大鼠海马神经元模拟缺血时谷氨酸诱发电流改变

目的：观察大鼠海马神经元模拟缺血时谷氨酸诱发电流的改变，探讨脑缺血神经元损伤的兴奋毒性机制，为中枢神经损伤的康复提供理论依据。方法：以原代培养的大鼠海马神经元为标本，采用全细胞膜片钳方法观察原代培养大鼠海马神经元模拟缺血时谷氨酸诱发电流改变。结果：当钳制电压为-60mV时，100μmol／L的N-甲基-D-天门冬氨酸(NMDA)、α-氨基-3羟基-5-甲基-4-异恶唑丙酸(AMPA)分别诱发一内向电流(INMDA、IAMPA)，模拟缺血处理后的神经元INMDA，IAMPA明显增大。结论：升高的兴奋性氨基酸激活突触后膜的兴奋性氨基酸受体后引起神经细胞损伤。     

急性缺氧对大鼠海马神经元N-甲基-D-天门冬氨酸诱发电流的影响

目的:研究N-甲基-D-天门冬氨酸(N-methyl-D-asparate,NMDA)在大鼠海马神经元上诱发电流的特性以及急性缺氧对大鼠海马神经元NMDA诱发电流(INMDA)的影响。方法:运用常规全细胞膜片钳技术,在原代培养第七八天的大鼠海马神经元上记录INMDA,并建立神经细胞体外急性缺氧模型,由Clampex8.0软件采样系统获得的图形,直接进入Clampfit8.0软件处理数据。结果:①在钳制电压为-60mV时,100μmol/LNMDA可在海马神经元上诱发出一大的内向电流,INMDA的峰值为(-745.461±123.731)pA。I-V曲线显示在钳制电压为正值时INMDA呈外向电流,而钳制电压为负值时则为内向电流。给予NMDA后,海马神经元上即刻诱发出内向电流,随后尽管持续给药20s,但INMDA开始发生衰减。②在钳制电压为-60mV时,海马神经元急性缺氧2min后,细胞外给予100μmol/LNM-DA可诱发一大而增强的INMDA,峰值为(-1670.49±202.09)pA,峰值显著增大(t=12.572,P<0.01),峰值增加率为130%。结论:NMDA诱发的电流呈现明显的内向整流性和失敏特性,急性缺氧能提高海马神经元NMDA通道的兴奋性,NMDA受体参与了兴奋毒性的产生。     

急性缺氧对大鼠海马神经元N-甲基-D-天门冬氨酸诱发电流的影响

目的：研究N-甲基-D-天门冬氨酸(N—methyl—D—asparate，NMDA)在大鼠海马神经元上诱发电流的特性以及急性缺氧对大鼠海马神经元NMDA诱发电流(INMDA)的影响。方法：运用常规全细胞膜片钳技术，在原代培养第七八天的大鼠海马神经元上记录INMDA。并建立神经细胞体外急性缺氧模型，由Clampex 8．0软件采样系统获得的图形，直接进入Clampfit 8．0软件处理数据。结果：①在钳制电压为-60mV时，100μmol／L NMDA可在海马神经元上诱发出一大的内向电流，INMDA的峰值为(-745．461&;#177;123．731)pA。I—V曲线显示在钳制电压为正值时INMDA呈外向电流，而钳制电压为负值时则为内向电流。给予NMDA后，海马神经元上即刻诱发出内向电流，随后尽管持续给药20s，但INMDA开始发生衰减。②在钳制电压为-60mV时，海马神经元急性缺氧2min后，细胞外给予100μmol／L NMDA可诱发一大而增强的INMDA峰值为(-1670．49&;#177;202．09)pA，峰值显著增大(t=12．572，P&;lt;0．01)，峰值增加率为130％。结论：NMDA诱发的电流呈现明显的内向整流性和失敏特性，急性缺氧能提高海马神经元NMDA通道的兴奋性，NMDA受体参与了兴奋毒性的产生。     

