CREB依赖的突触长时程增强

目的:探究LTP与CREB依赖的级联反应间的相关机制,阐述CREB依赖的生化系统网络的动力学行为特征。方法:依据突触可塑性相关的cAMP-PKA-CREB信号转导通道,假定蛋白激酶AC8是CREB的下游调节靶目标并反馈调节上游通道,构建了一个嵌有CREB依赖的正反馈环的cAMP-PKA-CREB分子模型。结果:CREB依赖的正反馈存在时,模型是一个鲁棒的双稳系统;阻断CREB依赖的正反馈后,模型变成一个单稳系统。结论:CREB依赖的正反馈可能是系统存在鲁棒的双稳特性的一个重要条件;嵌有CREB依赖的正反馈的cAMP-PKA-CREB分子系统可能是决定突触长时程增强诱导和维持的导向机制之一。     

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     

在脑片水平上突触可塑性长时程增强的研究进展

长时程增强(LTP)是突触效能的重要表现形式,是研究学习与记忆突触机制的客观指标.近年来随着脑片技术的发展,很多关于LTP的实验研究都在脑片水平上进行.介绍了海马脑片CA1区LTP的调节表达机制的研究,海马脑片上诱导产生的LTP的特征和脑片条件的关系,多巴胺转运蛋白阻断剂通过活化D3多巴胺受体增强海马脑片CA1区LTP,以及激活大鼠海马脑片CA1区突触β-肾上腺素能受体增强联合LTP的研究,综述了在脑片水平上研究LTP的诱导表达维持及调节等方面的研究动态和进展.     

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     

突触传递的长时程抑制的研究进展

突触传递的长时程抑制 (LTD)和长时程增强 (LTP)是行为依赖性突触可塑性的两种重要形式 ,一直以来都是研究学习记忆的热点。本文就近年来有关LTD的分子生物学机制和在学习记忆中的作用作一综述。     

尼氟酸抑制慢性内脏痛大鼠海马CA1区突触长时程增强

目的:探讨尼氟酸(HCN2特异性阻断剂)对慢性内脏痛大鼠海马CA1(cornu ammonis 1)区突触长时程增强(LTP)的影响。方法:选用新生SD大鼠(雌雄不分)出生后8～14 d内,每天固定时间给予1次60 mmHg压力的结直肠扩张刺激建立慢性内脏痛模型,大鼠成年后通过测量腹外斜肌对结直肠扩张引起的放电反应来评估肠道痛觉的敏感性。采用离体脑片场电位的记录方法,观察慢性内脏痛大鼠海马CA1区场电位LTP的变化,并观察不同浓度(25～75 mg/L)的尼氟酸对慢性内脏痛大鼠海马CA1区场电位LTP的影响。结果:慢性内脏痛大鼠海马基础场电位的幅值及斜率与正常大鼠比较无显著性差异,但高频刺激后模型大鼠诱导出的LTP幅值及斜率的变化率与正常大鼠比较均显著增加(P<0.05);尼氟酸对正常大鼠离体海马场电位LTP的峰值和斜率没有任何影响,但是不同剂量(25～75 mg/L)的尼氟酸可剂量依赖性显著降低慢性内脏痛大鼠离体海马场电位LTP的峰值及斜率。结论:HCN2通道可能参与慢性内脏痛大鼠海马场电位LTP的易化过程。     

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。     

酪氨酸蛋白激酶依赖性大鼠基底外侧杏仁核的长时程增强

目的 比较不同时间间隔的两串θ频率波刺激在大鼠离体脑片基底外侧杏仁核(BLA)长时程增强(LTP)形成中的作用,并探讨BLA的LTP是否为酪氨酸蛋白激酶(TPK)依赖性.方法 制备杏仁核脑片,刺激外囊记录BLA场电位,应用两串θ频率波刺激诱导LTP,每串θ频率波刺激为20个(频率5Hz)短时间高频串脉冲(5个脉冲,频率为100Hz),通过改变两串θ频率波的刺激间隔,分析不同参数诱导的LTP是否存在差异,并在灌流的人工脑脊液中加入TPK抑制剂genistein,观察其对杏仁核I胛的影响.结果 间隔10s的两串θ频率波未能在BLA诱导出LTP;增大串刺激间隔为10min或30min,均可观察到记录的场电位(f-EPSPs)明显增大,增强的场电位持续时间超过30min,串间隔为10min的参数诱导的LTP最明显;两串θ频率波刺激诱导的LTP可被TPK抑制剂genistein所阻断.结论 串间隔为10min的两串θ频率波刺激(TBS)是BLA诱导LTP的较好参数;杏仁核的LTP可能涉及TPK的激活.     

