生后早期大鼠海马NMDA受体亚单位NR1、NR2A和NR2B的表达变化

运用免疫组织化学反应和图象分析处理技术研究生后 1d、4d、1周、2周、3周、4周、5周、6周的 SD大鼠海马结构中NMDA受体亚单位 NR1、NR2 A、NR2 B三种蛋白质的表达变化规律。结果表明 ,生后各时间点海马结构各区锥体细胞及颗粒细胞胞体中均有 NR1、NR2 A、NR2 B的表达 ,NR2 B还在锥体细胞的顶树突中有较强表达。 NR1与 NR2 B的生后表达变化模式相似 ,在生后 1d和 4d,两者在 CA3区的表达均高于 CA1 区 ;生后 1周后两者在 CA1 区的表达则高于 CA3区 ;到生后 2～ 3周其表达达到峰值。而 NR2 A却与此不同 ,生后 1d、4d时其在海马结构各区的表达较高 ,随发育时间延长表达逐渐下降 ,大约在生后 4周降至谷底。整个发育过程中 ,NR1在海马结构各区的表达始终高于 NR2 A和 NR2 B的表达。这些结果提示 ,生后早期大鼠海马结构 NR1、NR2 A、NR2 B的表达具有发育性时空差异和亚单位差异 ,这种差异可能与发育早期海马学习功能的特异性以及海马各区对缺血敏感性不同有关。     

NMDA受体亚单位在海马脑片和在体发育海马结构中表达变化的比较

目的：对比长期培养大鼠海马脑片与在体生后发育海马结构中N-甲基-D-天冬氨酸(NMDA)受体亚单位NR1、NR2A和NR2B表达变化的异同,为利用海马脑片研究NMDA受体亚单位在生理和病理状态中的作用提供资料。方法：免疫组织化学染色、海马脑片培养技术及图像分析。结果：NRI、NR2B在海马脑片各区和生后大鼠海马结构各区表达模式相似,均呈“先升、后降”的趋势,但升降幅度不同;NR2A在海马脑片各区是“先升、后降”的趋势,在生后海马结构各区则呈现“先降后升”的模式。NRI、NR2A、NR2B在脑片和在体发育海马的相似期间,在CA1、CA3、PG区表达均无显著性差异。结论：P3w／C2w时NRI和NR2B在海马脑片各区的表达强度,和其在生后大鼠海马结构中的表达较相似。     

NR1、NR2A与PSD-95在生后大鼠海马发育中的表达

目的:探讨N-甲基-D-天冬氨酸受体亚单位1(N-methy1-D-aspartate receptor subunit1,NR1)、N-甲基-D-天冬氨酸受体亚单位2A(N-methy1-D-aspartate receptor subunit2A,NR2A)与突触后密度蛋白-95(Postsynapticdensity protein 95,PSD-95)在Wistar大鼠海马生后发育过程中的表达。方法:应用免疫荧光染色方法检测NR1、NR2A与PSD-95在生后不同时期大鼠海马CA1、CA3区和齿状回(DG)中的表达情况。结果:NR1于生后各期海马CA1、CA3区和DG的表达均增强,P14~P21达高峰期后减弱。NR2A于生后在海马CA1和CA3区的表达略有减弱,P4后增强至高峰期P14,然后轻微减弱,在DG中NR2A的表达生后略有减弱,P4后在增强的趋势中于P7、P14和P28后均有不同程度的减弱,高峰期在P28。PSD-95于生后各期海马CA1、CA3区和DG的表达均增强,P21~P28达高峰期后轻微减弱。结论:NR1、NR2A和PSD-95在CA1、CA3区和DG中的表达具有特异的时空分布模式,此模式可能与其在生后发育中发挥的不同生理功能相关。     

