The role of estradiol and progesterone in phased synaptic remodelling of the rat arcuate nucleus

During the estrous cycle there is a phasic synaptic remodelling in the hypothalamic arcuate nucleus, consisting in a loss and regain of axo-somatic synapses during the 48 h period between the morning of proestrus and the morning of metestrus. Synaptic changes are accompanied by cyclic modifications in the number of intramembrane particles in the plasma membrane of arcuate neuronal somas. To test the effect of the ovarian steroids on arcuate axo-somatic synapses we treated castrated females either with oil vehicle, 17β-estradiol, progesterone, or a combination of estradiol and progesterone, and observed them for 48 h. The number of axo-somatic synaptic profiles showed a 33% fall by 24 h after estradiol treatment and returned to control levels by 48 h. The effect of estradiol on axo-somatic synapses was accompanied by a marked and reversible modification of the number of intramembrane particles in the plasma membrane of arcuate neuronal somas. Progesterone alone did not affect the number of axo-somatic synaptic profiles nor the number of intramembrane particles, but when administered together with estradiol, blocked the effects of estradiol on neuronal membrane and synapses.     

Cerebellar neuroblastoma

Summary A cerebellar tumor of a 4-month-old girl was examined by light and electron microscopy. The presence of numerous synaptic vesicles in many cell processes and the occasional synaptic devices warranted the diagnosis of neuroblastoma of the cerebellum. The nature of the tumor is discussed briefly.     

The role of electron microscopy in neuropathology

The electron microscope has been an essential instrument for elucidating the morphology of cells and tissue. Fine structural investigation of nervous tissue has disclosed numerous new findings, which were once invisible. In this communication I present my personal perspective on the role of electron microscopy in neuropathology through the presentation of selected electron microscopic projects engaged in our institution. These include brain edema, structural analysis of the myelin in the central nervous system, endodermal cysts in the central nervous system, aberrant synaptic development, toxoplasmosis in AIDS, and Hirano bodies.     

The CD200 and CD200 receptor cell surface proteins interact through their N-terminal immunoglobulin-like domains

CD200 (OX2) is a broadly distributed cell surface glycoprotein that interacts with a receptor on myeloid cells (CD200R) involved in regulation of macrophage function. Both CD200 and CD200R contain two Ig superfamily domains like many other leukocyte membrane proteins. Site-directed mutagenesis of CD200R showed that, like CD200, it interacted through its N-terminal domain. This indicated that the cell-cell interaction spans four Ig superfamily domains and this distance is similar to many interactions found between T cells and antigen-presenting cells. This suggests that this topology is also important in interactions of CD200 on a variety of cells with CD200R on myeloid cells, and comparable contact sites may be important mediating regulation in other cell-cell interactions. The mutagenesis showed that the binding involved the predicted GFCC' face of its N-terminal domain, like that of CD200, suggesting that the interaction evolved from a homotypic interaction.     

Cathepsin B-like proteolysis and MARCKS degradation in sub-lethal NMDA-induced collapse of dendritic spines

Sub-lethal excitotoxic injury to dendrites can elicit loss or shrinkage of dendritic spines. Here, we used a cell culture model of sub-lethal NMDA-induced injury to investigate a role for proteolysis in spine collapse. Transient incubation with NMDA-induced spine collapse and spine F-actin loss within 10 min, an effect not mimicked by the actin assembly inhibitor latrunculin A. NMDA-induced spine collapse was significantly attenuated by preincubation with broad-spectrum cysteine protease inhibitors. Results obtained using several class-specific protease inhibitors suggested that this protective effect was due to specific blockade of cathepsin B/L type protease activity, since selective inhibitors of only these proteases significantly attenuated spine loss. Cathepsin B-like immunoreactivity was observed at synaptic sites, but lysosomes were not. Immunoblot analysis showed that MARCKS (myristoylated-alanine-rich C-kinase substrate), a known substrate of cathepsin B, was specifically degraded in response to intense NMDA receptor stimulation. This effect was blocked by preincubation with a cathepsin B-selective inhibitor. Together these data suggest a model in which NMDA-induced spine collapse involves cathepsin B-like proteolysis of MARCKS, and possibly other proteins that regulate the actin-based cytoskeleton.     

