NMDA受体介导的eEPSC在皮质发育障碍动物模型海马CA1区的改变

目的：研究皮质发育障碍（DCD）大鼠模型海马CA1区N-甲基-D-门冬氨酸（NMDA）受体及α-氨基-3-羧基5甲基异恶唑-4-丙酸（AmPA）受体介导的兴奋性突触后电流（eEPSC）的变化，探讨DCD大鼠模型的致痫机制。方法：选取出生10～20dDCD幼鼠模型和正常对照组，应用可视法脑片膜片钳记录方法，记录大鼠海马CA1区锥体神经元的NMDA受体及AmPA受体介导的eEPSC幅度及衰减时间常数。结果：DCD模型组与正常对照组相比，NMDA受体介导的eEPSC的幅度有明显增高r（119．54±10．97）pAVS（83．69±10．23）pA；P〈0．053；衰减时间常数明显延长[（154．59±3．92）VS（117．18±4．04）；P〈0．05]。而AmPA受体介导的eEPSC的幅度[（139．99±23．41）pAVS（135．50±26．44）pA；P〉0．05]及衰减时间常数[（47．23±2．28）VS（48．68±2．20）；P〉0．053无明显改变。结论：NMDA受体介导的异常突触后反应在DCD的致痫机制方面起到重要的作用。     

皮质发育障碍大鼠海马神经元的体视学方法定量研究

目的　用体视学方法计数比较X射线制作的大脑皮质发育障碍（DCDs）模型大鼠海马神经元数量变化和测量海马体积变化。 方法　选择2月龄正常SD大鼠和DCDs模型鼠各5 只,取脑后石蜡包埋、连续冠状切片。根据均匀系统随机抽样原则,从含海马结构的切片中随机抽取一组切片,组织化学染色,在体视学设备下计数大鼠海马CA1、CA3和DG区的神经元数目和测量海马体积。 结果　正常大鼠单侧海马CA1、CA3和DG区的神经元的数目分别是（8.35×104±1.44×104）、（8.23×104±1.60×104）和（1.43×105±2.24×104）,DCDs模型大鼠单侧海马CA1、CA3和DG区的神经元的数目分别是（3.70×104±　1.96×104）、（3.57×104±1.47×104）和（6.86×104±4.85×104）;正常大鼠和DCDs模型鼠单侧海马的体积分别是(14.18±1.52)mm3和(8.49±3.41)mm3。DCDs大鼠海马结构各亚区的神经元数量和海马体积均较正常鼠明显减小（P＜0.05）。 结论　X射线制作的DCDs模型鼠海马CA1、CA3和DG的神经元数目和海马体积都较正常大鼠减少。     

大脑皮质发育障碍模型病理学与影像学研究

目的：探讨应用X射线构建的大脑皮质发育障碍（DCD）模型鼠病理学与影像学特点。方法：应用直线加速器以175cGy剂量照射孕17dSD母鼠，待仔鼠满56d时行鼠脑磁共振扫描后处死，取脑进行组织病理学研究。结果：DCD仔鼠较对照组大鼠大脑组织重量减轻，体积显著缩小，大脑皮层变薄，厚度较小，双侧侧脑室、第三脑室、第四脑室明显扩大；光镜下见大脑皮层结构紊乱，其内可见结节，海马结构紊乱，海马内结节明显。DCD仔鼠头颅MRI特点：脑体积略小，皮层厚度变薄，双侧侧脑室、第三脑室、第四脑室明显扩大，胼胝体变小伴有缺如，四叠体明显暴露，小脑体积变大。结论：DCD从模型鼠病理学与影像学特征可以反映X射线是构建大脑皮质发育障碍的有效方法，影像学是评估DCD造模是否成功的可供选择的一种手段。     

学习记忆与一氧化氮及长时程增强效应

长时程增强 (Long termPotentiation ,LTP)现象的发现及其机理的探讨 ,以及一氧化氮 (NitricOx ide,NO)作为一种特殊的神经递质分子的深入研究 ,使学习记忆的机制研究提高到了细胞和分子水平。但有关LTP ,NO和学习记忆的明确关系尚存在不少争议。本文就近年来三者的研究进展作一简要综述     

