同一学习中海马不同区的习得性长时程突触增强的形成

本研究探查大鼠分辨学习中海马齿状回(DG)和CA_3区突触效应的变化及其相互关系,以探讨同一学习中海马不同区突触可塑性变化的特点及其相互关系,进一步论证习得性长时程增强(LTP)是学习和记忆的神经基础。发现:(1)穿通纤维的单个刺激可在DG和CA_3同时记录到潜伏期、峰值和波形各异的群体峰电位(PS);在一定范围内PS随刺激强度的增加而增大,但DG的PS增大程度比CA_3的小;据此,检测刺激的强度应选在该范围内。(2)随着行为训练,DG和CA_3区的突触传递同时产生LTP,两者LTP的发展是显著正相关关系(P<0.01),PS峰值同时达到最高水平,且先于分辨反应达学会标准,首次表明在同一学习中大鼠海马的DG和CA_3的习得性LTP是同时产生的。本研究还表明,在慢性实验下同时记录和分析行为学习中海马两个区突触效应的变化及其相互关系是可能的,这给从神经环路角度研究学习和记忆的突触机制提供了有用的模型。     

去甲肾上腺素对习得性长时程突触增强的影响

在大鼠条件性饮水反应的建立和巩固过程中,在每天训练之前,通过预先与记录电极一起埋植在海马齿状回的注药管,微量注射去甲肾上腺素(NE),观察其对海马齿状回的习得性长时程突触增强的影响。结果表明:NE能增强突触效应;训练作业前注NE易化了习得性长时程突触增强的形成,但对其巩固无影响;同时相应地易化了动物条件反应的建立。提示NE参与海马齿状回的习得性长时程增强的形成。本文对其可能的作用机制进行了讨论。     

乳头体对海马齿状回习得性长时程突触增强的影响

用高频电脉冲刺激大鼠乳头体（ＭＢ）,可一过性抑制由刺激穿通纤维（ＰＰ）诱发的海马齿状回（ＤＧ）群体锋电位（ＰＳ）。训练作业前先刺激ＭＢ,导致ＤＧ的习得性长时程突触增强（ＬＤＬＴＰ）的形成显著延缓,相应地延缓了条件性饮水反应的建立。电刺激ＭＢ对ＰＰ─ＤＧＰＳ的这种抑制作用在训练所产生的ＰＳ增大达最高水平时显著减弱,刺激ＭＢ对ＬＤＬＴＰ的保持及相应地对条件反应的巩固没有明显影响。结果表明ＭＢ对ＤＧＬＤＬＴＰ的形成有抑制性调制作用。     

NMDA受体在海马习得性长时程突触增强形成中的作用

本文应用慢性埋植技术以电生理学结合行为学的方法,在大鼠条件性饮水反应的建立中,于每实验日训练开始前给海马CA_3区微量注射NMDA受体拮颃剂2-amino-5-phosphonovalerate(APV),观察它对海马CA_s区突触效应及与之相关的条件性行为反应的影响。发现注射APV后对CA_3区突触效应的习得性长时程增强的产生有显著的抑制性影响,相应地条件性饮水反应的建立也受到显著的抑制,提示NMDA受体参与习得性LTP的产主。     

海马CA_3区习得性LTP的进一步探讨

分辨学习中大鼠ＰＰ－ＣＡ_３突触效应有习得性ＬＴＰ产生,进一步观察到ＭＦ－ＣＡ_３及Ｃｏｍｍ－ＣＡ_３也同步地产生习得性ＬＴＰ,表明几种输入突触都产生习得性ＬＴＰ,而ＭＦ－ＣＡ_３突触效应增强的程度则较Ｃｏｍｍ－ＣＡ_３的为大（Ｐ＜０．０１）。海马ＣＡ_３注入印防己毒素能易化ＰＰ－ＣＡ_３突触习得性ＬＴＰ的产生,工作发现一侧海马ＣＡ_３注印防己毒素,易化对侧ＭＦ－ＣＡ_３突触习得性ＬＴＰ的产生,表明两侧海马ＣＡ_３区在其习得性ＬＴＰ的形成上是相互协同的。     

