海马CA_3区辐射层突触形态的衰老性变化

本文应用电镜体视学和半自动图像分析系统对青年组(3个月),老年组(34个月),SD大白鼠海马CA_3区辐射层的突触进行研究,结果显示老年组突触数密度、面密度、突触平均长度,可见线粒体突触前终未数均比青年组减少,突触切面长度未见明显的代偿性变化,表明海马CA_3区辐射层突触在老年时出现退行性变化。本文并对突触丢失,退变及其意义进行讨论。     

促红细胞生成素对β淀粉样蛋白诱导大鼠海马损伤的保护作用以及对大鼠学习记忆的影响

目的:探讨促红细胞生成素(erythropoietin,EPO)对阿尔茨海默病(Alzheimer disease,AD)大鼠脑损伤的保护机制。方法:采用大鼠海马内注射β淀粉样蛋白制作AD模型。将SD大鼠随机分为正常对照组、生理盐水对照组及EPO处理组。Aβ1-40大鼠海马内注射造模,在生理盐水对照组大鼠行脑室立体定向注射生理盐水,EPO处理组则行脑室立体定向注射重组人促红细胞生成素(rHu-EPO)。观察手术后7 d海马CA1区细胞凋亡变化,及缺血造模后4周大鼠学习和记忆力的变化。结果:EPO处理组大鼠海马CA1区凋亡细胞较生理盐水对照组减少(P<0.01),EPO处理组大鼠学习记忆能力明显高于生理盐水对照组(P<0.05)。结论:EPO可以抑制Aβ1-40诱导海马CA1区细胞凋亡,保护AD大鼠学习记忆功能。     

D-半乳糖导致小鼠海马基因表达谱变化

本实验采用cDNA芯片研究D-半乳糖皮下注射小鼠海马的基因表达变化。小鼠皮下注射D-半乳糖[50m∥(kg．d)]60d造模，Morris水迷宫测试小鼠行为，分别提取模型组和对照组海马组织总RNA，掺入荧光分子Cy3和Cy5，经逆转录合成cDNA荧光探针与4000点小鼠cDNA基因芯片杂交。结果显示，在4000条待研究的基因中，两组小鼠海马间存在2倍表达差异的有76条，其中上调26条，下调50条。经分析，模型组基因表达谱与老年性痴呆(AD)相关基因表达谱在氧应激、能量代谢相关基因等方面有相似之处。提示D-半乳糖小鼠模型有可能作为拟AD病理模型。     

Timing and efficacy of transmitter release at mossy fiber synapses in the hippocampal network

It is widely accepted that the hippocampus plays a major role in learning and memory. The mossy fiber synapse between granule cells in the dentate gyrus and pyramidal neurons in the CA3 region is a key component of the hippocampal trisynaptic circuit. Recent work, partially based on direct presynaptic patch-clamp recordings from hippocampal mossy fiber boutons, sheds light on the mechanisms of synaptic transmission and plasticity at mossy fiber synapses. A high Na⁺ channel density in mossy fiber boutons leads to a large amplitude of the presynaptic action potential. Together with the fast gating of presynaptic Ca²⁺ channels, this generates a large and brief presynaptic Ca²⁺ influx, which can trigger transmitter release with high efficiency and temporal precision. The large number of release sites, the large size of the releasable pool of vesicles, and the huge extent of presynaptic plasticity confer unique strength to this synapse, suggesting a large impact onto the CA3 pyramidal cell network under specific behavioral conditions. The characteristic properties of the hippocampal mossy fiber synapse may be important for pattern separation and information storage in the dentate gyrus-CA3 cell network.     