NR2B反义寡核苷酸对大鼠海马CA1区NR2B mRNA表达的影响

目的：观察NMDA受体2B亚单位（NR2B）反义寡核苷酸（ANR2B）对海马CA1区NR2B mRNA表达的影响,筛选有效的ANR2B,探讨改变NR2B mRNA表达的新方法.方法：正常SD大鼠,海马CA1区立体定位注射ANR2B,灌注取脑,连续冰冻切片,原位杂交组织化学方法染色,光镜下观察NR2B mRNA在ANB2B作用下的表达变化.结果：正常大鼠海马CA1区立体定位注射ANR2B后,注射点及其周围NR2B mRNA原位杂交染色强度明显下降,仅有少量锥体细胞和颗粒细胞散在分布;而在注射NR2B正义寡核苷酸（SNR2B）、生理盐水（NS）及NS插针不注射（NSNO）的海马切片上,海马CA1区的染色特征与注射ANR2B有明显差别,其作用区锥体细胞、颗粒细胞及顶树突的NR2B原位杂交染色强度无明显变化.结论：ANR2B能够降低NR2B mRNA在正常大鼠海马CA1区的基础性高表达.     

前脑缺血再灌流后大鼠海马NMDA受体亚单位NR2A和NR2B蛋白质表达的变化

用免疫组织化学和图像处理方法 ,观察分析了大鼠前脑缺血 15 min后再灌流 2 h～ 7d的海马结构各区域 NMDA受体亚单位 NR2 A和 NR2 B的表达变化规律及其差异 ,藉以探讨二者在缺血性脑损伤中的作用。结果显示 :( 1) NR2 A在 CA1 区和CA3 区的表达于再灌早期表现为小幅度下降 ( P<0 .0 5 ) ,此趋势在 CA3 区可以逆转 ;但在 CA1 区逐渐加剧 ,第 7d时降至 2 1% ,NR2 A在齿状回的表达几无改变 ;( 2 )与 NR2 A不同 ,再灌后 2 h,NR2 B在 CA1 区的表达即较对照组增高 ( P<0 .0 5 ) ,并持续到再灌后 2 4h,之后转而急剧下降 ,至第 7d仅余 11% ;在 CA3 区及齿状回 ,再灌后 6～ 48h,NR2 B的表达也较对照组增高 ( P<0 .0 5 ) ;在再灌后 72 h则恢复至对照组水平。结果提示 ,缺血性脑损伤后 NR2 A和 NR2 B表达变化的不同可能是造成 CA1 区、CA3区及齿状回缺血敏感性差异的一个重要原因     

NR2B反义寡核苷酸对脑缺血海马CA1区NR2B蛋白质表达的影响

目的：观察前脑缺血后NR2B反义寡核苷酸（ANR2B）对海马CA1区NR2B蛋白质表达的影响,为临床脑血管疾病的防治以及研制特异性新药提供理论基础。方法：正常SD大鼠,脑缺血手术48h前海马CA1区分别立体定位预注射ANR2B、NR2B正义寡核苷酸（SNR2B）。后行四动脉阻断全脑缺血手术,免疫组织化学反应,观察NR2B蛋白质在ANR2B的作用下的表达变化。结果：海马CA1区立体定位注射ANR2B后,注射区及其周围NR2B免疫组织化学染色强度明显下降,仅有少量锥体细胞散在分布。结论：ANR2B可以在体局部抑制缺血早期NR2B亚单位蛋白表达上升趋势。     

