吗啡对大鼠海马神经元突触传递的作用及机制探讨

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并探讨其机制。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 (sEPSC)的发放频率增加了 ( 2 0 7.8± 2 0 .9) %。此作用可被阿片受体阻断剂纳洛酮阻断 (P <0 .0 1) ;②吗啡对微小兴奋性突触后电流 (mEPSC)的发放频率及谷氨酸诱发电流的幅度没有明显影响 (P >0 .0 5 ) ;③吗啡可明显抑制神经元自发抑制性突触后电流 (sIPSC) ,纳洛酮可拮抗吗啡作用 (n =13 ,P <0 .0 1)。结论 :实验结果提示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 ,间接产生的兴奋作用。     

低频刺激后海马CA1区场兴奋性突触后电位与群体锋电位的变化

在大鼠海马脑片上使用双电极在CA1区进行细胞外记录 ,观察低频刺激 (LFS)诱发同突触长时程抑制 (LTD)时场兴奋性突触后电位 (fEPSP)的斜率 (S EPSP)和群体锋电位 (PS)的幅值 (A PS)的变化。给予 90 0脉冲 1HzLFS后 ,S EPSP和A PS降低的幅度分别是 35 4± 5 3%和 6 8 0± 7 2 % ;而给予 4 5 0脉冲 1HzLFS后 ,S EPSP和A PS分别降低 14 3± 2 3%和 36 8± 6 7%。上述两组中A PS的变化率均显著大于S EPSP (P <0 0 1) ,而 90 0脉冲数组中两个指标的变化率均大于 4 5 0脉冲数组 (P <0 0 5 )。高Mg2 + (4mmol/L)使突触的传递活动减弱 ,但不影响LTD的诱发 ,在高Mg2 + 介质中 ,LFS引起的A PS变化率仍显著大于S EPSP (P <0 0 1)。结果表明 ,由LFS诱发同突触LTD的水平不仅与LFS的脉冲数有关 ,还与评价指标的选择有关     

在体大鼠海马CA1区侧枝/联合纤维通路和TA通路的不同EPSP空间整合特性

在麻醉Wistar大鼠上,结合脑室给药,应用双电极刺激技术刺激海马独立的两条侧枝／联合纤维通路、TA通路,并在CA1区放射层记录兴奋性突触后电位（EPSP）,对海马CA1区锥体细胞近、远端树突EPSP的空间整合进行了初步探讨。结果表明,海马CA1区锥体细胞近、远端树突的空间整合都是亚线性的;近端树突的空间整合不受期望值大小的影响,但远端树突的空间整合随期望值增加而减小（更趋于亚线性）。此外,荷包牡丹碱没有影响EPSP的空间整合;但瞬时A型钾通道（IAK^＋）的拮抗剂氨基吡啶-4却使得近端树突的空间整合趋于线性发展。本研究表明,海马CA1锥体细胞近、远端树突不同的被动、主动特征使它们具有了不同的空间整合特性。由于近端树突接受海马内部侧枝／联合纤维投射的信息,远端树突通过TA通路接受内嗅皮层投射的信息,由此提示,CA1区锥体细胞对来自海马内部和直接来自皮层的信息输入采用了不同的整合方式。     

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。     

通脉益智方对VD大鼠学习记忆行为和海马CA1区突触结构的影响

目的:观察通脉益智方对血管性痴呆模型大鼠学习记忆行为和海马CA1区突触超微结构的影响.方法:应用高脂血症大鼠,采用脑缺血再灌注的方法建立血管性痴呆动物模型,利用跳台实验和Y型迷宫实验检验大鼠的学习记忆能力,应用透射电镜和光镜观察分析海马CA1区神经细胞和突触形态结构的变化.结果:跳台实验和Y型迷宫实验表明模型大鼠学习记忆能力明显下降,而给予通脉益智方组学习记忆能力改善,与模型组相比有显著性差异(p＜0.05).形态学观察显示模型组大鼠海马CA1区神经细胞排列紊乱,核固缩、退化、变性、坏死、消失.突触结构不完整,突触小泡减少;突触间隙模糊,线粒体肿胀、空泡样变.通脉益智方组的神经细胞、突触的形态与模型组相比有明显改善.结论:通脉益智方通过减轻突触的损伤及对神经细胞的保护作用,从而改善了学习记忆能力.     