Evidence of reorganization in the hippocampal mossy fiber synapses of adult rats rehabilitated after prolonged undernutrition

We have previously demonstrated that prolonged low-protein diet leads to irreversible cell loss in the hippocampal formation of the adult rat. Because the extent of the resulting hippocampal synaptic alterations is not well characterized, we studied the contacts between mossy fibers and the dendritic excrescences of CA3 pyramidal cells (MF-CA3 synapses) using quantitative methods. Moreover, we investigated whether rehabilitation from undernutrition would influence the morphology of hippocampal synapses. To address these issues, three groups of adult rats were compared: (a) rats fed with a normal diet for 12 months (control rats); (b) rats treated during the same period with low-protein diet (undernourished rats); and (c) rats undernourished for 6 months and then switched to normal diet for 6 months (recovery rats). Timm staining and electron microscopy were employed to estimate the volume of the mossy fiber system and the number and related quantitative features of MF-CA3 synapses. The volume of the suprapyramidal bundle of the mossy fiber system and its total number of synapses were smaller in undernourished rats than in control and recovery animals. These parameters did not differ between the latter two groups. The size of mossy fiber terminals and dendritic excrescences and the surface area of synapses were smaller in undernourished than in control and recovery groups. Conversely, in recovery animals, the volume of the suprapyramidal bundle of the mossy fiber system, the size of mossy fiber terminals and dendritic excrescences, and the total number and surface area of synapses were similar to those of controls. These findings indicate that, following rehabilitation, the pre- and postsynaptic compartments of MF-CA3 synapses undergo structural alterations which compensate for the neuronal loss induced by undernutrition.     

二苯乙烯苷对沙鼠脑缺血/再灌注引发海马损伤的保护作用

目的　研究二苯乙烯苷（tetrahydroxy stilbene glucoside, TSG）对脑缺血/再灌注（ischemia/reperfusion, I/R）沙鼠脑海马损伤的保护作用及可能机制。 方法 采用结扎沙鼠双侧颈动脉缺血30 min,再灌注5 d复制沙鼠全脑I/R模型。沙鼠随机分为6组,假手术组、模型对照组、TSG大、中、小剂量（6、3、1.5 mg/kg）组和阳性对照药依达拉奉注射组（3 mg/kg）。5 d后通过Morris水迷宫测定沙鼠学习记忆功能;Nissl染色观察沙鼠大脑海马CA1区神经元结构和数量的变化;TUNEL染色法观察沙鼠大脑海马CA1区神经元凋亡的变化;Western blot法检测脑组织active-caspase-3的表达。 结果　与假手术组相比,I/R组沙鼠学习记忆能力明显降低,海马CA1区神经元大量丢失,结构紊乱。同时,I/R组沙鼠CA1区神经元凋亡数量明显增加,脑组织中caspase-3显著活化。TSG中、高（3、6 mg/kg）剂量组和依达拉奉阳性对照组均可以显著改善I/R引发的沙鼠学习记忆能力的降低,抑制海马CA1区神经元的丢失,改善神经元结构;抑制CA1区神经元的凋亡以及caspase-3的活化。而TSG低剂量组对上述变化均没有明显的治疗作用。 结论　TSG对于I/R引发的脑损伤,尤其是海马区神经元迟发性凋亡具有明显的治疗作用,这种作用与其抑制caspase-3的活化相关。     

大鼠脊髓腰节段神经营养因子及其受体的增龄变化

目的 观察不同月龄(1、3、6、12、18和24月龄)大鼠脊髓腰节段神经营养因子及其受体的变化,探讨其与增龄之间的关系。方法 用免疫组织化学和Western blot 法观察脊髓腰节段神经营养因子及其受体的表达,用尼氏染色法观察脊髓腰节段存活神经元数量。结果 大鼠脊髓腰节段神经生长因子(NGF)及其受体TrkA、脑源性神经营养因子(BDNF)及其受体TrkB和胶质细胞源性神经营养因子(GDNF)表达具有明显的随增龄变化规律,即1月龄（幼年期）时表达量较低,随年龄增高逐渐上升,至6月龄（青年期）达高峰,24月龄（老年期）明显减低,其中以GDNF的变化更为明显。大鼠脊髓腰节段存活神经元数量在1月龄至6月龄均保持在较高水平,之后开始逐渐下降,24月龄时降至最低。结论 神经营养因子及其受体在大鼠脊髓腰节段中的表达存在增龄变化,特别是老年期表达量显著降低,可能是导致脊髓老化的重要机制之一。     