Bcl-2、Bax蛋白在NRs抗体预处理后缺氧缺糖海马脑片CA_1区的表达变化

运用海马脑片培养技术、海马脑片缺氧缺糖方法、免疫组织化学染色和图像分析处理技术观察用 NMDA受体亚单位抗体预处理后再缺氧缺糖的海马脑片 CA1 区 Bcl-2和 Bax蛋白的表达变化 ,以探究其亚单位与海马脑片缺氧缺糖性损伤的关系。结果显示 ,各实验组海马脑片 CA1 区均有不同程度 Bcl-2、Bax蛋白表达和细胞缺失形成的空洞。 Bcl-2蛋白在 NR1+ OGD组、NR2 A+ OGD组和 NR2 A + NR2 B+ OGD组 CA1 区的表达均明显弱于 OGD组 (3组均 P<0 .0 5 ) ;其在 NR2 B+ OGD组和HOTC组的表达则强于 OGD组 (两者 P<0 .0 5 )。 Bax蛋白在 NR1+ OGD组、NR2 A+ OGD组和 NR2 A+ NR2 B+ OGD组的表达均强于 OGD组 (NR2 A+ OGD组 P<0 .0 5 ) ;在 NR2 B+ OGD组和 HOTC组其表达则明显弱于 OGD组 (后者 P<0 .0 5 )。结论 :单纯缺氧缺糖可引起海马脑片 CA1 区锥体细胞的迟发性损伤 ,同时引起 Bcl-2蛋白和 Bax蛋白的表达变化 ;预加 NMDA受体亚单位 NR1、NR2 A抗体和 NR2 A+ NR2 B抗体可以加重缺氧缺糖性海马脑片 CA1 区细胞损伤程度 ;预加 NR2 B抗体则可减轻其损伤程度。提示 NMDA受体亚单位成分的变化可以调节 Bcl-2和 Bax蛋白在缺氧缺糖性海马脑片 CA1 区的表达 ,从而调节CA1 区神经元的损伤程度     

短暂性前脑缺血后大鼠海马各区NMDA受体亚单位NR2A和NR2B mRNA的表达变化

应用原位杂交组织化学和图像处理与分析的方法 ,观察短暂性前脑缺血 (15 m in)再灌注 (0 .5 h～ 7d)大鼠海马各区NR2 A和 NR2 B m RNA的表达变化 ,探讨二者在缺血性脑损伤中的作用。结果发现 ,缺血后 ,NR2 A和 NR2 B m RNA在海马各区呈现出一种相对一致的表达。在海马 CA1 区 ,NR2 A和 NR2 B m RNA的表达分别在缺血再灌 6h和 12 h降至低谷 (P<0 .0 5 ) ,然后表达开始回升 ,在缺血再灌 48h都升至高峰 (P<0 .0 5 ) ,之后表达再次下降 ,直至缺血后 7d(P<0 .0 5 ) ;在海马 CA3区 ,二者的表达变化规律与 CA1 区相似 ,不同的是表达变化的幅度明显减小。在齿状回 ,缺血后 0 .5 h～ 72 h,NR2 A和 NR2 B m RNA的表达未见显著性变化 ,72 h后表达开始下降 ,直至缺血后 7d(P<0 .0 5 )。以上结果提示 ,短暂性前脑缺血后 ,NR2 A和 NR2 B m R-NA在大鼠海马各区表达变化的模式不同 ,这种不同可能与海马的选择性易损现象和迟发性细胞死亡有关     

离体培养人神经干细胞中NMDA受体亚单位NR2A和NR2B的表达

目的:研究早期离体培养的人胚胎海马神经干细胞(NSCs)中NMDA受体亚单位NR2A和NR2B的表达。方法:取胎龄8～12周人胚脑海马,进行NSCs分离、培养、传代和鉴定。通过免疫细胞化学和RT-PCR等方法检测传代1次和2次的人胚胎海马NSCs中NMDA受体亚单位NR2A和NR2B的蛋白和mRNA表达。结果:自孕8～12周人胚脑海马分离培养的NSCs,NMDA受体亚单位NR2A和NR2B免疫细胞化学反应呈阳性,这两种受体亚单位的mRNA均被检测到。结论:体外培养的早期人胚胎海马NSCs能稳定表达NMDA受体亚单位NR2A和NR2B。     