吗啡对大鼠海马神经元突触传递的作用及机制

目的从离子通道角度研究吗啡对中枢神经系统兴奋性及抑制性突触传递的作用,以探讨吗啡镇痛机制.方法原代培养新生Wistar大鼠的海马神经元.采用膜片钳技术研究吗啡对其兴奋性及抑制性突触后电流及谷氨酸诱发电流的影响.结果①吗啡可明显增强海马神经元兴奋性突触传递,加吗啡后自发兴奋性突触后电流发放频率增加了207.8%(t=42.182 8,P＜0.01).此作用可被阿片受体阻断剂纳洛酮阻断;②吗啡对微小兴奋性突触后电流的发放频率及谷氨酸诱发电流的幅度没有明显影响(t=0.962,t=0.791,P＞0.05);③吗啡可明显抑制神经元自发抑制性突触后电流,纳洛酮可拮抗吗啡作用(P＜0.01).结论吗啡对海马神经元的兴奋作用不是由于吗啡直接作用于兴奋性氨基酸-谷氨酸突触传递过程,而是可能由于抑制了抑制性中间神经元,间接产生的兴奋达到镇痛作用.     

胶质细胞源性神经营养因子对大鼠海马神经元N-甲基-D-天冬氨酸诱发电流的保护作用

目的：研究N-甲基-D-天冬氨酸(N-methyl-D-asparate，NMDA)在大鼠海马神经元上诱发电流的特性以及胶质细胞源性神经营养因子(glial cell line-derived neurotrophic factor，GDNF)对大鼠海马神经元NMDA诱发电流(INMDA)的影响。方法：实验于2002-10／2003-02在解放军第二军医大学膜片钳研究室进行，运用常规全细胞膜片钳技术，在原代培养第七八天的大鼠海马神经元上记录INMDA，以及GDNF对INMDA的影响，由Clampex 8．0软件采样系统获得的图形，直接进入Clampfit8．0软件处理数据。结果：NMDA可在海马神经细胞上诱发出大的内向离子流。当钳制电压为-60mV时，细胞外单独给予GDNF(0．1，1．0，10．0μg／L)对静息膜电导及电压门控离子通道无影响。但细胞外同时给予NMDA(100μmol／L)和GDNF(10μg／L)时，INMDA的峰值为(-578．238&;#177;100.493)pA，INDMA的峰值被抑制( t=-7．248，P&;lt;0．01)，峰值受抑制率为(21．502&;#177;7．898)％。洗去GDNF后，抑制作用消失。结论：NMDA诱发的电流呈现出明显的内向整流特性，GDNF能抑制海马神经元NMDA通道的兴奋性，从而发挥神经保护作用。     

胶质细胞源性神经营养因子对大鼠海马神经元N-甲基-D-天冬氨酸诱发电流的保护作用

目的:研究N-甲基-D-天冬氨酸N-methyl-D-asparate,NMDA在大()鼠海马神经元上诱发电流的特性以及胶质细胞源性神经营养因子(glialcellline-derivedneurotrophicfactor,GDNF)对大鼠海马神经元NMDA诱发电流(IN)的影响。MDA方法:实验于2002-10/2003-02在解放军第二军医大学膜片钳研究室进行,运用常规全细胞膜片钳技术,在原代培养第七八天的大鼠海马神经元上记录IN,以及GDNF对INMDAMDA的影响,由Clampex8.0软件采样系统获得的图形,直接进入Clampfit8.0软件处理数据。结果:NMDA可在海马神经细胞上诱发出大的内向离子流。当钳制电压为-60mV时,细胞外单独给予GDNF(0.1,1.0,10.0μg/L)对静息膜电导及电压门控离子通道无影响。但细胞外同时给予NMDA(100μmol/L)和GDNF10μg/L时,IN()MDA的峰值为(-578.238±100.493)pA,INMDA的峰值被抑制(t=-7.248,P<0.01),峰值受抑制率为(21.502±7.898)%。洗去GDNF后,抑制作用消失。结论:NMDA诱发的电流呈现出明显的内向整流特性,GDNF能抑制海马神经元NMDA通道的兴奋性,从而发挥神经保护作用。     