Alzheimer病模型大鼠海马生长抑素神经元变化

目的：检测早老型痴呆(Alzheimer,AD)模型大鼠海马内生长抑素(Somatostatin,SS)神经元变化。方法：模型组用D-半乳糖和鹅膏蕈氨酸(Ibotenic acid,IBO)损毁Meynert核联合造模。运用免疫组化ABC法结合图像分析,检测并统计2组大鼠海马SS阳性神经元数目、截面积和灰度值。结果：模型组大鼠海马生长抑素神经元数目减少明显,灰度值增加明显,组间差异显著;生长抑素神经元胞体截面积无明显变化。结论：D半乳糖合并IBO损毁双侧Meynert核所致AD大鼠海马生长抑素神经元衰退明显。     

一氧化氮对大鼠学习记忆和胆碱能系统的影响

目的:探讨一氧化氮(nitric oxide,NO)在大鼠空间学习和记忆过程中的作用及其对胆碱能受体作用机制。方法:大鼠侧脑室分别注射NO前体左旋精氨酸(L-arginine,L-Arg,L-Arg组)、α7烟碱型乙酰胆碱受体(α7nicotinic acetylcholine receptor,α7nAChR)拮抗剂甲基牛扁亭(methyllycaconitine,MLA,MLA组)、α7nAChR激动剂氯化胆碱(choline chloride,CC组)、一氧化氮合酶抑制剂Nω-硝基-L-精氨酸甲酯(nω-nitro-L-arginine methylester,L-NAME,L-NAME组)以及先注射MLA再注射L-Arg(ML组)、先注射L-NAME再注射氯化胆碱(NC组),并以等量生理盐水(NS组)作为对照。用Y型迷宫刺激器、硝酸还原酶法、免疫组织化学以及Western-Blot等技术分别检测大鼠空间学习和记忆行为能力、大脑皮质和海马NO含量和α7nAChR的表达。结果:与对照组比较,Y迷宫空间学习能力达标次数和24 h后30次测试记忆行为中错误反应次数在L-Arg组和CC组均减少,而在MLA组和L-NAME组均增多;大脑前额叶皮质和海马NO含量和α7nAChR阳性细胞数以及蛋白含量在L-Arg组和CC组均明显增多,而在MLA组和L-NAME组均明显减少。ML组和NC组分别与L-Arg和CC组相比较,大鼠学习和记忆行为能力均明显减弱,并且大脑前额叶皮质和海马NO含量以及α7nAChR的表达均减少。结论:侧脑室应用MLA或L-NAME可减弱L-Arg或氯化胆碱对大鼠空间学习和记忆行为能力的促进作用;NO通过α7nAChR促进大鼠空间学习和记忆能力。     

老年雌性和雄性大鼠学习记忆能力比较

目的观察老年雌、雄性wistar大鼠的学习记忆能力的差异,进一步探索雌激素对学习记忆的影响。方法26只18月龄健康Wistar大鼠,其中雌性16只,雄性10只,在相同环境中饲养2个月后,用Morris水迷宫测试并分析其学习记忆能力的差异。结果在各时段老年雌性大鼠的逃避潜伏期均长于老年雄性大鼠,第5～9时段雌性大鼠的逃避潜伏期显著高于雄性大鼠(P<0.01),雌性大鼠的穿台次数显著低于雄性大鼠(P<0.05)。结论雌激素撤退在老年雌性大鼠学习记忆能力下降的中起到了主要作用。     

灵芝多糖对阿尔茨海默病大鼠学习记忆影响及与海马细胞凋亡的关系

目的:观察灵芝多糖(GLP)对阿尔茨海默病(AD)模型大鼠学习记忆影响并探讨其与海马细胞凋亡的关系。方法:用立体定位技术对海马CA1区微量注射Aβ25~35造成AD模型;Morris水迷宫检测大鼠记忆水平;电子显微镜、流式细胞仪检测海马凋亡。结果:GLP可明显提高Aβ25~35所致痴呆大鼠学习记忆水平,显著降低海马细胞凋亡率。结论:GLP对AD大鼠的保护作用与降低海马细胞凋亡率有关。     

Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.     

