噪声对海马CA3区神经元电活动及突触超微结构的影响

本文用电生理学方法及电镜技术研究105dB(A)白噪声对海马CA3区神经元电活动及突触超微结构的影响。结果表明:大鼠在强噪声暴露期间(5min),其神经元放电出现减频反应(占53.3％),增频反应(占20％)和基本无反应(占26.7％)。而强噪声定时重复暴露(每天1h共50天)后,单位放电频率极显著地低于对照组,以及高频单位消失而低频单位增加;同时,突触超微结构(大鼠和豚鼠)也出现小泡不集中于突触前膜和线粒体空泡化增多等不利于突触功能的变化。表明强噪声对海马CA3区神经元的影响是明显的,且以抑制性作用更为显著。本文结合本室以往工作进行讨论,认为噪声影响学习功能可能有通过影响海马的活动而作用的机制。     

学习训练对谷氨酸单钠所致大鼠海马损伤的神经保护作用

目的：探讨学习训练对谷氨酸神经毒性的保护作用。方法：在SD大鼠生后第3～9d腹腔注射谷氨酸单钠复制谷氨酸毒性模型,在1月龄和2月龄时训练大鼠学会以明暗辨别来获得食物,3月龄时取脑,在光镜下计数海马内存活神经元数,电镜下观察海马CA1区的超微结构,并计数突触数,测量突触活性带长度。结果：学习训练组海马CA3区和CA4区内的存活神经元数、海马CA1区内的突触数和突触活性带长度均大于非学习组,结论：结果提示学习训练可在一定程度上减轻MSG对海马的损伤。     

中枢神经元营养因子

脑细胞的发育和存活,同外周神经元一样,有赖于神经生长因子(NGF)、神经元存活因子(NSF)、突起伸长因子(NEF)、突起促进因子(NPF)等主要由靶组织产生的神经元营养因子的作用。由这些可溶性物质介导的神经元—神经元或神经元—非神经元间的相互作用,对中枢神经元的发育、突触的发生,以及中枢神经元的交性和再生,具有重要的理论和实际意义。     

大鼠海马神经元突触超微结构的增龄变化

目的为研究脑老化过程中学习、记忆功能减退的神经结构基础提供实验依据。方法应用透射电子显微镜,观察比较从出生1 d至24月龄（1 d、1月龄、3月龄、6月龄、18月龄、24月龄）的Sprague Dawley大鼠海马神经元突触超微结构的随增龄变化,同时观察与脑老化密切相关的指标脂褐素沉积。结果在大鼠6月龄之前,随着月龄的增加,海马神经元突触超微结构的发育逐渐完善,至6月龄大鼠突触数量明显增多;此后突触数量逐渐减少,至24月龄大鼠神经元突触数量最少。从1月龄开始海马神经元内即可见少量脂褐素颗粒沉积,随着月龄的逐渐增加,至24月龄时脂褐素颗粒沉积显著。结论青年期大鼠的海马神经元突触发育最好,进入老年期后,突触结构受损,老年期损伤最为严重,同时伴有大量的脂褐素颗粒沉积。     

横断大鼠穹窿-海马伞对其海马CA3区突触形态的影响

目的：观察横断大鼠穹窿-海马伞对其海马突触形态的影响。方法：横断大鼠双侧穹窿-海马伞（FF）建立动物模型,于手术前、后对大鼠进行迷宫检查,重点对海马CA3区多形层突触界面的结构参数进行定量分析。结果：突触界面曲率减小,突触间隙宽度加大,突触后膜致密物质厚度明显变薄,穿孔性突触的比例也有不同程度降低。结论：横断穹窿-海马伞引起海马CA3区突触形态明显改变,推测海马内Ach的正常水平对维持海马CA3区突触界面超微结构有重要作用。     