Association of GRIP1 with a GABA(A) receptor associated protein suggests a role for GRIP1 at inhibitory synapses

GABA(A) receptors mediate the majority of fast synaptic inhibition in the mammalian central nervous system. GABA(A) receptors associate with a number of cytosolic proteins important for regulating their function including the GABA(A) receptor gamma2 subunit associated protein GABARAP. Here we show GABARAP associates with the synaptic PDZ domain containing protein GRIP1. GRIP1 has been localized to inhibitory synapses however the role of this protein with respect to neuronal inhibition remains unclear. Using in vitro protein interaction assays we show that GABARAP interacts directly with PDZ domains 4-6 of GRIP1. Furthermore, using coimmunoprecipitation assays we show that GABARAP interacts with GRIP1 in vivo. Finally, we show that GRIP1 colocalizes with gamma2 subunit containing GABA(A) receptors in cultured hippocampal neurons. Our findings provide evidence that GRIP1 can associate with proteins important for regulating GABA(A) receptor function and suggest that GRIP1 may play a role at inhibitory synapses.     

LKB1表达下调对培养海马神经元突触mEPSC的影响

目的研究离体培养的海马神经元LKB1表达下调对于神经元微小兴奋性突触后电流(mEP-SC)的影响。方法选用17d的胚胎大鼠培养海马神经元,分别用电穿孔的方法转染CAG-RE质粒和LKB1RNAi质粒,培养10~12d后进行电生理记录,选用全细胞膜片钳方式及自由记录模式,细胞外液加TTX阻断动作电位,加Bicucullin抑制GABA电流,记录神经元的mEPSC,比较2组神经元的mEPSC频率和幅度的差别。结果转染CAG-RE的神经元mEPSC幅度平均为25.6pA,频率平均为(5.21±0.25)Hz,是基线的99.8%;转染LKB1RNAi的神经元mEPSC幅度平均为35.1pA,频率平均为(5.79±0.27)Hz,是基线的127.1%;比较2组间频率、幅度变化,差别有显著性意义(P<0.05)。结论LKB1基因表达下调增强了培养海马神经元突触传递的效率。     

Participation of Golgi neuron processes in the cerebellar glomeruli: An electron microscope study

Summary Synaptic relations, within the cerebellar isles, of Golgi II neuron axons and dendrites have been studied in the cat. Golgi axon endings can be identified with some probability in the outer (cortical) zone of the cerebellar glomeruli in normal material. They can well be recognized in the chronically isolated folium in which mossy fibers have completely degenerated. The Golgi axons are very thin preterminal fibers with small enlargements containing synaptic vesicles and contacting the preterminal intraglomerular parts of the granule cell dendrites as well as their terminal spheroid protrusions. The spheroid protrusions of the granule dendrites are the main postsynaptic loci of the granule neuron having their main synapse with the mossy fiber — generally of central position in the glomerulus — and additional synapses, more often on their outer surface, with the Golgi axons. No significant difference is seen between the two contacts, from which one is known to be excitatory (mossy) and the other inhibitory (Golgi ax.). The Golgi cell has also descending dendrites, known from light microscopy to be engaged in the cerebellar isles. By tracing these dendrites from the cell bodies and using their characteristic short finger-like processes as a criterion for their identification, the synapses between mossy endings and Golgi dendrites could be identified under the EM. They are broad contacts between a dendrite passing along one side of the mossy ending, with several synaptic attachment plaques and with small dendritic processes protruding into invaginations of the mossy ending. — The cerebellar glomerulus is thus a complex synaptic apparatus with two different axonal elements (mossy and Golgi endings) and often two dendritic elements (granule and Golgi dendrites) involved. — The possible functional significance of the Golgi cell is discussed in the light of these findings and the new discoveries by Eccles et al. (1964b, 1966) on its inhibitory nature.     

胎儿及成人大脑皮质颞叶突触超微结构的形态学观察与分析

目的：观察胎儿及成人大脑皮质颞叶突触的超微结构并进行统计学分析。方法：经常规生物样本制备方法制成切片常规电子染色，H600电镜下观察突触超微结构。结果与结论：突触的数量、类型、形态随胎龄的增加有明显的变化，并与成人比较有显著性差异。     

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。