)；模型组大鼠海马磷酸化synapsin I（p-synapsin I）阳性细胞明显减少(P<0.01,P<0.05)，15 d和1月时点大鼠海马DG区和CA1区p-synapsin I阳性细胞表达较假手术组增强(P<0.01)，2月和4月时点CA1区p-synapsin I阳性细胞表达较假手术组减弱(P<0.01)，而DG区无明显变化(P>0.05)。结论: VD模型大鼠海马突触结构受损，突触小泡簇减少；synapsinⅠ及其磷酸化水平表达降低，突触传递前机制受损可能是VD突触传递障碍的机制之一。     

Age-related synapse loss in hippocampal CA3 is not reversed by caloric restriction

Caloric restriction (CR) is a reduction of total caloric intake without a decrease in micronutrients or a disproportionate reduction of any one dietary component. While CR attenuates age-related cognitive deficits in tasks of hippocampal-dependent memory, the cellular mechanisms by which CR improves this cognitive decline are poorly understood. Previously, we have reported age-related decreases in key synaptic proteins in the CA3 region of the hippocampus that are stabilized by lifelong CR. In the present study, we examined possible age-related changes in the functional microcircuitry of the synapses in the stratum lacunosum-moleculare (SL-M) of the CA3 region of the hippocampus, and whether lifelong CR might prevent these age-related alterations. We used serial electron microscopy to reconstruct and classify SL-M synapses and their postsynaptic spines. We analyzed synapse number and size as well as spine surface area and volume in young (10 months) and old (29 months) ad libitum fed rats and in old rats that were calorically restricted from 4 months of age. We limited our analysis to SL-M because previous work demonstrated age-related decreases in synaptophysin confined to this specific layer and region of the hippocampus. The results revealed an age-related decrease in macular axo-spinous synapses that was not reversed by CR that occurred in the absence of changes in the size of synapses or spines. Thus, the benefits of CR for CA3 function and synaptic plasticity may involve other biological effects including the stabilization of synaptic proteins levels in the face of age-related synapse loss.     

Dense core vesicles resemble active-zone transport vesicles and are diminished following synaptogenesis in mature hippocampal slices

Large dense core vesicles (approximately 100 nm) contain neuroactive peptides and other co-transmitters. Smaller dense core vesicles (approximately 80 nm) are known to contain components of the presynaptic active zone and thought to transport and deliver these components during developmental synaptogenesis. It is not known whether excitatory axons in area CA1 contain such dense core vesicles, and whether they contribute to synaptic plasticity of mature hippocampus. Serial section electron microscopy was used to identify dense core vesicles in presynaptic axons in s. radiatum of area CA1 in adult rat hippocampus. Comparisons were made among perfusion-fixed hippocampus and hippocampal slices that undergo synaptogenesis during recovery in vitro. Dense core vesicles occurred in 26.1+/-3.6% of axonal boutons in perfusion fixed hippocampus, and in only 17.6+/-4.5% of axonal boutons in hippocampal slices (P<0.01). Most of the dense core vesicle positive boutons contained only one dense core vesicle, and no reconstructed axonal bouton had more than a total of 10 dense core vesicles in either condition. Overall the dense core vesicles had average diameters of 79+/-11 nm. These small dense core vesicles were usually located near nonsynaptic membranes and rarely occurred near the edge of a presynaptic active zone. Their size, low frequency, locations, and decrease following recuperative synaptogenesis in slices are novel findings that merit further study with respect to small dense core vesicle content and possible contributions to synapse assembly and plasticity in the mature hippocampus.     

Retrograde modulation of presynaptic release probability through signaling mediated by PSD-95-neuroligin

The structure and function of presynaptic and postsynaptic components of the synapse are highly coordinated. How such coordination is achieved and the molecules involved in this process have not been clarified. Several lines of evidence suggest that presynaptic functionalities are regulated by retrograde mechanisms from the postsynaptic side. We therefore sought postsynaptic mechanisms responsible for trans-synaptic regulation of presynaptic function at excitatory synapses in rat hippocampal CA1 pyramidal neurons. We show here that the postsynaptic complex of scaffolding protein PSD-95 and neuroligin can modulate the release probability of transmitter vesicles at synapse in a retrograde way, resulting in altered presynaptic short-term plasticity. Presynaptic beta-neurexin serves as a likely presynaptic mediator of this effect. Our results indicate that trans-synaptic protein-protein interactions can link postsynaptic and presynaptic function.     

APP/PS1转基因AD鼠海马CA1区神经元突触超微结构

目的:探讨携带5个家族性基因突变的APP/PS1转基因阿尔茨海默病(AD)(5×FAD)模型小鼠海马CA1区神经元突触超微结构改变。方法:应用透射电镜观察和形态计量学分析5×FAD转基因AD鼠海马CA1区GrayⅠ型突触界面结构参数,包括突触间隙长度、突触间隙面积、突触后致密物浓度和突触界面曲率的变化。结果:5×FAD转基因AD鼠海马CA1区神经元突触活性区长度显著小于对照组,差异有统计学意义;突触后致密物厚度、突触界面曲率及宽度与对照组差异无统计学意义。结论:5个家族性突变基因导致小鼠海马CA1区神经元突触可塑性的改变,这可能是该突变基因导致的发病机制之一。