真鲷视网膜结构及其视觉特性研究：Ⅱ视网膜光感受细胞超微结构研究

对真鲷光感受细胞的超微结构进行观察,结果表明：视杆外段膜盘为游离膜盘,视锥外段膜盘则为连续的膜结构,视锥和视杆均含有连接纤毛和辅助外段。花萼状突起起源于内段。椭体内充满线粒体,无球状小体。双锥椭圆体并生膜为六层,视锥内段无鳍状突起,视锥突触带,在明适应视网膜中数量增多,在暗适应视网中数量减少,视杆突触带在这两种适应网膜中数量不变,每一杆小球只有一个突触带,而锥小足有４－６个突触带。     

东莨菪碱慢性给药大鼠作为老龄相关记忆损害模型的探索

目的对东莨菪碱慢性给药大鼠能否作为老龄相关记忆损害模型进行探索。方法14只1月龄SD大鼠随机分为对照组和东莨菪碱模型组。东莨菪碱模型组大鼠皮下注射东莨菪碱2mg kg,2次日,正常对照组予等量生理盐水,连续21d。然后利用Morris水迷宫(MWM)参照记忆试验进行行为学测试;神经元的特殊染色及电子显微镜技术,观察大鼠海马CA1、CA3区锥体细胞数、超微结构的改变以及突触可塑性变化。结果东莨菪碱组大鼠隐匿平台搜索实验成绩有一定损害;两组大鼠空间探索次数差异无显著性(P>0.05)。两组间海马CA1、CA3区锥体细胞数差异无显著性(P>0.05)。两组大鼠锥体细胞胞体超微结构无差异,但两组大鼠CA1区神经元突触超微结构有轻微变化。结论东莨菪碱慢性给药对大鼠学习记忆能力有一定损害,但对长时记忆无明显影响;对海马神经元结构无明显损害,对神经元突触可塑性有轻微影响。此种动物模型可能不是理想的老年性痴呆或老年相关记忆损害模型。     

血管性痴呆模型大鼠海马CA3区微管相关蛋白-2的表达及其意义

目的:探讨海马CA3区神经元微管相关蛋白-2(MAP-2)表达变化与学习记忆功能的关系.方法:采用大白鼠大脑中动脉线栓法(MCAO)缺血再灌模型,分为缺血2h再灌(I/R)1d、7d、14d、30d、90d组和假手术组,免疫组织化学方法观察海马CA3区MAP-2表达,并用图像分析系统作定量分析;同时用Morris水迷宫检测再灌7d、14d、30d、90d组大鼠行为学变化.结果:缺血再灌1d海马CA3区MAP-2呈高表达突起断裂不均匀,再灌7d和14d表达最高,突起出现螺旋样变,再灌30d后MAP-2的表达开始恢复,突起依然断裂,再灌90d后突起形态基本恢复正常.行为学检测发现,大白鼠缺血再灌7d和14d组定位航行试验潜伏期明显延长,空间探索试验中跨平台次数减少,再灌30d开始恢复,再灌90d与假手术组无差别.结论:缺血再灌后,海马CA3区神经元处于高度可塑性状态,可能是神经元新的突触连接形成的结构基础之一,可部分代偿缺血敏感区CA1神经元丧失引起的学习记忆功能的下降.     

亚硝基化修饰依赖的蛋白酶体降解途径可抑制细胞周期依赖性蛋白激酶5的活性

正突触间的连接受到多种蛋白质的活性与功能的协调配合,细胞周期依赖性蛋白激酶5(Cyclin-dependent kinase 5,Cdk5)的激活在突触形成过程中发挥重要作用,Cdk5的过度激活可通过减少树突棘数量及下调神经元表面受体NMDA的表达导致突触形成障碍。最近,来自香港理工大学的研究团队发现NO可对Cdk5特异性激活子p35进行亚硝基化修饰,进而介导蛋白酶体降解途径下调p35表达,降低Cdk5活性。研究人员发现,在神经元型一氧化氮合酶(nNOS)敲除小鼠中,海马神经元密度及成熟性均显著下降,神经元表面受体     

