血小板激活因子对大鼠海马脑片CA1区LTP的作用

目的:为了探讨血小板激活因子(platelet-activating factor,PAF)对大鼠海马脑片CA1区的长时程增强效应(long-term potentiation,LTP)的影响.方法:应用离体脑片电生理记录技术,记录大鼠海马CA1区的兴奋性突触后电位EPSP,研究了PAF对大鼠海马脑片CA1区的突触传递和可塑性的影响.结果:小剂量(1μmol/L)PAF可诱发大鼠海马CA1区LTP的产生;大剂量(10～50μmol/L)PAF不能诱发大鼠海马CA1区LTP的产生,且不能阻止高频电刺激(HFS,100 Hz,1 000 ms×2,每隔20 s给予)Schffer侧支引起的大鼠海马脑片CA1区LTP的形成和维持.大剂量PAF对海马CA1区基础EPSP没有影响.PAF受体拮抗剂银杏苦内酯(ginkgolide B,GB)可拮抗小剂量PAF诱发大鼠海马CA1区LTP的产生.结论:大剂量PAF具有神经毒性,可能是通过抑制海马CA1区的LTP的形成而参与艾滋病痴呆(HIV-1 associated dementia,HAD)的形成机制.     

皮质酮对大鼠海马脑片CA1区长时程增强效应的影响

目的：探讨糖皮质激素对海马神经突触可塑性的影响。方法：高浓度（10^-5mol/L)皮质酮直接作用于大鼠海马脑片,记录CA1区LTP）。结果：海马脑片CA1区LTP的形成受到抑制。结论：应激时过量糖皮质激素会直接影响海马神经突触可塑性。     

锂对铅引起的大鼠海马CA1区长时程增强效应（LTP）损伤的修复作用

应用离体脑片记录技术,记录大鼠海马CA1区的兴奋性突触后电位(EPSPs),研究了锂对铅引起的大鼠海马CA1区长时程增强效应(long-termpotentiation,LTP)损伤的修复作用。结果表明:对照组大鼠海马CA1区LTP幅度为194.42±14.05%(n=10);铅处理组LTP的幅度为147.06±9.55%(n=13);而锂加铅处理组LTP的幅度为193.45±14.91%(n=15)。与对照组相比,铅处理组LTP的幅度降低了47.36%,而锂几乎完全修复了铅对大鼠海马CA1区LTP幅度的损伤。锂和铅处理后对大鼠海马CA1区的双脉冲易化(paired-pulsefacilica-tion,PPF)都有一定的抑制作用,在脉冲间隔为50ms时,这种抑制效应最大:对照组为155.58±6.35%(n=7);铅暴露组为150.26±13.74%(n=8);锂加铅处理组为140.59±15.42%(n=8)。结果表明:锂对铅引起大鼠海马CA1区LTP的损伤有一定的修复作用。     

大鼠海马CA1区β受体参与长时程增强和空间学习

在离体海马脑片上, 激活CA1区β肾上腺素能受体(β受体)易化这一区域突触传递的长时程增强(LTP). 然而, 在体情况下, CA1区β受体是否参与LTP的调控, 是否参与海马依赖性的学习和记忆, 尚无实验证据. 为此, 观察了β受体激动剂异丙肾上腺素或拮抗剂心得安对在体CA1区LTP的调控作用以及对大鼠在Morris水迷宫中的空间学习的影响. 正常情况下对突触强度仅有微小调制作用的10 Hz的θ节律刺激(每串150个脉冲, 1串), 在CA1区局部给予L-异丙肾上腺素后, 显著地诱导出LTP, 这一效应被DL-心得安所阻断; 相反, 正常情况下对突触强度有显著调制作用的5 Hz的θ节律刺激(每串150个脉冲, 3串), 在CA1区局部给予DL-心得安后, 诱导出的LTP显著地被压抑. 相应地, 训练前20 min在CA1区注射DL-心得安, 大鼠在水迷宫中的学习速度显著地慢于对照组大鼠, 训练后24 h的空间记忆保持亦相应较差. 以上结果表明, β受体参与海马CA1区的突触可塑性, 且对空间学习重要.     