大鼠海马CA3区的习得性长时程突触增强

本实验应用慢性埋植电极技术以电生理学结合行为学的方法,观察大鼠条件性饮水反应的建立、消退和再建立过程中,其海马CA_3区突触效应的变化规律。以刺激内嗅区的穿通纤维(PP)诱发的单突触的群体锋电位(PS)及群体兴奋性突触后电位(EPSPs)为指标,经叠加处理分析,发现随着条件反应的建立,海马CA_3锥体细胞出现突触效应的长时程增强(LTP),它随行为反应的实验性消退而消退,而在随后再次建立条件反应时,又重新出现;且无论此LTP达最高水平还是它的完全消退均超前于条件性行为反应的水平。又在一个实验日训练作业结束时PS并未立即随之增大,在24h内它随时间而发展,但到第4小时已达最高水平,且条件反应率是与PS的水平相应的,对PS与EPSPs的斜率进行相关分析表明,PS的变化主要是突触传递功效的变化。上述结果表明,海马CA_3区随着行为训练有习得性LTP产生。从其发神变化特点及其与条件性行为的关系,提示此习得性LTP极其可能是本实验中学习和记忆的展经基础。     

在饮水条件反射中大鼠海马CA3区突触效应的变化

我们的工作表明,大鼠在明暗辨别学习过程中海马齿状回有习得性长时程增强(Long-term potentiation,LTP)现象,又CA_3区在大鼠学习和记忆过程有重要作用。本实验观察大白鼠海马CA_3区锥体细胞在条件性饮水反应的建立、巩固和消退过程中其突触效应的变化规律,以进一步探讨习得性LTP的特性,及从突触水平探讨海马CA_3区在学习记忆功能中的作用。     

四逆散对PTSD及睡眠障碍大鼠海马CA1/CA3区神经元动作电位的影响

目的：研究四逆散对创伤后应激障碍（PTSD）及睡眠障碍大鼠海马CA1/CA3区神经元动作电位的影响。方法：SD雄性大鼠50只随机分为5组：空白组、生理盐水组、模型组、四逆散组和帕罗西汀组（n=10）。空白组和生理盐水组正常饲养,其他组用幽闭电击法复制PTSD模型,生理盐水组每天灌胃给予生理盐水10 ml/kg,模型组于造模前1 h灌胃生理盐水10 ml/kg,帕罗西汀组和四逆散组分别于造模前1 h灌胃盐酸帕罗西汀4.2 mg/kg和四逆散2.41 g/kg进行处理,每天1次,连续7 d,造模和干预同时进行。使用在体多通道神经信号采集系统,采集大鼠海马CA1/CA3区神经元动作电位。结果：生理盐水组与空白组大鼠海马CA1/CA3区动作电位发放均多为发散状,且脉冲较密集。与生理盐水组相比,模型组大鼠海马CA1/CA3区动作电位发放脉冲较稀少,电位发放呈簇状。与模型组相比,帕罗西汀组、四逆散组动作电位发放脉冲稍多,呈发散状。与空白组比较,生理盐水组大鼠海马CA1/CA3区平均峰电位发放速率无明显差异,提示灌胃刺激对大鼠海马CA1/CA3区平均峰电位发放速率影响不明显。模型组大鼠海马CA1/CA3区平均峰电位发放速率显著低于生理盐水组,表明幽闭电击能明显抑制海马CA1/CA3区平均峰电位发放速率。与模型组相比,四逆散组和帕罗西汀组大鼠海马CA1/CA3区平均峰电位发放速率均显著升高,提示两药物对PTSD大鼠海马CA1/CA3区单位时间峰电位发放速率有明显调节作用。结论：四逆散对大鼠海马CA1/CA3区神经元时空特性损害有明显的改善作用。     

戊四氮点燃癫痫大鼠空间学习记忆改变及海马突触素、突触后致密物PSD-95表达的变化

目的探讨戊四氮点燃癫痫对大鼠空间学习记忆的影响及可能的分子机制。方法戊四氮(pentylenetet-razol,PTZ)点燃建立慢性癫痫(chronic epileptic,CEP)模型,Morris水迷宫进行行为学检测,免疫组织化学方法观察大鼠海马CA1、CA3区突触素(synaptophysin,P38)和突触后致密物95(postsynaptic density 95,PSD-95)的表达,并用计算机图像分析系统对免疫反应结果进行处理。结果水迷宫试验检测癫痫组大鼠空间学习记忆能力受损;免疫组化结果表明其海马CA1、CA3区P38和PSD-95免疫反应产物较对照组明显减少(P<0.01,P<0.05)。结论戊四氮点燃癫痫大鼠伴有学习记忆功能减退,其海马神经元P38和PSD-95的表达减少可能参与了空间学习记忆受损。     

