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。     

关于海马内突触小球超微结构的辨认

用电镜技术对大白鼠海马ＣＡｌ区的突触小球超微结构作了观察，发现有二种形态的突触小球。一种是小球的突触神经成分均封闭在球内，另一种是小球内的苔状纤维终末与球外神经毯内的树突于形成轴－树突触。小球的中央轴突终末即是苔状纤维终末，它不仅与树突侧棘形成轴－棘突触，而且与树突形成轴－树突触。树－树突触在小球内亦可见到。本文就突触小球的结构成分和突触小球的概念等问题进行了讨论。     

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。     

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。     

大鼠下丘脑弓状核突触的衰老性变化

用透射电镜结合体视学方法，对３月龄、１０月龄和３０～３４月龄大鼠弓状核突触进行了定性和定量研究。结果显示：老龄组大鼠神经毯呈萎缩变性相，大树突内脂褐素增多，小到中等大小的树突出现空泡变性、多泡体和膜被多层体等，棘萎缩减少；轴突终末内突触囊泡减少而大颗粒囊泡积聚，部分突触前、后膜变薄、缩短或间断，突触小球少见；轴－体、轴－树和轴－棘突触数减少，突触密度、突触连接带面密度和突触膜总长度降低，ＧｒａｙⅠ型和即Ⅱ型突触间隙增宽。上述结果表明，老年弓状核突触在数量、形态和结构上发生了衰老性改变，这是导致下丘脑神经内分泌衰老障碍的主要原因之一。     

大白鼠海马神经毯内神经胶质突起与神经元突起间关系的超微结构…

用电镜技术观察了大白鼠海马神经毯内的神经胶质突起与神经元突起的超微结构。本文论述了星状胶质细胞突起与神经元的树突、树突侧棘和轴突膜间联系的超微形态特点，发现星状胶质细胞突起广泛分布于神经毯内，与神经元突起间形成膜的紧密并列关系，但不形成突触，也未见二膜间并列处有膜的增厚和突触小泡聚集的现象。星状胶质细胞突起上的棘状突起的超微结构特征不同于树突的侧棘，无棘器的构造。产次发现有的神经胶质棘状突起上有小     

大白鼠海马神经毯内神经胶质突起与神经无突起间关系的超微结构研究

用电镜技术观察了大白鼠海马神经毯内的神经胶质突起与神经元突起的超微结构。本文论述了星状胶质细胞突起与神经元的树突、树突侧棘和轴突膜间联系的超微形态特点，发现星状胶质细胞突起广泛分布于神经毯内，与神经元突起间形成膜的紧密并列关系，但不形成突触，也未见二膜间并列处有膜的增厚和突触小泡聚集的现象。星状胶质细胞突起上的棘状突起的超微结构特征不同于树突的侧棘，无棘器的构造。首次发现有的神经胶质棘状突起上有小棘结构。有些棘状突起借粘着斑与树突形成细胞间连接。     

大鼠海马结构在空间辨别性学习记忆时的突触形态学观察

目的：探讨学习记忆活动是否可以引起大鼠海马结构发生突触可塑变化。方法：电子显微镜下对模型大鼠和对照大鼠的海马结构内突触复合体的形态进行了对比观察。结果：(1)模型大鼠海马CJ43区多形层内多为神经纤维，其中无髓纤维占多数，有髓纤维很少。在无髓纤维间见到形状不规则的轴突终末与周围的树突和树突棘分别形成轴—树突触和轴棘突触，后者多见。突触前膨大内充满圆形清亮、无核心的突触小泡和线粒体。突触后成分多为树突棘并在多处与突触前膜形成活性区，树突棘内见到棘器。(2)对照大鼠海马CA3区多形层内含有大量无髓纤维并见到较少的轴—树突触。该突触形状规则且活性带面积较小，突触后成分多为一个，突触小泡清亮、圆形无核心，偶见线粒体。(3)经Timm染色的两组大鼠海马CA3区多形层的超微结构特点是银颗粒仅沉积在苔藓纤维的髓鞘内和苔藓纤维的大终扣内，线粒体、树突干和树突棘内均无银颗粒。结论：正常生理活动和空间辨别性学习记忆活动均可引致大鼠海马CA3区多形层突触可塑性变化，但两者在形态上有所不同。     