钩藤对致痫大鼠海马脑片诱发场电位的影响

目的研究钩藤对癫痫模型海马脑片诱发场电位的影响。方法以毛果芸香碱致痫大鼠为实验对象,采用脑片旁滴注给药,用细胞外玻璃微电极记录方法,观察钩藤对癫痫模型离体海马脑片CA1区锥体细胞诱发群锋电位（populationspike,PS）的影响。结果给予钩藤后使致痫大鼠海马脑片PS幅度平均降低27.64％,平均8.71min恢复(n=14,P<0.01)。结论钩藤能降低致痫大鼠海马脑片CA1区顺向诱发PS幅度,提示钩藤对中枢神经系统的突触传递过程有明显的抑制效应,具有抗癫痫作用。     

Omega-3鱼油对铅暴露大鼠海马齿状回长时程增强损伤的保护作用(英文)

本文旨在探讨每天灌胃omega-3鱼油对慢性铅暴露(0.2%醋酸铅)导致的大鼠海马齿状回(dentate gyrus,DG)区突触可塑性损伤有无保护作用。将新生Wistar大鼠分为4组:正常对照组、铅组、正常+鱼油组、铅+鱼油组,染铅方式为饮用0.2%醋酸铅水,鱼油按0.4mL/100g体重采用灌胃方式给药,至大鼠80~90d时,4组大鼠进行海马DG区的场电位记录,记录兴奋性突触后电位(excitatory postsynaptic potential,EPSP)、群峰电位(population spike,PS)的长时程增强(long-term potentiation,LTP)。结果显示:出生后的铅暴露损伤了大鼠海马DG区的LTP;鱼油对正常对照组的LTP无显著影响,而对染铅大鼠LTP的损伤有明显的修复作用。以上结果提示omega-3鱼油可能对慢性铅暴露导致的LTP损害具有一定的保护作用。     

雷帕霉素对淀粉样β蛋白所致大鼠工作记忆和突触可塑性损伤的作用观察

目的:观察雷帕霉素对淀粉样β蛋白(Aβ1-42)所致大鼠工作记忆和突触可塑性损伤的影响。方法:SD大鼠(n=44)双侧海马注射Aβ1-42建立AD模型,雷帕霉素预处理后,进行Y-迷宫行为学实验和在体海马场电位实验,分别记录大鼠在Y-迷宫中的正确交替反应率和海马长时程增强(LTP)。结果:1与对照组相比,海马单独注射Aβ1-42可导致大鼠Y迷宫试验中工作记忆明显下降;2单独注射雷帕霉素不影响大鼠的工作记忆,但雷帕霉素预处理可有效逆转Aβ1-42引起的工作记忆损伤;3单独注射Aβ1-42明显压抑了大鼠在体海马CA1区突触传递的LTP效应;4雷帕霉素预处理有效逆转了Aβ1-42引起的LTP压抑。结论:雷帕霉素可有效拮抗Aβ1-42所致的大鼠工作记忆和突触可塑性损害,提示其具有一定的神经保护作用。     

小鼠在体海马长时程增强记录技术

目的:建立记录小鼠在体海马"前穿通纤维-齿状回"(PP-DG)神经通路长时程增强(LTP)的方法.方法:动物麻醉后固定于立体定位仪上,参照立体定位参数将刺激电极插入至前穿通纤维,记录电极插入至DG颗粒细胞层,而后进行LTP的诱发和记录.结果:对各种实验条件优化后,成功记录了Balb/c小鼠海马PP-DG通路LTP.应用该方法对快速老化模型小鼠(SAM)的快速老化亚系SAMP8和抗快速老化亚系SAMRl海马神经突触可塑性进行考察,结果表明在体海马LTP与脑片LTP和行为学实验结果相符.结论:成功建立了小鼠在体海马PP-DG通路LTP的记录方法,可用于整体动物神经突触可塑性的评价.     

双电极绑定技术记录在体大鼠海马CA1区长时程增强

目的:探讨双电极绑定条件下记录大鼠在体海马CA1区长时程增强的可行性。方法:雄性Wistar大鼠乌拉坦麻醉;脑立体定位仪上埋置脑室导管;安装自制的刺激/记录绑定电极;引导基础性场兴奋性突触后电位(fEP-SP);强直刺激诱导长时程增强(LTP)。结果:绑定后的刺激和记录电极能可靠地引起海马CA1区fEPSP,fEPSP的出现率几乎100%;基础性fEPSP记录可保持长时间稳定;高频刺激成功诱导出LTP并维持达3h以上,诱导率约67%;双脉冲易化记录稳定、可靠;脑室注射β淀粉样蛋白(Aβ)对LTP显示出明显的压抑作用。结论:采用双电极绑定技术进行在体海马LTP记录简便易行、节省资源、引导fEPSP和诱导LTP的成功率较高,有望成为一项重要的研究学习和记忆机制的电生理辅助手段。     

应激诱发的海马神经元突触增强参与大鼠的新环境学习

本文旨在研究应激对海马新环境空间学习记忆的损伤作用机制.在大鼠海马CA1区埋植电极,刺激schaffer侧枝记录CA1区树突层的兴奋性突触后场电位(field excitatory postsynaptic potential,fEPSP),探索应激对火鼠新环境空间学习的突触可塑性的影响.同时研究了再次新环境空间学习时...     