锌缺乏对小鼠海马长时程增强的影响

目的探讨锌缺乏对小鼠海马区域锌离子含量以及长时程增强(LTP)的影响。方法 3周龄CD-1小鼠饲以低锌饲料(0.85mg/kg)和去离子水5周进行实验。应用金属自显影技术(AMG)检测低锌饲料喂养对小鼠海马游离锌离子含量的影响;在小鼠海马齿状回的苔藓纤维层插入刺激电极,在CA3区锥体细胞层插入记录电极,记录高频刺激后海马苔藓纤维CA3区引起的峰电位(PS)和兴奋性突触后电位(f-EPSP)的变化,分析锌缺乏对小鼠海马LTP形成的影响。结果 AMG结果显示锌缺乏小鼠海马CA1,CA3和齿状回区域的锌离子含量明显降低(P<0.05-0.01);电生理检测结果表明锌缺乏小鼠在高频刺激后海马苔藓纤维的PS和f-EPSP均显著下降(P<0.01),提示锌缺乏抑制小鼠海马长时程增强的形成。结论锌缺乏使小鼠海马游离锌离子含量下降,参与对海马长时程增强形成的抑制。     

外源性硫化氢对海洛因依赖大鼠海马长时程增强的影响

目的:观察外源性H2S供体NaHS对海洛因依赖大鼠学习记忆能力及海马LTP的影响。方法:SD大鼠随机分成3组:正常对照组、heroin组、heroin+NaHS组。先通过跳台实验检测大鼠学习记忆能力,然后记录高频刺激(HFS)前后在体海马CA1区群体峰电位(PS)变化,诱导长时程增强(LTP)的产生,最后通过Nissl染色观察海马神经元的损伤情况。结果:与对照组比较,heroin组和heroin+NaHS组学习记忆成绩均降低(P<0.05),PS幅值变化率减小(P<0.01),且形态学观察可见海马神经元损伤;与heroin组比较,heroin+NaHS组学习记忆成绩提高(P<0.05),PS幅值变化率增大(P<0.01),海马神经元损伤较轻。结论:(1)海洛因依赖导致大鼠海马神经元损伤,抑制海马CA1区LTP的产生,从而降低正常学习记忆能力;(2)外源性H2S可减轻海洛因依赖对大鼠海马神经元的损伤,易化海马CA1区LTP的产生,改善海洛因依赖导致的正常学习记忆能力的降低。     

皮质发育障碍模型鼠脑皮质形态学和致痫机制研究

目的：观察皮质发育障碍（DCDs）大鼠脑皮质形态学及海马苔藓纤维发芽的情况，探讨其与癫痫发生的关系。方法：建立DCDs动物模型，观察其行为、EEG改变，采用HE染色、Nissl染色和Timm’s硫化银组织化学染色，肉眼和光镜下观察大鼠脑皮质形态变化，评估海马苔藓纤维发芽情况，各组数据取苔藓纤维发芽评分，采用非参数秩和Kruskal-Wallis H检验，组间两两比较用Nemenyi法。结果：①正常对照组和母鼠组大鼠无抽搐发作，F1代组少数自发性癫痫发作，大多表现活动增多、兴奋躁动、搔抓和“洗脸样活动”频繁。②大多数皮层电极EEG示小波幅节律为主，无典型的尖波、棘波、尖慢波、棘慢综合波发放。③F1代鼠脑皮质结构紊乱，双侧海马CA3区均有苔藓纤维发芽（P〈0．05），而正常对照组和假手术组脑结构未见异常。结论：脑皮质和海马的结构异常及海马CA3区苔藓纤维发芽可能是DCDs导致癫痫发生的重要机制。     

一氧化氮对高频电刺激后海马长时程增强和c-fos表达的影响

本研究采用海马离体脑片胞外记录电生理技术和免疫组化技术,观察了一氧化氮对高频电刺激后海马ＣＡ１ 区长时程增强和ｃ ｆｏｓ表达的影响。结果表明：一氧化氮合酶的抑制剂ＮＧ 硝基精氨酸和一氧化氮耗竭剂血红蛋白显著抑制了长时程增强的产生,而在同一海马脑片上所表达的ｃ ｆｏｓ蛋白样免疫反应未见明显变化。提示一氧化氮参与了长时程增强的过程,但不参与高频电刺激后ｃ ｆｏｓ的表达。     