慢性复合应激对大鼠学习与记忆及海马NMDA受体亚基NR2A和NR2B表达的影响

为了观察慢性复合应激对大鼠学习与记忆的影响和海马内 NMDA受体亚基 NR2 A、NR2 B表达的变化。本研究将成年雄性 Wistar大鼠分为实验组和对照组 ,实验组动物每天交替暴露于复合应激原环境中达 6周 ,用 Morris水迷宫和 Y迷宫作业测试其空间学习与记忆成绩 ,再采用免疫组织化学和图像处理方法分析海马 CA1 、CA3、齿状回区的 NR2 A和 NR2 B的表达。结果显示 :( 1) Morris水迷宫测试 :慢性复合应激组大鼠寻找平台的潜伏期较对照组明显缩短 ,Y迷宫测试 :慢性复合应激组大鼠学会躲避电击的正确次数较对照组明显增多 ;( 2 )慢性复合应激组海马内 NMDA受体亚基 NR2 B表达水平较对照组明显上调 ,NR2 A表达水平无显著变化。结论 :慢性复合应激可增强学习与记忆能力 ,NMDA受体表达变化可能是影响学习与记忆的机制之一     

Subunit-specific gating controls rat NR1/NR2A and NR1/NR2B NMDA channel kinetics and synaptic signalling profiles

NR2A and NR2B are the predominant NR2 NMDA receptor subunits expressed in cortex and hippocampus. The relative expression level of NR2A and NR2B is regulated developmentally and these two subunits have been suggested to play distinct roles in long-term synaptic plasticity. We have used patch-clamp recording of recombinant NMDA receptors expressed in HEK293 cells to characterize the activation properties of both NR1/NR2A and NR1/NR2B receptors. Recordings from outside-out patches that contain a single active channel show that NR2A-containing receptors have a higher probability of opening at least once in response to a brief synaptic-like pulse of glutamate than NR2B-containing receptors (NR2A, 0.80; NR2B, 0.56), a higher peak open probability (NR2A, 0.50; NR2B, 0.12), and a higher open probability within an activation (NR2A, 0.67; NR2B, 0.37). Analysis of the sequence of single-channel open and closed intervals shows that both NR2A- and NR2B-containing receptors undergo multiple conformational changes prior to opening of the channel, with at least one of these steps being faster for NR2A than NR2B. These distinct properties produce profoundly different temporal signalling profiles for NR2A- and NR2B-containing receptors. Simulations of synaptic responses demonstrate that at low frequencies typically used to induce long-term depression (LTD; 1 Hz), NR1/NR2B makes a larger contribution to total charge transfer and therefore calcium influx than NR1/NR2A. However, under high-frequency tetanic stimulation (100 Hz; > 100 ms) typically used to induce long-term potentiation (LTP), the charge transfer mediated by NR1/NR2A considerably exceeds that of NR1/NR2B.     

Activation of NR1/NR2B NMDA receptors

N-methyl-D-aspartate (NMDA) receptors are highly expressed in the central nervous system and are involved in excitatory synaptic transmission as well as synaptic plasticity. Despite considerable structural and biophysical research, the mechanism behind activation of the NMDA receptor is still poorly understood. By analyzing patch clamp recordings of one channel activated by glutamate, we determined the burst structure and open probability for recombinant rat NR1/NR2B receptors. We used partial agonists at the glutamate and glycine binding sites to show that at least two kinetically distinct subunit-associated conformational changes link co-agonist binding to the opening of the NMDA receptor pore. These data suggest that NR1 and NR2B subunits, respectively, undergo a fast and slow agonist-dependent conformational change that precedes opening of the pore. We propose a new working model of receptor activation that can account for macroscopic as well as microscopic NMDA receptor properties.     