发育中脑惊厥性损伤与海马Zn2+转移

Zn^2＋是一种新的调节神经系统兴奋毒性损伤的离子型介质。积聚于海马苔藓纤维（MF）通路突触前膜囊泡内的Zn^2＋,通过特定的自稳态机制向突触后神经元转运,以此实现对大脑兴奋-抑制平衡和认知功能的调节作用。发育中长程或反复惊厥造成海马MF通路Zn^2＋的自稳态破坏,Zn^2＋在细胞内和突触间发生异常转移,并有再生性发芽等病理损伤现象。Zn^2＋转运体、Ca^2＋通透性α-氨基-3-羧基-5-甲基异恶唑-4-丙酸（AMPA）／红藻氨酸通道（Ca-A／K通道）、金属结合蛋白和线粒体等共同参与发芽过程中Zn^2＋的异常转移。除此之外,Zn^2＋亦可作为神经调质,激活信号转导通路,对突触的功能或可塑性产生微妙的影响。这一独特的离子型跨突触信使作用可能具有重要的生理和病理意义。     

The relations between neurite development and the subcellular structures of hippocampal neuron somata

The relations between neurite development and the subcellular structures of the hippocampal neuron somata have been studied with atomic force microscopy (AFM). The conformation of the neuron was achieved by the synapse-like structures found by AFM scanning along a neurite of the cell. Hippocampal neuron somata were divided into two or three subcellular parts by one or two horizontal grooves. The upper parts increased while the middle and the lower parts decreased with the number and the length of the neurites and the formation of the neurosynapse-like structures. When neurites sufficiently developed, the middle parts were lost and the lower parts became very small. Mitosis inhibitors could prevent the formation of such subcellular structures of hippocampal neuron somata, which was accompanied by the loss of ability to form synapse-like structures. These results suggest that the upper parts are responsible for neuritogenesis while the middle and the lower parts only have indirect effect on it.     

Differential but complementary mnemonic functions of the hippocampus and subiculum

In this study we describe how the hippocampus and subiculum act in concert to encode information in a spatial delayed-nonmatch-to-sample (DNMS) task. This encoding was functionally partitioned between neurons within subiculum and hippocampus to uniquely identify trial-specific information accounting for both spatial and temporal constraints on performance within and between trials. Encoding by subicular neurons in the task was normally accurate and specific, but only if delays were shorter than 15 s, whereas trial-specific information encoded by hippocampal neurons was subject to strong biases from prior trial sequences and was accessible only when delays exceeded 15 s. The two structures operated in a complementary manner to encode information correctly on 75% of all trials using the above strategies. The remaining 25% of trials were at risk due to inherent idiosyncrasies by which hippocampal and subicular neurons encoded information and became errors when the random sequence of trials conflicted with these constraints.     

Conductance transients onto dendritic spines in a segmental cable model of hippocampal neurons.

Dendritic shaft (Zd) and spine (Zsp) input impedances were computed numerically for sites on hippocampal neurons, using a segmental format of cable calculations. The Zsp values for a typical spine appended onto a dendritic shaft averaged less than 2% higher than the Zd values for the adjacent dendritic shaft. Spine synaptic inputs were simulated by a brief conductance transient, which possessed a time integral of 12 X 10(-10)S X ms. This input resulted in an average peak spine response of 20 mV for both dentate granule neurons and CA1 pyramidal cells. The average spine transient was attenuated less than 2% in conduction across the spine neck, considering peak voltage, waveform parameters, and charge transfer. The spine conductance transient resulted in an average somatic response of 100 microV in the dentate granule neurons, because of passive electrotonic propagation. The same input transient was also applied to proximal and distal sites on CA1 pyramidal cells. The predicted responses at the soma demonstrated a clear difference between the proximal and distal inputs, in terms of both peak voltage and waveform parameters. Thus, the main determinant of the passive propagation of transient electrical signals in these neurons appears to be dendritic branching rather than signal attenuation through the spine neck.     

Dynamics of retrieval strategies for remote memories

Prevailing theory suggests that long-term memories are encoded via a two-phase process requiring early involvement of the hippocampus followed by the neocortex. Contextual fear memories in rodents rely on the hippocampus immediately following training but are unaffected by hippocampal lesions or pharmacological inhibition weeks later. With fast optogenetic methods, we examine the real-time contribution of hippocampal CA1 excitatory neurons to remote memory and find that contextual fear memory recall, even weeks after training, can be reversibly abolished by temporally precise optogenetic inhibition of CA1. When this inhibition is extended to match the typical time course of pharmacological inhibition, remote hippocampus dependence converts to hippocampus independence, suggesting that long-term memory retrieval normally depends on the hippocampus but can adaptively shift to alternate structures. Further revealing the plasticity of mechanisms required for memory recall, we confirm the remote-timescale importance of the anterior cingulate cortex (ACC) and implicate CA1 in ACC recruitment for remote recall.     