LTP诱导期向维持或转化过程中的突触形态学特征

该研究探讨了视皮层LTP由诱导期向维持期转化过程的突触形态学特征。实验选用18-30天龄的健康SD大鼠,分实验组、空白对照组及实验对照组进行电镜观测和图象分析。结果发现,在常规LTP实验程序中强直刺激后有LTP产生并记录80分钟的实验组脑片标片,局部有界面曲率大于2的较大U型突触形成,这种突触多有两个以上活性区。图象分析结果显示,实验组与对照组相比较,突触的界面曲率明显增大（P＜0．05）,活性区的长度明显加长（＜0．05）。     

LTP诱导期向维持或转化过程中的突触形态学特征

该研究探讨了视皮层ＬＴＰ由诱导期向维持期转化过程的突触形态学特征。实验选用１８－３０天龄的健康ＳＤ大鼠,分实验组、空白对照组及实验对照组进行电镜观测和图象分析。结果发现,在常规ＬＴＰ实验程序中强直刺激后有ＬＴＰ产生并记录８０分钟的实验组脑片标片,局部有界面曲率大于２的较大Ｕ型突触形成,这种突触多有两个以上活性区。图象分析结果显示,实验组与对照组相比较,突触的界面曲率明显增大（Ｐ〈０．０５）,活性区     

海马齿状回突触效应的习得性长时程增强

本实验应用慢性埋植电极技术以电生理学给合行为学的方法,观察大白鼠海马齿状回在以视觉和味觉信号为条件信号的条件反应的建立、巩固和消退过程中突触效应的变化。结果表明在明暗辨别学习中出现突触效应长时程增强(LTD),其保持时间的长短与巩固性训练的多少呈正相关,LTP消退,习得行为也消退。对照实验证明它并非测试本身所引起,提示此习得性LTP与学习和记忆活动是密切相关的。但在建立条件性味觉厌恶中,却无LTP出现。这就从突触水平上进一步证明我们提出的海马在不同感觉信息的记忆活动中其作用是不同的及海马不仅在记忆的形成,而且在其保持和再现中也有重要作用的观点。     

习得性长时程突触增强在学习各阶段中的变化

应用慢性埋植技术以电生理学结合行为学的方法,观察大鼠海马CA_3区锥体细胞在明暗辨别反应的建立、巩固、消退和再建立的连续过程中,突触效应的变化规律。结果:在条件反应的建立过程中,产生突触效应长时程增强(LTP);在条件反应的巩固过程中,LTP继续保持;在条件反应的消退过程中,LTP消退;在条件反应的再建立过程中,再次产生LTP。而这种习得性LTP的发展和变化超前于习得性行为的产生和改变。这是在同一动物身上实现了以往多项工作的连贯性观察,表明在动物学习活动的连贯的迅速改变的各个阶段,海马CA_3区有相应的对条件性行为有制约作用的习得性LTP的发生和改变。它为论证习得性LTP可能是学习和记忆的神经基础之一,提供了新的有力证据。     

转基因小鼠在学习记忆研究中的应用

综述了国内外运用转基因小鼠研究学习记忆的主要成果;分析探讨了某些基因表达的蛋白质,如NMDA受体,nociceptin受体,非受体酪氨酸激酸,Ca^2 和钙调素依赖性激酶,蛋白激酶A,蛋白激酶C,与cAMP反应成分结合的蛋白质,神经细胞粘附分子,神经生长因子等在学习记忆过程中的作用机制;初步探讨了学习记忆与LTP的关系。     

Differential Effect of TEA on Long-Term Synaptic Modification in Hippocampal CA1 and Dentate Gyrus in vitro