Modulation of ATP-induced LTP by cannabinoid receptors in rat hippocampus

Cannabinoids exert powerful action on various forms of synaptic plasticity. These retrograde messengers modulate GABA and glutamate release from presynaptic terminals by acting on presynaptic CB1 receptors. In particular, they inhibit long-term potentiation (LTP) elicited by electrical stimulation of excitatory pathways in rat hippocampus. Recently, LTP of the field excitatory postsynaptic potential (fEPSP) induced by exogenous ATP has been thoroughly explored. The present study demonstrates that cannabinoids inhibit ATP-induced LTP in hippocampal slices of rat. Administration of 10 μM of ATP led to strong inhibition of fEPSPs in CA1/CA3 hippocampal synapses. Within 40 min after ATP removal from bath solution, robust LTP was observed (fEPSP amplitude comprised 130.1 ± 3.8% of control, n = 10). This LTP never appeared when ATP was applied in addition to cannabinoid receptor agonist WIN55,212-2 (100 nM). Selective CB1 receptor antagonist, AM251 (500 nM), completely abolished this effect of WIN55,212-2. Our data indicate that like canonical LTP elicited by electrical stimulation, ATP-induced LTP is under control of CB1 receptors.

Electronic supplementary material

The online version of this article (doi:10.1007/s11302-012-9296-5) contains supplementary material, which is available to authorized users.     

Inhibition of post-synaptic Kv7/KCNQ/M channels facilitates long-term potentiation in the hippocampus

Activation of muscarinic acetylcholine receptors (mAChR) facilitates the induction of synaptic plasticity and enhances cognitive function. In the hippocampus, M(1) mAChR on CA1 pyramidal cells inhibit both small conductance Ca(2+)-activated KCa2 potassium channels and voltage-activated Kv7 potassium channels. Inhibition of KCa2 channels facilitates long-term potentiation (LTP) by enhancing Ca(2+)calcium influx through postsynaptic NMDA receptors (NMDAR). Inhibition of Kv7 channels is also reported to facilitate LTP but the mechanism of action is unclear. Here, we show that inhibition of Kv7 channels with XE-991 facilitated LTP induced by theta burst pairing at Schaffer collateral commissural synapses in rat hippocampal slices. Similarly, negating Kv7 channel conductance using dynamic clamp methodologies also facilitated LTP. Negation of Kv7 channels by XE-991 or dynamic clamp did not enhance synaptic NMDAR activation in response to theta burst synaptic stimulation. Instead, Kv7 channel inhibition increased the amplitude and duration of the after-depolarisation following a burst of action potentials. Furthermore, the effects of XE-991 were reversed by re-introducing a Kv7-like conductance with dynamic clamp. These data reveal that Kv7 channel inhibition promotes NMDAR opening during LTP induction by enhancing depolarisation during and after bursts of postsynaptic action potentials. Thus, during the induction of LTP M(1) mAChRs enhance NMDAR opening by two distinct mechanisms namely inhibition of KCa2 and Kv7 channels.     

Enhanced anandamide degradation is associated with neuronal apoptosis induced by the HIV-1 coat glycoprotein gp120 in the rat neocortex

Human immunodeficiency virus type-1 coat glycoprotein gp120 causes delayed apoptosis in rat brain neocortex. Here, we investigated the possible role of the endocannabinoid system in this process. It is shown that gp120 causes a time-dependent increase in the activity and immunoreactivity of the anandamide (AEA)-hydrolyzing enzyme fatty acid amide hydrolase (FAAH), paralleled by increased activity of the AEA membrane transporter and decreased endogenous levels of AEA. The AEA-synthesizing phospholipase D and the AEA-binding receptors were not affected by gp120. None of the changes induced by gp120 in the cortex were induced by bovine serum albumin, nor were they observed in the hippocampus of the same animals. Also, the activity of 5-lipoxygenase, which generates AEA derivatives able to inhibit FAAH, decreased down to approximately 25% of the control activity upon gp120 treatment, due to reduced protein level ( approximately 45%). In addition, the FAAH inhibitor methyl-arachidonoyl fluorophosphonate significantly reduced gp120-induced apoptosis in rat brain neocortex, whereas selective blockers of AEA membrane transporter or of AEA-binding receptors were ineffective. Taken together, these results suggest that gp120, by activating FAAH, decreases endogenous levels of AEA, and the latter effect seems instrumental in the execution of delayed neuronal apoptosis in the brain neocortex of rats.     