The sodium current underlying action potentials in guinea pig hippocampal CA1 neurons

Neurons were acutely dissociated from the CA1 region of hippocampal slices from guinea pigs. Whole-cell recording techniques were used to record and control membrane potential. When the electrode contained KF, the average resting potential was about -40 mV and action potentials in cells at -80 mV (current-clamped) had an amplitude greater than 100 mV. Cells were voltage-clamped at 22-24 degrees C with electrodes containing CsF. Inward currents generated with depolarizing voltage pulses reversed close to the sodium equilibrium potential and could be completely blocked with tetrodotoxin (1 microM). The amplitude of these sodium currents was maximal at about -20 mV and the amplitude of the tail currents was linear with potential, which indicates that the channels were ohmic. The sodium conductance increased with depolarization in a range from -60 to 0 mV with an average half-maximum at about -40 mV. The decay of the currents was not exponential at potentials more positive than -20 mV. The time to peak and half-decay time of the currents varied with potential and temperature. Half of the channels were inactivated at a potential of -75 mV and inactivation was essentially complete at -40 to -30 mV. Recovery from inactivation was not exponential and the rate varied with potential. At lower temperatures, the amplitude of sodium currents decreased, their time course became longer, and half-maximal inactivation shifted to more negative potentials. In a small fraction of cells studied, sodium currents were much more rapid but the voltage dependence of activation and inactivation was very similar.     

Dose-dependent effects of phencyclidine on hippocampal CA1 neurons

The dose-dependent effects of phencyclidine were examined in guinea pig hippocampal slices using intracellular and extracellular recordings. Orthodromically evoked population potentials from the CA1 cell body layer were enhanced by low doses (0.2-0.4 microM) and depressed by high doses (0.01-10 mM). Medium doses of the drug (2.0-10.0 microM) showed little effect. Intracellular recordings from CA1 pyramidal neurons gave similar dose-dependent results. Low doses increased spontaneous firing rates and caused silent cells to fire. Medium doses both increased and decreased firing rates, whereas high doses depressed firing rates. Large transient depolarizing shifts were seen in some phencyclidine-treated cells at medium and high doses. Phencyclidine effects took 15-30 min to develop and were only partially reversible after a washout of up to 1 h.     

Varenicline and nicotine enhance GABAergic synaptic transmission in rat CA1 hippocampal and medial septum/diagonal band neurons

AimsThe FDA approved smoking cessation aid varenicline can effectively attenuate nicotine-stimulated dopamine release. Varenicline may also exert important actions on other transmitter systems that also influence nicotine reinforcement or contribute to the drug's cognitive and affective side effects. In this study, we determined if varenicline, like nicotine, can stimulate presynaptic GABA release.Main methodsUsing whole-cell patch-clamp techniques, we measured GABA_AR-mediated asynchronous, spontaneous miniature inhibitory postsynaptic currents (mIPSCs) in acute brain slices from two brain regions important for learning and memory, the hippocampus and basal forebrain.Key findingsBoth varenicline (10 μM) and nicotine (10 μM) applications alone resulted in small but significant increases in amplitude, as well as robustly enhanced frequency of mIPSCs in hippocampal CA1 pyramidal neurons and medial septum/diagonal band (MS/DB) neurons. A unique subpopulation of MS/DB neurons showed decreases in frequency. In the presence of nicotine, varenicline effectively attenuated the expected enhancement of hippocampal mIPSC frequency like a competitive antagonist. However, in the MS/DB, varenicline only partially attenuated nicotine's effects. Reversing the order of drug application by adding nicotine to varenicline-exposed slices had little effect.SignificanceVarenicline, like nicotine, stimulates presynaptic GABA release, and also exerts a partial agonist action by attenuating nicotine-stimulated release in both the hippocampus and basal forebrain. These effects could potentially affect cognitive functions.     