The effectiveness of tetraethylammonium (TEA) and high-frequency stimulation (HFS) in inducing long-term synaptic modification is compared in CA1 and dentate gyrus (DG) in vitro. High-frequency stimulation induces long-term potentiation (LTP) at synapses of both perforant path-DG granule cell and Schaffer collateral-CA1 pyramidal cell pathways. By contrast, TEA (25 mM) induces long-term depression in DG while inducing LTP in CA1. The mechanisms underlying the differential effect of TEA in CA1 and DG were investigated. It was observed that T-type voltage-dependent calcium channel (VDCC) blocker, Ni²⁺ (50 μM), partially blocked TEA-induced LTP in CA1. A complete blockade of the TEA-induced LTP occurred when Ni²⁺ was applied together with the NMDA receptor antagonist, D-APV. The L-type VDCC blocker, nifidipine (20 μM), had no effect on CA1 TEA-induced LTP. In DG of the same slice, TEA actually induced long-term depression (LTD) instead of LTP, an effect that was blocked by D-APV. Neither T-type nor L-type VDCC blockade could prevent this LTD. When the calcium concentration in the perfusion medium was increased, TEA induced a weak LTP in DG that was blocked by Ni²⁺. During exposure to TEA, the magnitude of field EPSPs was increased in both CA1 and DG, but the increase was substantially greater in CA1. Tetraethylammonium application also was associated with a large, late EPSP component in CA1 that persisted even after severing the connections between CA3 and CA1. All of the TEA effects in CA1, however, were dramatically reduced by Ni²⁺. The results of this study indicate that TEA indirectly acts via both T-type VDCCs and NMDA receptors in CA1 and, as a consequence, induces LTP. By contrast, TEA indirectly acts via only NMDA receptors in DG and results in LTD. The results raise the possibility of a major synaptic difference in the density and/or distribution of T-type VDCCs and NMDA receptors in CA1 and DG of the rat hippocampus.     

Alzheimer amyloid beta-peptide inhibits the late phase of long-term potentiation through calcineurin-dependent mechanisms in the hippocampal dentate gyrus

The perforant path projecting from the entorhinal cortex to the hippocampal dentate gyrus is a particularly vulnerable target to the early deposition of amyloid beta (Abeta) peptides in Alzheimer's brain. The authors previously showed that brief applications of Abeta at subneurotoxic concentrations suppressed the early-phase long-term potentiation (E-LTP) in rat dentate gyrus. The current study further examines the effect of Abeta on the late-phase LTP (L-LTP) in this area. Using multiple high-frequency stimulus trains, a stable L-LTP lasting for at least 3 h was induced in the medial perforant path of rat hippocampal slices. Bath application of Abeta(1-42) (0.2-1.0 microM) during the induction trains attenuated both the initial and late stages of L-LTP. On the other hand, Abeta(1-42) perfusion within the first hour following the induction primarily impaired the late stage of L-LTP, which resembled the action of the protein synthesis inhibitor emetine. Blockade of calcineurin activity with FK506 or cyclosporin A completely prevented Abeta-induced L-LTP deficits. These results suggest that Abeta(1-42) impaired both the induction and maintenance phase of dentate L-LTP through calcineurin-dependent mechanisms. In the concentration range effective for inhibiting L-LTP, Abeta(1-42) also reduced the amplitude of NMDA receptor-mediated synaptic currents in dentate granule cells via a postsynaptic mechanism. In addition, concurrent applications of Abeta(1-42) with the protein synthesis inhibitor caused no additive reduction of L-LTP, indicating a common mechanism underlying the action of both. Thus, inhibition of NMDA receptor channels and disruption of protein synthesis were two possible mechanisms contributing to Abeta-induced L-LTP impairment.     

强迫性冷水游泳应激对大鼠行为和海马神经颗粒素的影响

为考察应激对海马神经颗粒素含量和磷酸化水平的影响,以及神经颗粒素是否涉及应激所致行为效应的脑机制,采用强迫性冷水游泳应激模型,选取40只Sprague-Dawley大鼠,随机分为应激组、装置对照组和正常对照组1和正常对照组2。以旷场试验法测定应激前后大鼠行为的变化,以Western blotting技术测定大鼠海马区域神经颗粒素的总含量和磷酸化水平,并分析两者之间的相互关系。结果表明：应激组动物活动增加,表现出焦虑行为;而海马区域神经颗粒素含量降低,与对照组相比差异具有显著性;且多项行为指标的变化与海马神经颗粒素含量的改变呈显著相关。这些结果提示神经颗粒素有可能在应激所致焦虑行为中起作用,可作为预测应激所致焦虑行为的较为敏感的指标之一。慢性应激过程中海马区域没有发现神经颗粒素的磷酸化反应。     