吗啡对大鼠海马神经元突触传递的作用及机制

目的：从离子通道角度研究吗啡对中枢神经系统兴奋性及抑制性突触传递的作用，以探讨吗啡镇痛机制。方法：原代培养新生Wistar大鼠的海马神经元。采用膜片钳技术研究吗啡对其兴奋性及抑制性突触后电流及谷氨酸诱发电流的影响。结果：①吗啡可明显增强海马神经元兴奋性突触传递，加吗啡后自发兴奋性突触后电流发放频率增加了207．8％(t=42．1828，P&;lt;0．01)。此作用可被阿片受体阻断剂纳洛酮阻断；②吗啡对微小兴奋性突触后电流的发放频率及谷氨酸诱发电流的幅度没有明显影响(t=0．962，t=0．791，P&;gt;0．05)；③吗啡可明显抑制神经元自发抑制性突触后电流，纳洛酮可拮抗吗啡作用(P&;lt;0．01)。结论：吗啡对海马神经元的兴奋作用不是由于吗啡直接作用于兴奋性氨基酸-谷氨酸突触传递过程，而是可能由于抑制了抑制性中间神经元，间接产生的兴奋达到镇痛作用。     

栝楼桂枝颗粒抗缺血性脑卒中大鼠神经元及原代海马神经元凋亡研究

目的:观察栝楼桂枝颗粒(GLGZG)抗缺血性脑卒中大鼠神经元及原代海马神经元凋亡的作用,探讨其作用机制,为其治疗脑卒中提供依据。方法:建立谷氨酸诱导原代海马神经元兴奋性毒性损伤模型、大鼠脑缺血再灌注损伤模型,采用MTT、LDH法测定GLGZG对原代海马神经元细胞活性和LDH活性的影响,采用Western Blot、Real-time PCR检测GLGZG对原代海马神经元及大鼠海马组织中Caspase-3、Bcl-2、Bax m RNA及蛋白表达水平的影响。结果:用不同浓度(100μg/m L、200μg/m L、300μg/m L)的GLGZG分别作用于原代海马神经元24 h,3个剂量组细胞存活率较谷氨酸组细胞存活率升高,其中GLGZG 200μg/m L、300μg/m L 2组细胞活力显著升高(P0.05,P0.01);3个剂量组LDH活力较谷氨酸组显著降低,其中GLGZG 200μg/m L、300μg/m L 2组可显著抑制谷氨酸损伤神经元LDH的释放(P0.05,P0.01)。GLGZG 200μg/m L、300μg/m L 2组干预后,与谷氨酸组比较可显著降低原代海马神经元Caspase-3 m RNA、Bax m RNA的表达(P0.05,P0.01),升高Bcl-2 m RNA的表达(P0.05),蛋白表达的趋势与m RNA相似;GLGZG组与模型组比较,可降低大鼠海马组织Caspase-3、Bax蛋白的表达(P0.05或P0.01),升高Bcl-2蛋白的表达(P0.01)。结论:GLGZG对缺血性脑卒中大鼠及原代海马神经元有一定的保护作用,其保护作用与其抗细胞凋亡作用有关。     