Brain-derived neurotrophic factor expression after long-term potentiation

Long-term potentiation (LTP) of perforant-path dentate granule cell synapses, in awake rats, was followed by a time-dependent expression of brain-derived neurotrophic factor (BDNF) mRNA in dentate granule cells. This BDNF expression was blocked by the (NMDA) antagonist dizocilpine maleate (MK-801), which also blocked LTP induction, and by sodium pentobarbital, which shortens LTP persistence. These results suggest that BDNF may participate in the NMDA-receptor mediated cascade of events that result in LTP stabilization.     

Calcium-induced long-term potentiation in the hippocampus

The effect of a transient increase in extracellular calcium concentration on the Schaffer collateral-commissural evoked excitatory postsynaptic potential and population spike responses of CAI pyramidal neurons was investigated using the rat in vitro hippocampal slice preparation. Brief exposure of slices (5-10 min) to twice the normal concentration of calcium (4 mM) induced a marked potentiation of both the excitatory postsynaptic potential and population spike that could persist for at least 3 h. No long-term changes were observed in either the presynaptic fiber volley of antidromically evoked CAI population spike, indicating that the potentiation could not be attributed to an increase in the number of fibers activated or a generalized increase in cellular excitability. The response of CAI pyramidal neurons to the iontophoretic application of L-glutamate in the apical dendritic zone was also unaffected after exposure to high calcium perfusate, suggesting a lack of alteration in membrane excitability or receptor sensitivity restricted to the region of synaptic input. In addition, total intracellular calcium content of individual slices, measured by atomic absorption spectrophotometry, was significantly increased for at least 1 h following return to the control medium. These data indicate that brief exposure of in vitro hippocampal slices to a high extracellular calcium concentration results in a long-term increase in synaptic efficacy which is similar in many respects to long-term potentiation induced by tetanic stimulation of hippocampal excitatory afferents. The results further suggest that the mechanisms underlying calcium-induced long-term potentiation may reside in presynaptic components and involve an enhanced transmitter release.     

Cyclic mechanical strain induces NO production in human patellar tendon fibroblasts – a possible role for remodelling and pathological transformation

The mechanism by which tendon fibroblasts can detect strain forces and respond to them is fairly unknown. Nitric oxide (NO) is a messenger molecule that among others can respond to shear stress in endothelial cells. Therefore, it was investigated whether cyclic mechanical strain induces NO in vitro in human patellar tendon fibroblasts. Human patellar tendon fibroblasts were cultured from remnants of patellar tendon transplants after reconstructive surgery. Fibroblasts were cultured on elastic silicone dishes. The cells were longitudinally strained (5%, 1 Hz) for 15' or 60'. As a control, no strain was applied. The experiments were finished after 0', 5', 15', and 30'. NO was determined using the Griess reaction. 15' strain showed at 0' and 5' 200% activation, which thereafter at 15' and 30' returned to normal levels. 60' strain showed a biphasic pattern. At 5' and 30', NO levels were increased to 175%. At 15', NO measurement displayed 120% increased levels. Mechanical strain induces NO production by tendon fibroblasts. Therefore, NO produced by tendon fibroblasts, as a response to alteration in their mechanical microenvironment, could modulate fibroblast function. The results of our study suggests that strain-related adaptive changes may, at least in part, be controlled by a process in which strain-related NO production from the fibroblast network may play a pivotal role. Moreover, these are basic findings that are important for further unravelling pathophysiology of tendon diseases.     

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.     

Long-term cholinergic enhancement of evoked potentials in rat hindlimb somatosensory cortex displays characteristics of long-term potentiation

Pairing a cutaneous electrical stimulus of the hind-paw with stimulation of the basal forebrain produces long-term cholinergic enhancement of the responsiveness to a tactile stimulus. A short period of pairing (20 trials) increased the area of the two main components of the evoked potential by 37.1 +/- 13.5% (+/- SEM) and 37.9 +/- 6.8%, respectively. The effects lasted for the duration of the experiment (> 2 h). The enhancement could be blocked by either MK-801, an NMDA receptor antagonist or by L-NAME, a nitric-oxide-synthase inhibitor when they were given prior to pairing. Control experiments with skin stimulation alone and basal forebrain stimulation alone had only small long-term effects (approximately 10%) on the size of the evoked potential. Thus, long-term cholinergic enhancement, attributable to disinhibition and increased release of acetylcholine in the cortex during neuronal excitation by other sources, and so named because it is blocked by atropine, may be a form of long-term potentiation. The existence of such a mechanism for the control of cortical neuronal plasticity identifies the basal forebrain as a powerful modulator of long-lasting changes in cortical neuronal excitability.     