海马长时程增强形成机制的研究近况

长时程增强现象是学习和记忆的细胞机制，它的形成是突触前后机制共同参与的结果。海马是神经系统参与第一级记忆的关键部位。突触前的递质释放和突触后的Ｃａ２＋通道、蛋白激酶，尤其是逆行性信使与海马长时程增强的关系密切     

Aβ25-35伤害大鼠空间学习记忆和在体海马长时程增强的联合研究

目的:探讨海马内注射β-amyloid protein 25-35(Aβ25-35)所致Alzheizer’s病(AD)模型大鼠空间学习记忆功能障碍的海马突触可塑性长时程增强(LTP)机制,为联合开展AD动物行为学和在体电生理学研究提供实验证据。方法:在脑立体定位仪上给予大鼠双侧海马分别注射4 nmol/L Aβ25-35或等体积生理盐水每侧2μl,手术后恢复2周,每只大鼠依次进行行为学和电生理两部分实验。首先,利用Morris水迷宫进行空间学习、记忆功能测试;之后,进行在体海马CA1区场兴奋性突触后电位(fEPSP)引导记录实验,观察突触可塑性指标长时程增强(LTP)的改变。结果:与对照组相比,海马内注射Aβ25-35大鼠的空间学习记忆功能和在体海马突触可塑性LTP均有改变,其中:逃避潜伏期和逃避距离明显增加(P<0.01);目标象限内游泳时间和距离明显缩短(P<0.01);在体海马LTP幅度显著降低(P<0.01)。结论:海马内注射Aβ25-35可导致大鼠空间学习记忆功能障碍;联合实验中Aβ25-35同样可引起在体海马LTP改变。提示同批动物先后进行行为学和电生理学测试的方法是可行的,行为学实验不会影响后续LTP的实验结果。因此,本实验为行为学改变后进行在体LTP机制探讨提供了实验依据,为有效开展行为学和电生理学实验提供了思路。     

Chronic brain inflammation impairs two forms of long-term potentiation in the rat hippocampal CA1 area

Neuroinflammation plays an important role in the progression of Alzheimer's disease (AD) and is characterized by the presence of activated microglia. We investigated whether chronic neuroinflammation affects the induction of N-methyl-d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) and NMDAR-independent LTP which is expressed by voltage-dependent calcium channel (VDCC). Chronic neuroinflammation was induced by administration of lipopolysaccharide (LPS) (28 days, 0.35 μg/h) to the fourth ventricle. The Morris water maze test was conducted to measure the memory impairment and then excitatory postsynaptic potentials were recorded extracelluarly from stratum radiatum in the rat hippocampal CA1 area to examine the changes in synaptic plasticity induced by LPS infusion. Chronic administration of LPS induced remarkable memory impairment. The field recording experiments revealed that the induction of both NMDAR-dependent LTP and NMDAR-independent LTP were impaired in the hippocampal Schaffer collateral-CA1 synapse in animals chronically infused with LPS. The present results show that chronic neuroinflammation can lead to the impaired spatial memory and attenuation of VDCC-dependent LTP as well as NMDAR-dependent LTP. The attenuation of synaptic plasticity may be caused by the impairment of both NMDAR and L-type Ca²⁺ via elevated levels of inflammatory proteins, which may underlie aspects of dementia.     

Vagus nerve stimulation potentiates hippocampal LTP in freely-moving rats

Previous studies have demonstrated that electrical stimulation of the vagus nerve (VNS) delivered at a moderate intensity following a learning experience enhances memory in laboratory rats and human subjects, while VNS at lower or higher intensities has little or no effect. This finding suggests that VNS may affect memory processes by modulating neural plasticity in brain structures associated with memory storage such as the hippocampus. To test this hypothesis, the present study investigated the modulatory effect of VNS on the development of long-term potentiation (LTP) in the dentate gyrus of freely-moving rats. Rats receiving 0.4 mA VNS showed enhanced potentiation of the population spike amplitude for at least 24 h after tetanus relative to the sham-stimulation group. In contrast, no such effect was observed with 0.2 mA VNS. Stimulation at 0.8 mA had a short-term effect and tended to enhance early LTP, but to a lesser extent than did 0.4 mA. The 0.4 mA stimulation was the same intensity that was previously shown to enhance retention performance in an inhibitory avoidance task. These findings suggest that the neural mechanisms underlying the mnemonic effect of VNS may involve modulating synaptic plasticity in the hippocampus. These data also suggest that neural activity in the vagus nerve, occurring as a result of changes in peripheral state, is an important mechanism by which emotional experiences and arousal can enhance the storage of memories of those experiences.     