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。     

家兔下橄榄背侧副核的超微结构特点——电镜研究

本实验对7只家兔的下橄揽背侧副核进行了电镜观察。除发现已报道过的轴树突触、轴体突触及以树突为中心的突触球外,还见此核内有轴轴突触、轴突与胞体棘形成的突触,以轴突为中心的突触球及核内微纤维束。轴树突触最常见,突触后成分为树突或棘。轴体突触较少见。有一轴突终末与一胞体棘形成突触,同时还与一树突形成突触。轴轴突触前、后成分中均含圆形囊泡,有时形成轴-轴-树突触串。家兔下橄榄背侧副核内见有两种突触球,一种以树突为中心,另一种以轴突为中心。还发现两个轴突终末同时与另一轴突终末形成轴→轴→轴突触。下橄榄背侧副核内的复杂突触形式,说明传入冲动在其中可能经过扩散、会聚、突触前抑制及整合等复杂的过程。     

Synaptic modifications at the CA3–CA1 synapse after chronic AMPA receptor blockade in rat hippocampal slices

Maintenance of dendritic spines, the postsynaptic elements of most glutamatergic synapses in the central nervous system, requires continued activation of AMPA receptors. In organotypic hippocampal slice cultures, chronic blockade of AMPA receptors for 14 days induces a substantial loss of dendritic spines on CA1 pyramidal neurons. Here, using serial section electron microscopy, we show that loss of dendritic spines is paralleled by a significant reduction in synapse density. In contrast, we observed an increased number of asymmetric synapses onto the dendritic shaft, suggesting that spine retraction does not inevitably lead to synapse elimination. Functional analysis of the remaining synapses revealed that hippocampal circuitry compensates for the anatomical loss of synapses by increasing synaptic efficacy. Moreover, we found that the observed morphological and functional changes were associated with altered bidirectional synaptic plasticity. We conclude that continued activation of AMPA receptors is necessary for maintaining structure and function of central glutamatergic synapses.     

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.     

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.     

Mechanism of the distance-dependent scaling of Schaffer collateral synapses in rat CA1 pyramidal neurons

Schaffer collateral axons form excitatory synapses that are distributed across much of the dendritic arborization of hippocampal CA1 pyramidal neurons. Remarkably, AMPA-receptor-mediated miniature EPSP amplitudes at the soma are relatively independent of synapse location, despite widely different degrees of dendritic filtering. A progressive increase with distance in synaptic conductance is thought to produce this amplitude normalization. In this study we examined the mechanism(s) responsible for spatial scaling by making whole-cell recordings from the apical dendrites of CA1 pyramidal neurons. We found no evidence to suggest that there is any location dependence to the range of cleft glutamate concentrations found at Schaffer collateral synapses. Furthermore, we observed that release probability ( P _r), paired-pulse facilitation and the size of the readily releasable vesicular pool are not dependent on synapse location. Thus, there do not appear to be any changes in the fundamental presynaptic properties of Schaffer collateral synapses that could account for distance-dependent scaling. On the other hand, two-photon uncaging of 4-methoxy-7-nitroindolinyl-caged l -glutamate onto isolated dendritic spines shows that the number of postsynaptic AMPA receptors per spine increases with distance from the soma. We conclude, therefore, that the main synaptic mechanism involved in the production of distance-dependent scaling of Schaffer collateral synapses is an elevated postsynaptic AMPA receptor density.     

A light and electron microscopic study of betaine/GABA transporter distribution in the monkey cerebral neocortex and hippocampus

The present study aimed to elucidate the distribution of betaine/gamma-aminobutyric acid (GABA) transporter-1 (BGT-1) in the normal monkey cerebral neocortex and hippocampus by immunoperoxidase and Immunogold labelling. BGT-1 was observed in pyramidal neurons in the cerebral neocortex and the CA fields of the hippocampus. Large numbers of small diameter dendrites or dendritic spines were observed in the neuropil. These made asymmetrical synaptic contacts with unlabelled axon terminals containing small round vesicles, characteristic of glutamatergic terminals. BGT-1 label was observed in an extra-perisynaptic region, away from the post-synaptic density. Immunoreactivity was not observed in portions of dendrites that formed symmetrical synapses, axon terminals, or glial cells. The distribution of BGT-1 on dendritic spines, rather than at GABAergic axon terminals, suggests that the transporter is unlikely to play a major role in terminating the action of GABA at a synapse. Instead, the osmolyte betaine is more likely to be the physiological substrate of BGT-1 in the brain, and the presence of the transporter in pyramidal neurons suggests that these neurons utilize betaine to maintain osmolarity.     