Endogenous opioid peptides contribute to associative LTP in the hippocampal CA3 region

The medial and lateral perforant path projections to the hippocampal CA3 region display distinct mechanisms of long-term potentiation (LTP) induction, N-methyl-d-aspartate (NMDA) and opioid receptor dependent, respectively. However, medial and lateral perforant path projections to the CA3 region display associative LTP with coactivation, suggesting that while they differ in receptors involved in LTP induction they may share common downstream mechanisms of LTP induction. Here we address this interaction of LTP induction mechanisms by evaluating the contribution of opioid receptors to the induction of associative LTP among the medial and lateral perforant path projections to the CA3 region in vivo. Local application of the opioid receptor antagonists naloxone or Cys2-Tyr3-Orn5-Pen7-amide (CTOP) normally block induction of lateral perforant path-CA3 LTP. However, these opioid receptor antagonists failed to block associative LTP in lateral perforant path-CA3 synapses when it was induced by strong coactivation of the medial perforant pathway which displays NMDAR-dependent LTP. Thus strong activation of non-opioidergic afferents can substitute for the opioid receptor activation required for lateral perforant path LTP induction. Conversely, medial perforant path-CA3 associative LTP was blocked by opioid receptor antagonists when induced by strong coactivation of the opioidergic lateral perforant path. These data indicate endogenous opioid peptides contribute to associative LTP at coactive synapses when induced by strong coactivation of an opioidergic afferent system. These data further suggest that associative LTP induction is regulated by the receptor mechanisms of the strongly stimulated pathway. Thus, while medial and lateral perforant path synapses differ in their mechanisms of LTP induction, associative LTP at these synapses share common downstream mechanisms of induction.     

鸟类神经系统的长时程增强

揭示学习与记忆的神经机制已成为认知科学领域的一个重要研究方向。研究过程中需根据不同实验目的选用不同实验动物。LTP（long-term potentiation）是一种研究学习记忆突触基础的主要模型,其代表突触功能的可塑性。以往对LTP的研究主要集中于哺乳动物,但由于鸟类在生物进化上具有独特的地位及特有的学习记忆能力,因此通过某些鸟类行为模型将有利于对LTP特性及其与学习记忆相关性进行更深入的探索。     

长期双酚A暴露对成年小鼠恐惧记忆的影响

双酚A (bisphenol, BPA)是一种广泛应用于塑料制品的环境内分泌干扰物, 具有弱雌激素和抗雄激素活性, 与雌激素受体有一定的亲和力。本实验探讨长期BPA暴露对成年小鼠恐惧记忆的影响及其神经机制。将9周龄雄性小鼠暴露于BPA (0.4、4、40 mg/kg/d) 90 d, 建立小鼠亚慢性BPA暴露模型后, 进行场景性条件恐惧训练, 然后分别在电击后1 hr及24 hr检测小鼠的僵立时间, 同时在电击前、电击后1 hr及24 hr检测海马相关蛋白表达变化。结果表明, BPA (4、40 mg/kg/d)暴露延长小鼠场景性条件恐惧训练后1 hr及24 hr的僵立时间。Western blot蛋白检测结果显示, 行为训练前, BPA降低了小鼠NMDA受体NR1亚基表达水平, 上调组蛋白去乙酰化酶2表达。行为训练后1 hr及24 hr, BPA促进海马NMDA受体亚基NR1和组蛋白H3乙酰化表达, 抑制组蛋白去乙酰化酶2表达, 同时促进ERK1/2磷酸化水平。以上结果表明, 长期BPA暴露提高成年小鼠恐惧记忆获得的同时延长恐惧记忆的保持; 该作用可能通过激活海马的ERK1/2通路而改变核内组蛋白乙酰化和NMDA受体水平进行。