Mode of action for linear peptide inhibitors of HIV-1 gp120 interactions

The linear peptide 12p1 (RINNIPWSEAMM) was previously isolated from a phage display library and was found to inhibit interaction of HIV-1 gp120 with both CD4 and a CCR5 surrogate, mAb 17b [Ferrer, M., and Harrison, S. (1999) J. Virol. 73, 5795-5802]. In this work, we investigated the mechanism that leads to this dual inhibition of gp120 binding. We found that there is a direct interaction of 12p1 with gp120, which occurs with a binding stoichiometry of 1:1. The peptide inhibits binding of monomeric YU2 gp120 to both sCD4 and 17b at IC(50) values of 1.1 and 1.6 microM, respectively. The 12p1 peptide also inhibited the binding of these ligands to trimeric envelope glycoproteins, blocked the binding of gp120 to the native coreceptor CCR5, and specifically inhibited HIV-1 infection of target cells in vitro. Analyses of sCD4 saturation of monomeric gp120 in the presence or absence of a fixed concentration of peptide suggest that 12p1 suppression of CD4 binding to gp120 is due to allosteric inhibitory effects rather than competitive inhibition of CD4 binding. Using a panel of gp120 mutants that exhibit weakened inhibition by 12p1, the putative binding site of the peptide was mapped to a region immediately adjacent to, but distinguishable from, the CD4 binding footprint. In the case of the peptide, the effects of single-12p1 residue substitutions and various peptide truncations indicate that the side chain of Trp7 and other structural elements of 12p1 are critical for gp120 binding or efficient inhibition of binding of a ligand to gp120. Finally, 12p1 was unable to inhibit binding of sCD4 to a gp120 mutant that is believed to resemble the CD4-induced conformation of gp120. These results suggest that 12p1 preferentially binds gp120 prior to engagement of CD4; binding of the peptide to gp120 limits the interaction with ligands (CD4 and CCR5) that are generally crucial for viral entry. More importantly, these results indicate that 12p1 binds to a unique site that may prove to be a prototypic target for novel CD4-gp120 inhibitors.     

Antiserum Against S-100 Protein Prevents Long Term Potentiation Through a cAMP-Related Mechanism

Long term potentiation (LTP) was induced in the CA1 region of rat hippocampal slices by tetanization of the Schaffer collaterals. Local pretreatment of CA1 with serum of rabbits immunized against S-100 prevented the potentiation. However, treatment of the slices with a membrane permeant cAMP analogue, such as 8-Br-cAMP, could protect against the blocking effect of anti S-100 serum. We suggest that in the rat endogenous S-100_b is involved in transduction mechanisms during LTP induction, via its ability to stimulate adenylate cyclase. Possible mechanisms of this action are discussed.     

A dynamic target-based pharmacophoric model mapping the CD4 binding site on HIV-1 gp120 to identify new inhibitors of gp120–CD4 protein–protein interactions

A dynamic target-based pharmacophoric model mapping the CD4 binding site on HIV-1 gp120 was built and used to identify new hits able to inhibit gp120–CD4 protein–protein interactions. Two compounds showed micromolar inhibition of HIV-1 replication in cells attributable to an interference with the entry step of infection, by direct interaction with gp120. Inactivity of compounds toward a M475I strain suggested specific contacts with the Phe43 cavity of gp120.     

Inhibition of hippocampal LTP by ginkgolide B is mediated by its blocking action on PAF rather than glycine receptors

Platelet-activating factor (PAF), a biologically active lipid (1-O-alkyl-2-acetyl-sn-glycero-3-phosphoholine), is identified in different regions of brain, including hippocampus. Specific PAF-activated receptors (PAFRs) are expressed in corresponding brain areas. PAF has been proposed to be a retrograde messenger of long-term potentiation (LTP): the antagonist of PAFRs, ginkgolide B (or BN52021) prevents induction of LTP. Recently it has been found that ginkgolide B is also an efficient blocker of the glycine receptor (GlyR) operated chloride channels (IC(50)=270+/-10 nM in hippocampal pyramidal neurons). The question is as follows: is the alteration of LTP by BN52021 due to the PAF antagonism or to the inhibition of glycine-gated chloride channels? We have studied the effects of ginkgolides B and J on LTP induced in the CA1 area of rat hippocampus. Ginkgolide J which is the weakest blocker of PAFR (IC(50)=54 microM, as compared to IC(50)=2.5 microM for ginkgolide B) inhibits GlyR-operated channels with IC(50)=2.0 microM. This assures a convenient concentration window which allows to inhibit GlyR-operated channels without affecting PAFRs. An amount of 5 microM of ginkgolide J did not prevent the induction of LTP, while ginkgolide B (5 microM) completely inhibited this phenomenon. The effect of ginkgolide B on LTP did not alter considerably if GlyRs were blocked by strychnine (2 microM). Strychnine itself had no significant effect on the induction of LTP. Both ginkgolides and strychnine significantly facilitated short-term potentiation (STP). Our data support a hypothesis according to which ginkgolides affect LTP by inhibiting PAFRs.     