Temperature dependence of NR1/NR2B NMDA receptor channels

N-methyl-D-aspartate (NMDA) receptors are highly expressed in the CNS, mediate the slow component of excitatory transmission and play key roles in synaptic plasticity and excitotoxicity. These ligand-gated ion channels are heteromultimers composed of NR1 and NR2 subunits activated by glycine and glutamate. In this study, patch-clamp recordings were used to study the temperature sensitivity of recombinant NR1/NR2B receptors expressed in human embryonic kidney (HEK) 293 cells. Rate constants were assessed by fitting a six-state kinetic scheme to time courses of transient macroscopic currents induced by glutamate at 21.9-46.5 degrees C. Arrhenius transformation of the rate constants characterizing NMDA receptor channel activity indicates that the most sensitive were the rate constants of desensitization (temperature coefficient Q(10)=10.3), resensitization (Q(10)=4.6) and unbinding (Q(10)=3.6). Other rate constants and the amplitude of single-channel currents were less temperature sensitive. Deactivation of responses mediated by NR1/NR2B receptors after a brief application of glutamate was best fit by a double exponential function (tau(fast): Q(10)=3.7; tau(slow): Q(10)=2.7). From these data, we conclude that desensitization/resensitization of the NMDA receptor and glutamate unbinding are especially temperature sensitive and imply that at physiological temperatures the channel kinetics play an important role in determining amplitude and time course of NMDA receptor-mediated postsynaptic currents and these receptors mediated synaptic plasticity.     

Zinc inhibition of rat NR1/NR2A N-methyl-D-aspartate receptors

Zinc ions (Zn²⁺) are localized in presynaptic vesicles at glutamatergic synapses and released in an activity-dependent manner. Modulation of NMDA-type glutamate receptors by extracellular Zn²⁺ may play an important role under physiological conditions and during pathologies such as ischaemia or seizure. Zn²⁺ inhibits NMDA receptors containing the NR2A subunit with an IC₅₀ value in the low nanomolar concentration range. Here we investigate at the single-channel level the mechanism of high affinity Zn²⁺ inhibition of recombinant NR1/NR2A receptors expressed in HEK293 cells. Zn²⁺ reversibly decreases the mean single-channel open duration and channel open probability determined in excised outside-out patches, but has no effect on single-channel current amplitude. A parallel series of experiments demonstrates that lowering extracellular pH (increasing proton concentration) has a similar effect on NR1/NR2A single-channel properties as Zn²⁺. Fitting the sequence of single-channel events with kinetic models suggests that the association of Zn²⁺ with its binding site enhances proton binding. Modelling further suggests that protonated channels are capable of opening but with a lower open probability than unprotonated channels. These data and analyses are consistent with Zn²⁺-mediated inhibition of NMDA receptors primarily reflecting enhancement of proton inhibition.     

NR2C and NR2D subunits of NMDA receptors in frog and turtle retina

Glutamate NMDA (N-methyl-d-aspartate) receptors are widely distributed in the central nervous system where they are involved in cognitive processes, motor control and many other functions. They are also well studied in the retina, which may be regarded as a biological model of the nervous system. However, little is known about NR2C and NR2D subunits of NMDA receptors, which have some specific features as compared to other subunits. Consequently the aim of the present study was to investigate their distribution in frog (Rana ridibunda) and turtle (Emys orbicularis) retinas which possess mixed and cone types of retina respectively. The experiments were performed using an indirect immunofluorescence method. Four antibodies directed to NR2C and NR2D subunits of NMDA receptor, as well as three antibodies directed to different splice variants of NR1 subunit, which is known to be obligatory for proper functioning of the receptor, were applied. All antibodies caused well expressed labeling in frog and turtle retinas. The NR2C and NR2D subunits were localized in glial Müller cells, while the NR1 subunit had both neuronal and glial localization. Our results show that glial NMDA receptors differ from neuronal ones in their subunit composition. The functional significance of the NMDA receptors and their NR2C and NR2D subunits, in particular for the neuron-glia interactions, is discussed.     