激动或阻断N-甲基-D天冬氨酸受体对大鼠脑海马兴奋性氨基酸释放的影响

目的:应用清醒大鼠脑微透析技术,观察N-甲基-D-天冬氨酸受体激动剂和阻断剂对大鼠海马兴奋性氨基酸释放的影响,探讨N-甲基-D-天冬氨酸受体对大鼠海马兴奋性氨基酸释放的自身调节作用。方法:实验于2003-12在锦州医学院药理教研室完成。45只雄性SD大鼠,横跨海马背部植入一自制的透析探头,待大鼠清醒后24h用人造脑脊液,N-甲基-D-天冬氨酸250,500μmol/L,N-甲基-D-天冬氨酸500μmol/L+MK-801100μmol/L,MK-801100μmol/L,甘氨酸500μmol/L,7-氯犬尿烯酸200μmol/L灌流,灌流速度为5μL/min,每20min收集一次透析液,采用邻苯二甲醛-β-巯基乙醇衍生化反相梯度洗脱荧光检测透析液中谷氨酸和天冬氨酸的水平。结果:45只大鼠均进入结果分析。海马内局部灌流N-甲基-D-天冬氨酸250,500μmol/L可明显增加细胞外基础状态下谷氨酸和天冬氨酸的水平。非竞争性N-甲基-D-天冬氨酸受体拮抗剂MK-801(100μmol/L)可拮抗N-甲基-D-天冬氨酸(500μmol/L)引起的谷氨酸释放增加作用。单独应用MK-801(100μmol/L)对基础状态下谷氨酸的水平没有影响。局部灌流N-甲基-D-天冬氨酸受体协同激动剂甘氨酸500μmol/L也可明显增加细胞外基础状态下谷氨酸的水平。局部灌流N-甲基-D-天冬氨酸上甘氨酸部位的选择性阻断剂7-氯犬尿烯酸200μmol/L可以拮抗甘氨酸引起的谷氨酸释放增加作用。结论:兴奋性氨基酸受体N-甲基-D-天冬氨酸受体的激活增加海马内兴奋性神经递质的释放,这种N-甲基-D-天冬氨酸受体可能存在于突触前膜(兴奋性神经末梢膜上),即自身调节受体正反馈调节兴奋性氨基酸的释放。     

高功率微波辐射对大鼠脑内神经递质及全身儿茶酚胺代谢的影响

目的:观察高功率微波辐射对大鼠脑内氨基酸类神经递质及全身儿茶酚胺代谢的影响。方法:实验于2004-09/12解放军军事医学科学院放射与辐射医学研究所实验病理研究室完成。选择6～8周二级雄性Wistar大鼠60只,随机抽签法分为假辐射组(n=10)和辐射组(n=50)。辐射组按照辐射剂量分为3mW/cm2亚组(n=10)、10mW/cm2亚组(n=20)、30mW/cm2亚组(n=10)和100mW/cm2亚组(n=10)。采用0,3,10,30和100mW/cm2高功率微波辐射大鼠,于辐射后6h、1d和7d活杀取材,通过高效液相色谱仪检测大脑皮质、海马和丘脑中谷氨酸、天冬氨酸、γ-氨基丁酸和甘氨酸4种氨基酸的含量以及尿中香草扁桃酸和高香草酸含量的变化。结果:参加实验大鼠60只,均进入结果分析。①高功率微波辐射后6h大鼠不同脑区氨基酸类神经递质含量的变化:大脑皮质,10mW/cm2组谷氨酸及γ-氨基丁酸含量升高,谷氨酸/γ-氨基丁酸比值降低;海马3～100mW/cm2组谷氨酸含量均显著降低。丘脑中4种氨基酸含量无明显改变。②高功率微波10mW/cm2辐射不同时间后大鼠不同脑区氨基酸类神经递质含量的变化:辐射后6h大脑皮质谷氨酸含量升高,1d后基本恢复正常;γ-氨基丁酸含量明显升高,1d后有所恢复,7d时仍未恢复正常;谷氨酸/γ-氨基丁酸比值显著降低,1d后有所恢复,7d时仍未恢复正常。海马内谷氨酸含量明显降低;甘氨酸含量在辐射后6h明显降低,1d时基本恢复。丘脑氨基酸含量无明显改变。③高功率微波辐射后尿中儿茶酚胺代谢产物含量的变化:辐射后3d,10mW/cm2组尿中香草扁桃酸含量显著升高,30和100mW/cm2组显著降低;10mW/cm2组尿中高香草酸含量于显著降低;而100mW/cm2组显著升高。结论:高功率微波辐射可引起大鼠氨基酸类和儿茶酚胺类神经递质代谢紊乱,大脑皮质和丘脑均可见主要兴奋性和抑制性氨基酸含量升高,二者比值下降,提示兴奋性氨基酸参与了大脑皮质和丘脑的早期损伤,而抑制性氨基酸则与其病变恢复有关。海马兴奋性氨基酸含量及谷氨酸/γ-氨基丁酸比值均降低,提示海马神经元的兴奋性降低,可能与学习记忆能力的降低密切相关。     