老龄大鼠海马结构脑源性神经营养因子表达的改变

目的：探讨大鼠海马结构脑源性神经营养因子（BDNF）表达的老龄性改变，为脑衰老提供可靠的免疫组织化学资料。方法：选用雌性Wistar大鼠24只，分为青年组和老龄组。应用免疫组化方法结合图像分析技术对2组大鼠海马结构BDNF阳性产物进行定性、定量分析。结果：老龄组海马CA3和CA1区神经元BDNF含量比青年组分别下降了13．3％、10．4％，然而，齿状回从青年到老年变化不显著。结论：老龄时海马CA3和CA1区神经元的BDNF表达发生了明显的变化，其含量明显降低。提示老龄大鼠海马CA3和CA1区神经元BDNF表达的改变，可能是老龄动物海马结构营养及学习记忆障碍的形态学基础。     

Effects of age on axon terminals forming axosomatic and axodendritic inhibitory synapses in prefrontal cortex

Much of the cognitive decline shown by aging primates can be attributed to dysfunction of prefrontal cortex and, as shown previously, about 30% of asymmetric (excitatory) and symmetric (inhibitory) axodendritic synapses are lost from the neuropil of layer 2/3 in prefrontal area 46 with age [Peters A, Sethares C, Luebke JI (2008) Neuroscience 152:970–981]. Whether there is a similar loss of inhibitory axosomatic synapses from this cortex has not been determined, but a study in primate motor cortex suggests that axosomatic synapses are not lost with age [Tigges J, Herndon JG, Peters A (1992) Anat Rec 232:305–315]. The present study is focused upon whether the remaining axon terminals forming inhibitory synapses in old monkeys hypertrophy to compensate for any age-related loss. Analysis of electron micrographs show that in layer 2/3 of area 46 in both young and old monkeys, axon terminals forming axosomatic synapses are significantly larger and contain more mitochondria than those forming axodendritic synapses and both axodendritic and axosomatic terminals become larger with age. However, while mitochondria in axodendritic terminals do not change in either size or amount with age, the mitochondria in axosomatic terminals become larger. Similarly, in terminals forming axodendritic synapses, the mean numbers of synaptic vesicle profiles is the same in young and old monkeys, whereas in terminals forming axosomatic synapses there is an increase in the numbers of synaptic vesicles with age. We also show that among these age-related changes, only the numbers of synaptic vesicles in axosomatic synapses are significantly correlated with the cognitive impairment indices displayed by the same monkeys. In summary, the data provide original evidence that axosomatic axon terminals increase in size and in their content of mitochondria and synaptic vesicles. Furthermore, based on our and previously published results, we speculate that these changes are linked to age-related cognitive decline.     

Cholinergic drug effects and brain muscarinic receptor binding in aged rats

Muscarinic systems are significantly altered in the brains of laboratory animals and man as a result of normal aging. Cholinergic neurotransmission in cerebral cortex and hippocampus is also severely impaired in a major age-related neurological disorder. Alzheimer's disease. The objective of these studies was to assess specific ³H-quinuclidinyl benzilate (³H-QNB) binding to brain muscarinic receptors in young, adult and senescent Fischer 344 rats, and to relate receptor changes to differences in the pharmacologic actions of cholinergic drugs. Muscarinic receptor density declined with advanced age in the frontal cortex, corpus striatum and hypothalamus, but no age-related changes in receptor affinity were observed. Specific binding of ³H-QNB in hippocampus was not significantly altered. In contrast, the in vivo effects of oxotremorine (hypothermia and antinociception) were markedly enhanced in aged rats, whereas scopolamine-induced locomotor activity was reduced. Hence, senescent rats were more sensitive to the pharmacologic actions of a cholinergic agonist, but less responsive than young rats to a muscarinic antagonist. These seemingly contradictory results of binding experiments and pharmacological studies could be due, in part, to changes in subtypes of brain muscarinic receptors with advanced age. Alternatively, the age-related differences in cholinergic drug effects may reflect a decreased ability of the senescent animal to adapt to changes in its environment.     