Ghrelin induced memory facilitation implicates nitric oxide synthase activation and decrease in the threshold to promote LTP in hippocampal dentate gyrus

Although the hypothalamus has been long considered the main ghrelin (Ghr) target organ mediating orexigenic effects, recently it has been shown that in-vivo Ghr hippocampus administration improves learning and memory in the inhibitory avoidance paradigm. However, the possible mechanisms underlying this memory facilitation effect have not been clarified. Given that the biochemical memory cascade into the hippocampus involves nitric oxide (NO) synthesis via NO synthase (NOS) activation, we investigated 1) if Ghr administration modulated NOS activity in the hippocampus; and 2) if hippocampal NOS inhibition influenced Ghr-induced memory facilitation, using a behavioral paradigm, biochemical determinations and an electrophysiological model. Our results showed that intra-hippocampal Ghr administration increased the NOS activity in a dose dependent manner, and reduced the threshold for LTP generation in dentate gyrus of rat hippocampus. Moreover, pre-administration of NG-nitro-l-arginine (l-NOArg) in the hippocampus partially prevented the Ghr-induced memory improvement, abolished the increase in NOS activity, and prevented the decreased threshold to generate LTP induced by Ghr. These findings suggest that activation of the NOS/NO pathway in hippocampus participates in the effects of Ghr on memory consolidation and is related with plastic properties of the hippocampal three-synaptic loop.     

Neonatal hyperthyroidism disrupts hippocampal LTP and spatial learning

Summary Excess thyroid hormone at an early stage of development produces marked neurochemical and morphological alterations in the rat hippocampal formation. In order to better understand the functional significance of these changes, we tested adult rats treated neonatally with triiodothyronine (T3), and their control litter mates, in a spatial learning task and for the induction of longterm potentiation (LTP) in the dentate gyrus (DG) of the hippocampal formation. The T3-treated rats were significantly impaired in their performance on the spatial task in comparison to their matched controls. Similarly, the efficacy of LTP induction was significantly attenuated in the T3-treated animals. Further, a significant correlation was obtained between LTP induction and performance on the spatial learning task. Thus, a brief neonatal excess of thyroid hormone produces impairments in spatial learning along with decreases in LTP, long held as a model of learning and memory. This relationship provides a unique opportunity to study associations between behavioral, physiological, pharmacological and morphological processes intimately associated with the hippocampal formation     

High-frequency magnetic stimulation induces long-term potentiation in rat hippocampal slices

Recent reports indicate that the exposure of brain tissues to transcranial magnetic stimulation induces persistent changes in neuronal activity and influences hippocampal synaptic plasticity. However, the modulation of synaptic efficiency by magnetic stimulation in vitro is still unclear. In the present study, we investigated whether high-frequency magnetic stimulation (HFMS) can induce long-term potentiation (LTP) in rat hippocampal slices in vitro. During baseline recording and after HFMS, field excitatory postsynaptic potentials (fEPSPs) were recorded within the CA1 stratum radiatum in response to electrical stimulation of the Schaffer collateral inputs. For LTP induction, HFMS was delivered through a circular coil positioned closely above the slices using two different paradigms (A: 10 trains of 20 pulses at 100 Hz with 1 s intervals, 5 repetitions with 10 s intervals; B: 3 trains of 100 pulses at 100 Hz with 20 s intervals). The intensity of the magnetic stimulus was adjusted to 60–75 A/μs. After application of HFMS, electrically evoked CA1 fEPSPs were enhanced showing significant levels of LTP by both paradigms (A: 142 ± 9% of baseline, n = 6; B: 129 ± 7%, n = 8). Furthermore, HFMS-induced LTP induced by paradigm A was prevented by the presence of the selective N-methyl-d-aspartate receptor (NMDAR) blocker D-AP5 (50 μM) in the bath solution (95 ± 6% of the baseline, n = 6; p < 0.01 compared to control condition without D-AP5). Further, the lack of changes in paired-pulse ratio and the afferent fiber volleys exclude presynaptic involvement in HFMS-induced LTP. In summary, we have demonstrated that HFMS can induce NMDAR-dependent LTP in the CA1 region in vitro.     