Ethanol inhibits alpha-amino-3-hydyroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function in central nervous system neurons by stabilizing desensitization

Ethanol actions on alpha-amino-3-hydyroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors were studied using voltage-clamp recordings from mouse cortical and hippocampal neurons. During whole-cell recordings ethanol (EtOH) inhibited AMPA receptor-mediated currents in a dose-dependent manner at concentrations from 10 to 500 mM. The steady-state component of AMPA-activated current was more sensitive to EtOH than the peak component. To examine the effect of EtOH on a well resolved peak current component, patches were excised from cultured cortical neurons, to which AMPA and EtOH were applied using a piezoelectric solution application system. Under this condition, the peak current was not inhibited significantly by EtOH. To further study possible mechanisms of EtOH inhibition, kainate and AMPA were used to evoke currents in the absence and presence of cyclothiazide. Ethanol inhibition was stronger when receptors were activated by low than high kainate concentrations. Cyclothiazide reduced inhibition by EtOH regardless of the agonist used to activate the receptor. Finally, EtOH inhibition was reduced in a point mutated (L497Y) GluRAi receptor that lacks desensitization. These findings suggest that EtOH inhibits AMPA receptors by stabilizing the desensitized state. Our results can explain some of the variation observed in EtOH inhibition in previous studies, and support the idea that physiologically relevant concentrations of EtOH can have a strong effect on AMPA receptor function.     

全细胞记录急性分离海马锥体神经元电压门控通道电流

背景:海马是涉及学习、记忆的重要脑区,已有研究者描述了急性分离海马神经元的方法。但这些方法需要多种酶联合使用、分离过程复杂。目的:建立一种适用于膜片钳研究,简单、快速地分离海马神经元的方法。设计:动物实验观察。单位:西安交通大学医学院生理与病理生理学系。材料:实验于2004-03/10在西安交通大学医学院医学实验中心完成。实验动物选用出生10～15d的Sprague-Dawley大鼠,性别不限。方法:急性分离海马神经元;应用全细胞记录模式记录延迟整流钾电流以及电压门控钙电流。主要观察指标:观察急性分离海马神经元的形态;记录海马神经元延迟整流钾电流、电压门控钙电流。结果:①倒置显微镜观察急性分离的神经元具有光滑、透亮的表面,胞体呈锥体性,有一个较长的顶树突和几个基树突。②分离过程未破坏其电生理特性,钳制电压-90mV,给予时程200ms,阶跃10mV,由-70～ 20mV去极化脉冲刺激激活钙电流得到电压门控钙电流。钳制电压-80mV,给予-50mV时程50ms去极化预刺激失活瞬时外向钾电流,再给予时程200ms,阶跃10mV,由-60mV至 50mV去极化脉冲刺激激活钾电流,得到延迟整流钾电流。结论:本方法分离的神经元,适合应用膜片钳技术进行离子通道研究。     

Alteration of Na+ currents in dorsal root ganglion neurons from rats with a painful neuropathy.

Increased excitability of primary sensory neurons may be important for the generation of neuropathic pain from nerve injury. The currents underlying the action potentials of these neurons are largely carried by Na+, and changes in Na+ currents have been postulated to contribute to this increased excitability. Using patch clamp in whole-cell mode, we recorded Na+ currents from DRG neurons freshly isolated from rats with a chronic constriction injury (CCI), an animal model of neuropathic pain. We found significant changes in Na+ currents after CCI when cell size and Na+ channel properties were used to segregate DRG neurons. Most changes were concentrated in small neurons (< or = 25 microm diameter) and in the slow TTX-resistant current that is predominant in these cells. CCI produced two principal changes in these cells: it shifted the voltage-dependence of activation of the TTX-resistant current to more negative potentials and it reduced the average density of this current. The decrease in density appears to be primarily due to the decrease in the number of small neurons expressing this current. The net result is a change in both activation and steady-state inactivation properties of the total Na+ current to more negative potentials without a significant change in the density of total Na+ current. The change in activation properties of the TTX-resistant Na+ current are similar to those produced by some hyperalgesic autacoids, and may contribute to the increase in primary afferent excitability and hyperalgesia that occurs after this lesion.     