单侧磨牙缺失对老年学习记忆减退大鼠基底前脑胆碱能系统的影响

目的:探讨单侧缺牙对不同学习记忆能力老年大鼠基底前脑胆碱能系统的影响。方法:用Morris水迷宫筛选出老年记忆减退鼠和老年记忆正常鼠,拔除单侧磨牙后2个月,用免疫组化和组织化学染色观察对其斜角带核垂直支胆碱能神经元和海马CA1区、前额皮质胆碱能纤维密度的影响。结果:斜角带核垂直支ChAT阳性细胞数和海马CA1区、前额皮质AChE阳性纤维密度在老年记忆减退鼠中,拔牙组较对照组(未拔牙)明显下降;海马CA1区AChE阳性纤维密度在老年记忆正常鼠中,拔牙组较对照组明显下降。结论:单侧磨牙缺失可加速老年学习记忆减退鼠基底前脑胆碱能系统的损害。     

Ultrastructure of synapses in cerebral cortex layer i in rats with low and high resistance to hypoxia

Quantitative analysis of synapses in layer I of the sensorimotor cortex in rats with low resistance to hypoxia revealed pronounced changes in the number of synaptic vesicles docked at the presynaptic membrane in active synaptic zones under conditions of acute hypobaric hypoxia. In high-resistant animals the number of docked synaptic vesicles under these conditions remained unchanged. In was hypothesized that high sensitivity to hypoxia in low-resistant rats is determined by high reactivity of the synaptic transmission system.     

Amyloid β peptide levels and its effects on hippocampal acetylcholine release in aged, cognitively-impaired and -unimpaired rats

Excessive extracellular deposition of amyloid β (Aβ) peptide in neuritic plaques and degeneration of forebrain cholinergic neurones, which innervate the hippocampus and the neocortex, are the invariant characteristic features of Alzheimer's disease (AD). Studies of the pathological changes that characterize AD, together with several other lines of evidence, indicate that Aβ accumulation in vivo may initiate and/or contribute to the process of neurodegeneration observed in the AD brain. However, the underlying mechanisms by which Aβ peptide influences/causes degeneration of the basal forebrain cholinergic neurones in AD brains remain obscure. We reported earlier that nM concentrations of Aβ-related peptides, under acute conditions, can potently inhibit K⁺-evoked endogenous acetylcholine (ACh) release from the hippocampus and the cortex but not from striatum in young adult rats (J. Neurosci. 16 (1996) 1034). In the present study, to determine whether the effects of Aβ peptides alter with normal aging and/or cognitive state, we have measured Aβ_1–40 levels and the effects of exogenous Aβ_1–40 on hippocampal ACh release in young adult as well as aged cognitively-unimpaired (AU) and -impaired (AI) rats. Endogenous levels of Aβ_1–40 in the hippocampus are significantly increased in aged rats. Additionally, 10 nM Aβ_1–40 potently inhibited endogenous ACh release from the hippocampus of the three groups of rats, but the time-course of the effects clearly indicate that the cholinergic neurones of AI rats are more sensitive to Aβ peptides than either AU or young adult rats. These results, together with earlier reports, suggest that the processing of the precursor protein of Aβ peptide alters with normal aging and the response of the cholinergic neurones to the peptide possibly varies with the cognitive status of the animals.     

Caspase-6 activity predicts lower episodic memory ability in aged individuals

Caspase-6 (Casp6), a cysteinyl protease that induces axonal degeneration, is activated early in Alzheimer Disease (AD) brains. To determine whether Casp6 activation is responsible for early cognitive impairment, we investigated the abundance of Casp6 activity, paired helical filament–1 (PHF-1) phosphorylated Tau and amyloid beta peptide (Aβ) pathology by immunohistochemistry in the hippocampal formation of aged non–cognitively impaired (NCI) individuals. Casp6 activity was restricted to the entorhinal cortex (ERC) and CA1 regions of the hippocampus. Pathology scores were then correlated with cognitive scores obtained within 1 year of death. Regression analyses revealed that ERC and CA1 Casp6 activity were the main contributor to lower episodic memory performance, whereas ERC PHF-1 pathology predicted lower semantic and working memory performance. Aβ did not correlate with any of the cognitive tests. Because Casp6 activity and PHF-1 pathology are intimately associated with AD pathology and memory decline is an early event in AD, we conclude that Casp6 activity and PHF-1 immunoreactivity in ERC identifies aged individuals at risk for developing AD.