Impairment of recognition memory and hippocampal long-term potentiation after acute exposure to clioquinol

Clioquinol (CQ) was associated with cases of transient global amnesia and with the neurodegenerative syndrome subacute myelo-optico-neuropathy (SMON) in humans. However, CQ forms lipophilic chelates with cations and has the potential as a scientific and clinical tool used for selective modulation of histochemically reactive zinc pools. The relationship among transient lack of synaptic zinc release, hippocampal long-term potentiation (LTP) induction and cognitive memory is poorly understood. To evaluate the role of synaptic zinc release, in the present study, hippocampal LTP induction and cognitive behavior were examined in young rats after i.p. injection of CQ (30 mg/kg). Intracellular zinc detected by Timm's stain and extracellular (synaptic cleft) zinc detected by ZnAF-2 were significantly decreased in the hippocampus 6 h after CQ injection. The molecular layer of the dentate gyrus, in which perforant path-granule cell synapses exist, was most responsive to CQ injection. Dentate gyrus LTP was induced similarly to the control 2 h after CQ injection, while significantly attenuated 6–24 h after CQ injection. In the training trial of the object recognition memory 2 h after CQ injection, there was no significant difference in learning behavior between the control and CQ-treated rats. In the test trial, CQ-treated rats showed normal recognition memory 1 h after the training, whereas recognition memory deficit 24 h after the training unlike the control rats. These results indicate that acute exposure to CQ impairs long-term (24 h) memory in the hippocampus of young rats. The CQ-mediated attenuation of dentate gyrus LTP, which may be associated with the transient lack of zinc release from zincergic neurons, seems to be involved in the impairment of the long-term memory.     

Alpha v integrins mediate beta-amyloid induced inhibition of long-term potentiation

Beta-amyloid (Aβ) is the principal component of the extracellular plaques present in patients with Alzheimer's disease. Several studies have recently shown that acutely applied Aβ inhibits the induction of LTP in the hippocampus. In the present studies, we have investigated the role of integrins in such Aβ-mediated block of LTP in the dentate gyrus in vitro and in the CA1 in vivo. Selective antibodies to the αv integrin subunit were found to prevent the Aβ inhibition of LTP, both in the dentate gyrus in vitro and in the CA1 in vivo. In contrast, two control antibodies did not prevent such action of Aβ. In addition, a small molecule nonpeptide antagonist of αv-containing integrins and two other antagonistic ligands of integrins, superfibronectin and the disintegrin echistatin, also prevented the Aβ inhibition of LTP. These studies indicate that αv integrins may be important mediators of synaptic dysfunction prior to neurodegeneration in Alzheimer's disease.     

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.     

流体剪切力对大鼠成骨样细胞生成NO的调节作用

机械应力在骨改建中起着重要的作用。本研究试图探讨机械应力刺激调节成骨细胞生理功能过程中一氧化氮 (NO)的作用机制。通过流室系统对体外培养的大鼠成骨样细胞施加 12 dyn/ cm2的流体剪切力 ,采用 NO荧光检测试剂盒检测细胞受力 5、10、15、30、6 0、12 0 min后不同时段的 NO的表达。结果表明 ,大鼠成骨样细胞受力后生成的 NO明显高于空白对照组 (P<0 .0 5 )。受力细胞在受力后 6 0 min内 ,NO的生成在各时段无明显提高 ,但在6 0 m in后开始明显增加 (P<0 .0 5 )。而空白对照组各时段 NO的生成无显著性差异 (P>0 .0 5 )。机械应力作用下 ,成骨样细胞早期释放 NO,可能是骨组织细胞将机械应力刺激转导入细胞 ,促进骨形成的生化信号分子。流体剪切力刺激诱导的反应早期可能是直接通过激活 c NOS的生化通道来实现 ,在后期可能是通过 i NOS的途径     

Enriched environment restores impaired hippocampal long-term potentiation and water maze performance induced by developmental lead exposure in rats

Lead (Pb2+) exposure in children can induce long lasting deficits in cognitive function and has been modeled in experimental animals. Based on previous studies which demonstrated that learning impairments resulting from developmental Pb2+ exposure were reversible if the animals were provided with an enriched environment, here, we asked if environmental enrichment (EE) could also reverse long-term potential (LTP) impairment induced by lead. Rats drank 1,500 ppm lead acetate (PbAc) solution or distilled water throughout gestation and lactation. After weaning at postnatal Day 22, one half of the control and lead-exposed male offspring were given the environmental enrichment treatment through all the experiments until tested. Electrophysiological and Morris water maze test were performed at 8 weeks of age. The result showed that the impaired learning ability induced by lead could be reversed by EE. Furthermore, our results revealed that EPSP LTP and PS LTP impairments induced by lead were also reversible by EE experience.