姜黄素通过新型蛋白激酶-θ亚型抑制大鼠海马神经元中通道的研究

目的探讨姜黄素对Ca2+通道电流的选择性抑制作用。方法使用10 mmol/L的钡离子作为电荷载体,利用膜片钳技术记录大鼠海马神经元的全细胞电流;免疫印迹法检测大鼠海马神经元中蛋白激酶C(PKC)的分型;进行全细胞膜片钳技术分析。结果姜黄素浓度依赖性抑制高电压门控Ca2+通道电流(IBa),姜黄素对Ca2+型通道的激活无显著影响,但能够使Ca2+通道的失活曲线向超极化方向移动;此外,在体外培养的大鼠海马神经元中,细胞内应用PKC-θ的抑制肽PKC-θ-IP,能消除黄素诱导抑制的作用;新型PKC-δ、PKC-ε和PKC-θ,但不包括PKC-η在神经元中内源性表达。结论姜黄素在大鼠海马神经元中通过新型的PKC-θ依赖途径抑制IBa,这个结论可能有利于证明姜黄素的神经保护作用。     

BIIR 561 CL: a novel combined antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and voltage-dependent sodium channels with anticonvulsive and neuroprotective properties.

Antagonists of glutamate receptors of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype, as well as of voltage-gated sodium channels, exhibit anticonvulsive and neuroprotective properties in vivo. One can postulate that a compound that combines both principles might be useful for the treatment of disorders of the central nervous system, like focal or global ischemia. Here, we present data on the effects of dimethyl-(2-[2-(3-phenyl-[1,2, 4]oxadiazol-5-yl)-phenoxy]ethyl)-amine hydrochloride (BIIR 561 CL) on neuronal AMPA receptors and voltage-dependent sodium channels. BIIR 561 CL inhibited AMPA receptor-mediated membrane currents in cultured cortical neurons with an IC50 value of 8.5 microM. The inhibition was noncompetitive. In a cortical wedge preparation, BIIR 561 CL reduced AMPA-induced depolarizations with an IC50 value of 10.8 microM. In addition to the effects on the glutamatergic system, BIIR 561 CL inhibited binding of radiolabeled batrachotoxin to rat brain synaptosomal membranes with a Ki value of 1.2 microM. The compound reduced sodium currents in voltage-clamped cortical neurons with an IC50 value of 5.2 microM and inhibited the veratridine-induced release of glutamate from rat brain slices with an IC50 value of 2.3 microM. Thus, BIIR 561 CL inhibited AMPA receptors and voltage-gated sodium channels in a variety of preparations. BIIR 561 CL suppressed tonic seizures in a maximum electroshock model in mice with an ED50 value of 2.8 mg/kg after s.c. administration. In a model of focal ischemia in mice, i.p. administration of 6 or 60 mg/kg BIIR 561 CL reduced the area of the infarcted cortical surface. These data show that BIIR 561 CL is a combined antagonist of AMPA receptors and voltage-gated sodium channels with promising anticonvulsive and neuroprotective properties.     