A decrease in firing threshold observed after induction of the EPSP-spike (E-S) component of long-term potentiation in rat hippocampal slices

Summary Two components of long-term potentiation (LTP) are distinguished with extracellular recording electrodes: a synaptic and an EPSP-Spike (E-S) component. The latter consists of the enhancement produced in the population spike amplitude in excess of that predicted by EPSP potentiation alone. The experiments carried out in this study were designed to investigate intracellular correlates of E-S potentiation and to examine the hypothesis that an increased postsynaptic excitability underlies E-S potentiation. CA1 pyramidal neurons were synaptically activated from stratum radiatum. LTP, defined as a stable increase in the probability of firing to afferent stimulation, was found to be related to a decrease in the intracellular PSP peak amplitude and slope required to fire the cells at a probability of 0.5. These changes were accompanied by a decrease in threshold to direct activation. No significant changes in input resistance or resting potential were recorded. These excitability changes were only observed in cells displaying LTP; they were not related to the potentiation of the synaptic component (PSP amplitude). Our results support the hypothesis that different mechanisms underlie the two components of LTP, and that a reduction in threshold for neuronal discharge accompanies tetanus-induced E-S potentiation. It is suggested that an increase in the ratio of synaptically evoked excitation/inhibition and a reduction in tonic synaptic inhibition through GA-BA_A channels contribute to E-S potentiation.     

Electroacupuncture restores learning and memory impairment induced by both diabetes mellitus and cerebral ischemia in rats

Previous investigations have demonstrated that electroacupunctural stimulation can ameliorate primary and secondary symptoms such as peripheral neuropathy and diabetic encephalopathy in diabetic rats. In this study, we investigated whether electroacupuncture could improve learning and memory which was typically impaired in diabetic rats with cerebral ischemia. Furthermore, we investigated the mechanisms underlying its effects using passive avoidance test, active avoidance test, Morris water maze and electrophysiology. Electroacupuncture increased the step-down latency in passive avoidance test and accurate rate in active avoidance test, decreased the escape latency in Morris water maze. After electroacupuncture treatment, the long-term potentiation (LTP) impaired by both diabetes and cerebral ischemia was restored significantly. These results suggest that electroacupuncture can ameliorate learning and memory capacity impaired by hyperglycemia and ischemia. LTP plays a very important role in this beneficial effect.     

Brief exposure to the G-protein activator NaF/AlCl3 induces prolonged enhancement of synaptic transmission in area CAl of rat hippocampal slices

Summary Rat hippocampal slices were exposed briefly (12–15 min) to AlF_4- (10 mmol/l NaF, 10 mol/l AlCl³). The effect on synaptic transmission in area CAl was measured using extracellular electrodes placed in the stratum pyramidale and stratum radiatum. During fluoride exposure, both spike and EPSP amplitude fell to very low levels. Upon washout, spike amplitude recovered beyond control values, and in half of the preparations a prolonged enhancement of spike amplitude (> 2 h) occurred. Similar modulation of EPSP slope indicated that these charges were primarily synpatic. If Al³⁺ was omitted from the F^--containing saline, enhancement of spike amplitude, when observed, was brief (20–30 min) and no enhancement of EPSP slope was seen. Omission of Ca²⁺ from the AlF_4--containing saline also abolished any long-lasting enhancement of synaptic transmission, though population spike amplitude in most slices showed a brief (20–30 min) stimulatory response. In preparations in which LTP had previously been saturated, synaptic transmission was not enhanced by exposure to AlF_4-. It is concluded that NaF/ACl₃ exposure induces an LTP-like process by G-protein activation, which involves recruitment of processes involved in LTP, possibly including an enhancement of Ca²⁺-influx.