The role of the supramammillary area of the hypothalamus in cognitive functions

The supramammillary area (SUM) of the hypothalamus has wide spread connection with numerous brain structures. It is known that the SUM can control the frequency of the hippocampal theta rhythm, which plays a role in the cognitive functions of the hippocampal formation. In order to examine the role of the specific cells of the SUM in learning and memory, selective cholinergic neurotoxic or excitotoxic lesioned rats of the SUM were tested for spatial memory on the Morris water maze (MWM) test. After the behavior tests, the expression of acetylcholinesterase (AChE) in the hippocampus was studied using the immunohistochemistry. In the MWM test, both lesion of the SUM with 192 IgG-saporin or ibotenic acid produced the impairment of spatial learning and memory. The expression of AChE immunreactive neurons in the hippocampal CA3 region was decreased after injections of 192 IgG-saporin into the SUM. These findings suggest that cholinoceptive cells of the SUM area may play a critical role in the process of learning and memory.     

Microcontact printing for precise control of nerve cell growth in culture

Microcontact printing, facilitated by silane linker chemistry and high-relief stamps, creates precise patterns of proteins, which in turn control growth of hippocampal neurons in culture. This additive, multi-mask technique permits several different molecules to be patterned on the same substrate. The covalent linker technology permits relatively long-term (two-week) compliance of neurons to the stamped pattern against a polyethylene glycol background. When polylysine was stamped adjacent to a laminin/polylysine mixture, neural somata and dendrites preferred the polylysine while axons prefer the mixture or the border between the two.     

Mossy fiber pathfinding in multilayer organotypic cultures of rat hippocampal slices

1. Using a novel technique of organotypic cultures, in which two hippocampal slices were cocultured in a bilayer style, we found that the mossy fibers arising from the dentate gyrus grafted onto another dentate tissue grew along the CA3 stratum lucidum of the host hippocampal slice. The same transplantation of a CA1 microslice failed to form a network with the host hippocampus.2. Thus, the type of grafted neurons is important to determine whether they can form an appropriate network after transplantation.     

Electrophysiological study of the functional connections of the hypothalamus with the forebrain in the tortoise Emys orbicularis

During stimulation of the posterior hypothalamus, the evoked potentials with short latent periods, high amplitude and poor exhaustion by rhythmic stimulation were recorded in the hippocampal cortex. In the piriform cortex, the evoked potentials exhibited longer latent periods and complex configuration. Less readily the evoked potentials appeared in the neocortex, their latency being very large. During stimulation of the anterior hypothalamus, maximum activity was also localized in the hippocampal cortex. The data obtained indicate close connection between hypothalamic structures and the hippocampal cortex. The latter is presumably the main projectional area for the ascending afferentation from the hypothalamus.     

A study on co-localization of FSH and its receptor in rat hippocampus

It has been known that GnRH, LH and their receptors exist in hippocampal neurons. However, whether FSH and its receptor also exist in hippocampal neurons remained unknown yet. In situ hybridization, double-labeled immunofluorescence stain and double-labeled immunohistochemistry stain in adjacent sections were used in our research to study the distribution, co-localization of FSH and its receptor and co-localization of FSH and GnRH receptor in rat hippocampus. The result found that pyramidal neurons from CA1 to CA4 region and granule neurons in dentate gyrus could express FSH and its receptor, majority of hippocampal neurons co-expressed FSH and its receptor, FSH and GnRH receptor. These suggested that hippocampal neurons not only express FSH but also act as FSH target cells. FSH may regulate the function of hippocampal neurons by ways of paracrine or autocrine. At the same time, GnRH may regulate the function of FSH neuron in hippocampus through GnRH receptor.