Calcitonin gene-related peptide enhances TTX-resistant sodium currents in cultured dorsal root ganglion neurons from adult rats

The neuropeptide calcitonin gene-related peptide (CGRP) binds to a subpopulation of dorsal root ganglion (DRG) neurons, elevates intracellular calcium, and causes inward currents in about 30% of lumbar DRG neurons. Using whole-cell patch clamp recordings, we found in the present study that application of CGRP to isolated and cultured DRG neurons from the adult rat enhances voltage-gated TTX-resistant (TTX-R) Na(+) inward currents in about 30% of small- to medium-sized DRG neurons. During CGRP, peak densities of Na(+) currents increased significantly. CGRP shifted the membrane conductance of the CGRP-responsive cells towards hyperpolarization without changing the slope of the peak conductance curve. The effect of CGRP was blocked by coadministration of CGRP8-37, an antagonist at the CGRP receptor. The effect of CGRP was also blocked after bath application of PKA14-22, a membrane-permeant blocker of protein kinase A, and PKC19-31, a PKC inhibitor, in the recording pipette. These data show pronounced facilitatory effects of CGRP on TTX-R Na(+) currents in DRG neurons which are mediated through CGRP receptors and intracellular pathways involving protein kinases A and C. Thus, in addition to prostaglandins, CGRP is another mediator that affects TTX-R Na(+) currents which are thought to occur mainly in nociceptive DRG neurons.     

Nitrous oxide inhibits glutamatergic transmission in spinal dorsal horn neurons

The effects of nitrous oxide (N2O) are thought to be mediated by several pharmacological pathways at different levels of the central nervous system. Here, we focus on excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord with respect to its importance for the nociceptive processing. The effects of 50% N2O on electrically evoked and spontaneous excitatory glutamatergic transmission and on the response to exogenous administration of N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptor agonists were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. Peak amplitudes of Adelta- and C-fiber evoked monosynaptic NMDA- and AMPA-receptor-mediated excitatory postsynaptic currents (EPSCs) were decreased in the presence of N2O. N2O reduced the peak amplitude and integrated area of exogenous NMDA- and AMPA-induced currents. Moreover N2O changed the distribution of miniature EPSC amplitude, but not frequency distribution in most neurons. N2O inhibits glutamatergic transmission in the superficial dorsal horn by modulating the NMDA- and AMPA-receptors. Our findings raise the possibility that the antinociceptive effect of N2O may be directly mediated at the level of the spinal cord.     

Ethanol suppresses fast potentiation of glycine currents by glutamate

Excitatory (glutamate) and inhibitory (GABA(A) and glycine) receptor/channels coexist in many neurons. To assess effects of ethanol on the interaction of glutamate and glycine receptors, glycine-induced current (I(Gly)) was recorded by a whole-cell patch-clamp technique from neurons freshly dissociated from the ventral tegmental area of rats. A conditioning prepulse of glutamate (1-3 s, 1 mM) significantly and reversibly potentiated responses to a pulse of glycine. This potentiation was increased when extracellular calcium was raised to 12 mM and reduced by including 10 mM 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in the internal recording medium. It was not affected by 5 microM 1-N,O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62), a selective inhibitor of calcium/calmodulin-dependent protein kinase II. In a concentration-response analysis, a conditioning pulse of glutamate significantly lowered the EC(50) for glycine and increased the maximal I(Gly). Kinetic analysis of the currents indicated that glutamate slowed deactivation of glycine-gated chloride channels; therefore, glutamate may increase the affinity of glycine receptors for glycine. When coapplied with glycine, ethanol (10 mM) potentiated I(Gly) in 35% of neurons from the ventral tegmental area. In contrast, when coapplied with glutamate and glycine, ethanol suppressed the glutamate-induced potentiation of I(Gly) in these neurons. This suppression was also observed when ethanol and glycine were coapplied after a glutamate prepulse. A similar effect was observed when ethanol alone did not potentiate I(Gly). These findings suggest that glutamate-induced calcium influx modulates glycine receptors by a mechanism that can be blocked by ethanol.     