Estrogen and aging affect synaptic distribution of phosphorylated LIM kinase (pLIMK) in CA1 region of female rat hippocampus

17beta-Estradiol (E) increases axospinous synapse density in the hippocampal CA1 region of young female rats, but not in aged rats. This may be linked to age-related alterations in signaling pathways activated by synaptic estrogen receptor alpha (ER-alpha) that potentially regulate spine formation, such as LIM-kinase (LIMK), an actin depolymerizing factor/cofilin kinase. We hypothesized that, as with ER-alpha, phospho-LIM-kinase (pLIMK) may be less abundant or responsive to E in CA1 synapses of aged female rats. To address this, cellular and subcellular distribution of pLIMK-immunoreactivity (IR) in CA1 was analyzed by light and electron microscopy in young and aged female rats that were ovariectomized and treated with either vehicle or E. pLIMK-IR was found primarily in perikarya within the pyramidal cell layer and dendritic shafts and spines in stratum radiatum (SR). While pLIMK-IR was occasionally present in terminals, post-embedding quantitative analysis of SR showed that pLIMK had a predominant post-synaptic localization and was preferentially localized within the postsynaptic density (PSD). The percentage of pLIMK-labeled synapses increased (30%) with E treatment (P<0.02) in young animals, and decreased (43%) with age (P<0.002) regardless of treatment. The pattern of distribution of pLIMK-IR within dendritic spines and synapses was unaffected by age or E treatment, with the exception of an E-induced increase in the non-synaptic core of spines in young females. These data suggest that age-related synaptic alterations similar to those seen with ER-alpha occur with signaling molecules such as pLIMK, and support the hypothesis that age-related failure of E treatment to increase synapse number in CA1 may be due to changes in the molecular profile of axospinous synapses with respect to signaling pathways linked to formation of additional spines and synapses in response to E.     

Dendritic spines disappear with chilling but proliferate excessively upon rewarming of mature hippocampus

More dendritic spine synapses occur on mature neurons in hippocampal slices by 2 h of incubation in vitro, than in perfusion-fixed hippocampus. What conditions initiate this spinogenesis and how rapidly do the spines begin to proliferate on mature neurons? To address these questions, CA1 field of the hippocampus neurons expressing green fluorescent protein in living slices from mature mice were imaged with two-photon microscopy. Spines disappeared and dendrites were varicose immediately after slice preparation in ice-cold artificial cerebrospinal fluid (ACSF). Electron microscopy (EM) revealed disrupted dendritic cytoplasm, enlarged or free-floating postsynaptic densities, and excessive axonal endocytosis. Upon warming dendritic varicosities shrank and spines rapidly reappeared within a few minutes illustrating the remarkable resilience of mature hippocampal neurons in slices. When membrane impermeant sucrose was substituted for NaCl in ACSF dendrites remained spiny at ice-cold temperatures and EM revealed less disruption. Nevertheless, spine number and length increased within 30 min in warm ACSF even when the extracellular calcium concentration was zero and synaptic transmission was blocked. When slices were first recovered for several hours and then chilled in 6 degrees C ACSF many spines disappeared and the dendrites became varicose. Upon re-warming varicosities shrank and spines reemerged in the same position from which they disappeared. In addition, new spines formed and spines were longer suggesting that chilling, not the initial injury from slicing, caused the spines to disappear while re-warming triggered the spine proliferation on mature neurons. The new spines might be a substrate for neuronal recovery of function, when neurons have been chilled or exposed to other traumatic conditions that disrupt ionic homeostasis.     

Stability of dendritic spines and synaptic contacts is controlled by alpha N-catenin

Morphological plasticity of dendritic spines and synapses is thought to be crucial for their physiological functions. Here we show that alpha N-catenin, a linker between cadherin adhesion receptors and the actin cytoskeleton, is essential for stabilizing dendritic spines in rodent hippocampal neurons in culture. In the absence of alpha N-catenin, spine heads were abnormally motile, actively protruding filopodia from their synaptic contact sites. Conversely, alpha N-catenin overexpression in dendrites reduced spine turnover, causing an increase in spine and synapse density. Tetrodotoxin (TTX), a neural activity blocker, suppressed the synaptic accumulation of alpha N-catenin, whereas bicuculline, a GABA antagonist, promoted it. Furthermore, excess alpha N-catenin rendered spines resistant to the TTX treatment. These results suggest that alpha N-catenin is a key regulator for the stability of synaptic contacts.