Potassium channel blocker-induced presynaptic modulation of inhibitory synaptic transmission in hippocampal neurons of rats

The effects of blockers of voltage-gated potassium channels, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), on inhibitory postsynaptic currents (IPSC) evoked by local electrical stimulation of zones of unitary synaptic terminals on hippocampal neurons were studied using a voltage-clamp technique under conditions of low density cell culture. At activation of the transmitter release in the absence of action potentials (when the terminals are in a tetrodotoxin-containing medium), external application of 5 mM 4-AP reversibly increased the averaged IPSC amplitude by 90±30%, while a similar effect of 10 mM TEA reached only 20±7%. The amplitudes of individual evoked IPSC varied between 10 and more than 150 pA. Amplitude histograms of IPSC in all studied neurons (n=14) were of a polymodal nature and could not described by a Gaussian law. An increase in the averaged IPSC amplitude under the influence of potassium channel blockers cannot be described as resulting only from modification of the number of trials without transmitter release (blank events). The mechanism of potassium channel blocker-induced facilitation of IPSC evoked by single synaptic terminals is discussed.     

Temperature dependence of synaptic responses in guinea pig hippocampal CA1 neurons in vitro

1. Temperature-dependent properties of synaptic transmission were studied by recording orthodromic responses of the population spike and excitatory postsynaptic potential in CA1 pyramidal neurons of guinea pig hippocampal slices.2. Increasing the temperature of the perfusing medium from 30 to 43°C resulted in a decrease in the amplitude of the population spike (A-PS) and a reduced slope of the excitatory postsynaptic potential (S-EPSP). Bath application of the -aminobutyric acid receptor antagonist, picrotoxin, or a change in the calcium concentration of the perfusate did not affect the A-PS during heating.3. Increasing the strength of the synaptic input to that eliciting a PS with an amplitude 50, 75, or 100% of maximal at 30°C resulted in a significant increase in the A-PS during the middle phase of hyperthermia (35–39°C).4. The long-term potentiation (LTP) induced at either 30 or 37°C showed the same percentage increase in both the amplitude of the population spike and the S-EPSP after delivery of a tetanus (100 Hz, 100 pulses) to CA1 synapses.5. The results of the present study, therefore, indicate that the decrease in CA1 field potential was linearly related to the temperature of the slice preparation, while LTP was induced in these responses during heating from 30 to 37°C.     

Age-related changes in synaptic vesicle pools of axo-dendritic synapses on hippocampal CA1 pyramidal neurons in mice

The ultrastructure of symmetric (putatively inhibitory) axo-dendritic synapses on the membrane of hippocampal CA1 pyramidal neurons was investigated in young (20-day-old) and adult (1-year-old) mice. It was shown that synapses of adult animals contain, on average, fewer synaptic vesicles (SVs), and resting SVs of the reserve pool are mostly responsible for this difference. At the same time, in the synapses of adult mice SVs are localized closer to active zones, and the readily releasable pool of SVs is larger in these animals than in young mice. The observed changes in the spatial structure of SV pools presumably demonstrate the age-associated adaptation of inhibitory synapses providing the maintenance of adequate functional properties of hippocampal neuronal networks. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 407–411, September–December, 2006.     

Modulatory effects of oligodendrocytes on the conduction velocity of action potentials along axons in the alveus of the rat hippocampal CA1 region

Like neurons and astrocytes, oligodendrocytes have a variety of neurotransmitter receptors and ion channels. However, except for facilitating the rapid conduction of action potentials by forming myelin and buffering extracellular K(+), little is known about the direct involvement of oligodendrocytes in neuronal activities. To investigate their physiological roles, we focused on oligodendrocytes in the alveus of the rat hippocampal CA1 region. These cells were found to respond to exogenously applied glutamate by depolarization through N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors. Electrical stimulation of the border between the alveus and stratum oriens evoked inward currents through several routes involving glutamate receptors and inward rectifier K(+) channels. Moreover, electrical stimulation resembling in vivo activity evoked long-lasting depolarization. To examine the modulatory effects of oligodendrocytes on neuronal activities, we performed dual, whole-cell recording on CA1 pyramidal neurons and oligodendrocytes. Direct depolarization of oligodendrocytes shortened the latencies of action potentials evoked by antidromic stimulation. These results indicate that oligodendrocytes increase the conduction velocity of action potentials by a mechanism additional to saltatory conduction, and that they have active roles in information processing in the brain.