Functional NR2B- and NR2D-containing NMDA receptor channels in rat substantia nigra dopaminergic neurones

NMDA receptors regulate burst firing of dopaminergic neurones in the substantia nigra pars compacta (SNc) and may contribute to excitotoxic cell death in Parkinson's disease (PD). In order to investigate the subunit composition of functional NMDA receptors in identified rat SNc dopaminergic neurones, we have analysed the properties of individual NMDA receptor channels in outside-out patches. NMDA (100 n m ) activated channels corresponding to four chord conductances of 18, 30, 41 and 54 pS. Direct transitions were observed between all conductance levels. Between 18 pS and 41 pS conductance levels, direct transitions were asymmetric, consistent with the presence of NR2D-containing NMDA receptors. Channel activity in response to 100 n m or 200 μ m NMDA was not affected by zinc or TPEN ( N,N,N',N '-tetrakis-[2-pyridylmethyl]-ethylenediamine), indicating that SNc dopaminergic neurones do not contain functional NR2A subunits. The effect of the NR2B antagonist ifenprodil was complex: 1 μ m ifenprodil reduced open probability, while 10 μ m reduced channel open time but had no effect on open probability of channels activated by 100 n m NMDA. When the concentration of NMDA was increased to 200 μ m , ifenprodil (10 μ m ) produced the expected reduction in open probability. These results indicate that NR2B subunits are present in SNc dopaminergic neurones. Taken together, these findings indicate that NR2D and NR2B subunits form functional NMDA receptor channels in SNc dopaminergic neurones, and suggest that they may form a triheteromeric NMDA receptor composed of NR1/NR2B/NR2D subunits.     

Antagonist properties of eliprodil and other NMDA receptor antagonists at rat NR1A/NR2A and NR1A/NR2B receptors expressed in Xenopus oocytes

We have studied the effects of a variety of N-methyl-

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-aspartate (NMDA) antagonists acting at different sites of the NMDA receptor complex on NMDA-induced currents in Xenopus oocytes expressing heteromeric NR1A/NR2A and NR1A/NR2B receptors. The polyamine site antagonists eliprodil (IC₅₀=3.0 μM) and ifenprodil (IC₅₀=0.27 μM) antagonized NMDA responses at NR1A/NR2B receptors but not at NR1A/NR2A receptors (IC₅₀>100 μM). The channel blockers dizocilpine, memantine and phencyclidine (PCP) were equally potent antagonists at both receptor subtypes whereas dextromethorphan was four times more potent at NR1A/NR2A receptors. The glycine site antagonists

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-689,560 and 7-Cl-kynurenate were 10 times more potent at NR1A/NR2A than at NR1A/NR2B receptor subtypes. The selectivity of eliprodil and ifenprodil for the NR1A/NR2B receptor subtype may, at least partially, explain their favorable side effect profile.     

Immunocytochemical study of NR1, NR2A and NR2B subunits of NMDA receptor in frog retina (Rana ridibunda)

The NMDA receptors are ionotropic glutamate receptors that are involved in a variety of functions in the nervous system and in particular in the retina. They are composed of NR1 and NR2 subunits. The NMDA receptors have been fairly well studied in the retina of mammals, however, there is only limited information concerning these receptors in the retinas of lower vertebrates. The aim of the present study was to investigate immunocytochemically the NR1, NR2A and NR2B subunits of the NMDA receptors in the frog retina. Six primary antibodies were used. Three of them were directed to different splice variants of the NR1 subunit and the remaining three variants directed to NR2 subunits. All antibodies showed well expressed labeling in the frog retina. The labels had a punctate character and were located mainly in the inner and the outer plexiform layers. The results obtained indicate that the NR1, NR2A and NR2B subunits of NMDA receptor may participate in the glutamatergic neurotransmission from photoreceptors to second order retinal neurons, as well as from bipolar cells to third order retinal neurons. It has been proposed that in the frog retina, several subtypes of NMDA receptors exist each involved with different functions.