Characterization of two novel N-methyl-D-aspartate antagonists: EAA-090 (2-[8,9-dioxo-2,6-diazabicyclo [5.2.0]non-1(7)-en2-yl]ethylphosphonic acid) and EAB-318 (R-alpha-amino-5-chloro-1-(phosphonomethyl)-1H-benzimidazole-2-propanoic acid hydrochloride)

Two novel N-methyl-d-aspartate (NMDA) antagonists with unique chemical structures, EAA-090 (2-[8,9-dioxo-2, 6-diazabicyclo[5.2.0]non-1(7)-en2-yl]ethylphosphonic acid) and EAB-318 (R-alpha-amino-5-chloro-1-(phosphonomethyl)-1H-benzimidazole-2-propanoic acid hydrochloride), were compared with CGS-19755 (Selfotel) in ligand binding, electrophysiology, and neuroprotection assays. CGS-19755, EAA-090 and EAB-318 inhibited [(3)H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding to NMDA receptors with IC(50) values of 55, 28, and 7.9 nM, respectively. All three compounds decreased the duration of spontaneous synaptic currents and inhibited NMDA-activated currents in rat hippocampal neurons. IC(50) values for inhibition of current induced by 10 microM NMDA were 795, 477, and 69 nM for CGS-19755, EAA-090, and EAB-318, respectively. The NMDA antagonists protected chick embryo retina slices and cultured rat hippocampal and cortical neurons from glutamate- and NMDA-induced neurotoxicity. In experiments in which different NMDA receptor splice variants and subtypes were expressed in Xenopus oocytes, all three antagonists preferentially blocked NMDA-elicited currents mediated by N-methyl-d-aspartate receptor (NR)1 splice variants containing the N-terminal insertion. They also favored NR2A-versus NR2B- or NR2C-containing NMDA receptors, with EAA-090 showing the greatest selectivity. EAA-090 was 10 times more potent at blocking NR2A-versus NR2B- or NR2C-containing NMDA receptors. In addition to being the most potent NMDA antagonist, EAB-318 inhibited alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors. The combination of NMDA and AMPA/kainate block enabled EAB-318 to protect neurons against ischemia induced cell death.     

Down-regulation of synaptic GluN2B subunit-containing N-methyl-D-aspartate receptors: a physiological brake on CA1 neuron α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hyperexcitability during benzodiazepine withdrawal

A significant link was previously established between benzodiazepine withdrawal anxiety and a progressive increase in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) potentiation in hippocampal CA1 neurons from rats withdrawn up to 2 days from 1-week oral administration of the benzodiazepine flurazepam (FZP). Despite AMPAR current potentiation, withdrawal anxiety was masked by a 2-fold reduction in CA1 neuron N-methyl-D-aspartate receptor (NMDAR) currents since preinjection of an NMDA antagonist restored NMDAR currents and unmasked anxiety in 2-day FZP-withdrawn rats. In the current study, GluN subunit levels in postsynaptic density (PSD)-enriched subfractions of CA1 minislices were compared with GluN2B-mediated whole-cell currents evoked in CA1 neurons in hippocampal slices from 1- and 2-day FZP-withdrawn rats. GluN1 and GluN2B, although not the phosphoSer1303-GluN2B ratio or GluN2A subunit levels, were decreased in PSD subfractions from 2-day, but not 1-day, FZP-withdrawn rats. Consistent with immunoblot analyses, GluN2B-mediated NMDAR currents evoked in slices from 2-day FZP-withdrawn rats were decreased in the absence, but not the presence, of the GluN2B subunit-selective antagonist ifenprodil. In contrast, ifenprodil-sensitive NMDAR currents were unchanged in slices from 1-day withdrawn rats. Because AMPA (1 μM) preincubation of slices from 1-day FZP-withdrawn rats induced depression of GluN2B subunit-mediated currents, depression of NMDAR currents was probably secondary to AMPAR potentiation. CA1 neuron NMDAR currents were depressed ～50% after 2-day withdrawal and offset potentiation of AMPAR-mediated currents, leaving total charge transfer unchanged between groups. Collectively, these findings suggest that a reduction of GluN2B-containing NMDAR may serve as a homeostatic feedback mechanism to modulate glutamatergic synaptic strength during FZP withdrawal to alleviate benzodiazepine withdrawal symptoms.