Clonidine Suppresses the Induction of Long-Term Potentiation by Inhibiting HCN Channels at the Schaffer Collateral–CA1 Synapse in Anesthetized Adult Rats

Activation of alpha2-adrenoceptors inhibits long-term potentiation and long-term depression in many brain regions. However, effectiveness and mechanism of alpha2-adrenoceptors for synaptic plasticity at the Schaffer collateral–CA1 synapses in rat in vivo is unclear. In the present study, we investigated the effects of alpha2-adrenoceptors agonist clonidine on high-frequency stimulation (HFS)-induced long-term potentiation (LTP) and paired-pulse facilitation (PPF) at the Schaffer collateral–CA1 synapse of rat hippocampus in vivo. Clonidine (0.05, 0.1 mg/kg, ip) inhibited synaptic plasticity in a dose-dependent manner, accompanying with the decreasing of aortic pressure and heart rate (HR) in anesthetized rats. Clonidine (1.25, 2.5 μg/kg, icv, 10 min before HFS) also dose-dependently inhibited synaptic plasticity, which had no remarkable effect on HR and aortic pressure. But, 20 min after HFS, administration of clonidine (2.5 μg/kg) had no effect on LTP. The inhibitory effect of clonidine (2.5 μg/kg) on LTP was completely reversed by yohimbine (18 μg/kg, icv) and ZD7288 (5 μg/kg, icv). Moreover, the inhibition was accompanied by a significant increase of the normalized PPF ratio. Furthermore, clonidine at 1 and 10 μM significantly decreased glutamate (Glu) content in the culture supernatants of hippocampal neurons, and yohimbine at 1 and 10 μM had no effect on Glu release, while it could reverse the inhibition of clonidine (1 and 10 μM) on Glu release. In conclusion, clonidine can suppress the induction of LTP at the Schaffer collateral–CA1 synapse, and the possible mechanism is that activation of presynaptic alpha2-adrenoceptors reduces the Glu release by inhibiting HCN channels.     

Curcumin Protects Microglia and Primary Rat Cortical Neurons against HIV-1 gp120-Mediated Inflammation and Apoptosis

Curcumin is a molecule found in turmeric root that has anti-inflammatory, antioxidant, and anti-tumor properties and has been widely used as both an herbal drug and a food additive to treat or prevent neurodegenerative diseases. To explore whether curcumin is able to ameliorate HIV-1-associated neurotoxicity, we treated a murine microglial cell line (N9) and primary rat cortical neurons with curcumin in the presence or absence of neurotoxic HIV-1 gp120 (V3 loop) protein. We found that HIV-1 gp120 profoundly induced N9 cells to produce reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1). HIV-1 gp120 also induced apoptosis of primary rat cortical neurons. Curcumin exerted a powerful inhibitory effect against HIV-1 gp120-induced neuronal damage, reducing the production of ROS, TNF-α and MCP-1 by N9 cells and inhibiting apoptosis of primary rat cortical neurons. Curcumin may exert its biological activities through inhibition of the delayed rectification and transient outward potassium (K⁺) current, as curcumin effectively reduced HIV-1 gp120-mediated elevation of the delayed rectification and transient outward K⁺ channel current in neurons. We conclude that HIV-1 gp120 increases ROS, TNF-α and MCP-1 production in microglia, and induces cortical neuron apoptosis by affecting the delayed rectification and transient outward K⁺ channel current. Curcumin reduces production of ROS and inflammatory mediators in HIV-1-gp120-stimulated microglia, and protects cortical neurons against HIV-1-mediated apoptosis, most likely through inhibition of HIV-1 gp120-induced elevation of the delayed rectification and transient outward K⁺ current.     

Effects of localized applications of L-glutamate on the population spike in the hippocampal slice preparation

L-Glutamate applied exclusively to the CA3 cell body region of the rat hippocampal slice resulted in long-term potentiation (LTP) of the CA1 population spike evoked by Schaffer collateral stimulation. The same localized glutamate application to the CA1 area caused a prolonged depression of the response. These observations are consistent with the possibility that LTP is at least partly presynaptic and that the depression is due to an effect of glutamate on the postsynaptic elements and/or the presynaptic terminals.