钙结合蛋白在老年人海马CA1和CA3区的分布

目的　探讨老年人海马中钙结合蛋白 (CalbindinD 2 8K ,CaBP)的分布及表达 ,并分析其在人衰老过程中对神经元的生理、病理变化的影响。方法　收集 12例 6 0岁以上老年人非脑部疾病尸检左侧大脑半球的海马组织 ,经病理常规处理后 ,切片 ,用免疫组织化学ABC染色法检测海马CA1与CA3区CaBP的分布。结果　CaBP阳性产物出现在神经元的细胞质中 ,CA1区的CaBP免疫阳性细胞数多于CA3区。结论　CaBP在老年人海马CA1、CA3中均有表达 ,但有差别。提示CaBP在老年人海马的功能活动中可能起重要作用。     

Age-related deterioration of long-term potentiation in the CA3 and CA1 regions of hippocampal slices from the senescence-accelerated mouse

Long-term potentiation (LTP) is one candidate for the mechanism underlying memory storage. In the present study, we carried out electrophysiological studies on hippocampal slices prepared from the senescence-accelerated mouse (SAM-P/8), a strain which shows accelerated senescence and failure of certain types of learning in behavioral tests. The findings were compared with those noted in the SAM-R/1 substrain without severe symptoms of senescence. No significant differences were found between SAM-R/1 and SAM-P/8 of the same ages in responses in the absence of tetanic stimulation, and in LTP after tetanic stimulation. However, there were marked decreases in the degree of potentiation with aging in both strains.     

Gamma oscillations dynamically couple hippocampal CA3 and CA1 regions during memory task performance

The hippocampal formation is believed to be critical for the encoding, consolidation, and retrieval of episodic memories. Yet, how these processes are supported by the anatomically diverse hippocampal networks is still unknown. To examine this issue, we tested rats in a hippocampus-dependent delayed spatial alternation task on a modified T maze while simultaneously recording local field potentials from dendritic and somatic layers of the dentate gyrus, CA3, and CA1 regions by using high-density, 96-site silicon probes. Both the power and coherence of gamma oscillations exhibited layer-specific changes during task performance. Peak increases in the gamma power and coherence were found in the CA3-CA1 interface on the maze segment approaching the T junction, independent of motor aspects of task performance. These results show that hippocampal networks can be dynamically coupled by gamma oscillations according to specific behavioral demands. Based on these findings, we propose that gamma oscillations may serve as a physiological mechanism by which CA3 output can coordinate CA1 activity to support retrieval of hippocampus-dependent memories.     

Long-term potentiation at single fiber inputs to hippocampal CA1 pyramidal cells.

Despite extensive investigation, it remains unclear whether presynaptic and/or postsynaptic modifications are primarily responsible for the expression of long-term potentiation (LTP) in the CA1 region of the hippocampus. Here we address this issue by using techniques that maximize the likelihood of stimulating a single axon and thereby presumably a single synapse before and after the induction of LTP. Several basic properties of synaptic transmission were examined including the probability of neurotransmitter release (Pr), the quantal size (q), and the so-called potency, which is defined as the average size of the synaptic response when release of transmitter does occur. LTP was routinely associated with an increase in potency, whereas increases in Pr alone were not observed. LTP was also reliably induced when baseline Pr was high, indicating that synapses with high Pr can express LTP. These results suggest that the mechanism for the expression of LTP involves an increase in q and is difficult to explain by an increase in Pr alone.     

大麻素受体在海马CA1区锥体神经元的功能表达

目的观察大麻素受体在孤立的海马CA1区锥体神经元的功能表达。方法将出生15~20d的Wistar大鼠取脑,急性分离出单个CA1区锥体神经元,用膜片钳技术记录神经元电活动,观察非选择性大麻素受体激动剂Win55212-2(5μmol/L)对神经元静息电位、动作电位、自发发放频率的影响。根据Win55212-2对膜电位的影响分为超极化组(n=7)和去极化组(n=6)。组织切片活性用MTT染色法检测。结果与给药前比较,超极化组神经元给药中动作电位频率和膜电压显著降低[0Hz vs(4.3±3.2)Hz,P0.05;(-57.0±4.6)mVvs(-54.1±3.8)mV,P0.01];与给药中比较,给药后动作电位频率及膜电压显著升高,差异有统计学意义(P0.01)。与给药前比较,去极化组神经元给药中动作电位频率显著降低,膜电压显著升高(P0.01);与给药中比较,给药后动作电位频率显著升高,膜电压显著降低,差异有统计学意义(P0.05)。结论 CA1区锥体神经元可能存在大麻素受体功能表达且不限于大麻素受体1;激活大麻素受体可能通过不同的机制起到抑制CA1区锥体神经元的作用。     

Active summation of excitatory postsynaptic potentials in hippocampal CA3 pyramidal neurons

The manner in which the thousands of synaptic inputs received by a pyramidal neuron are summed is critical both to our understanding of the computations that may be performed by single neurons and of the codes used by neurons to transmit information. Recent work on pyramidal cell dendrites has shown that subthreshold synaptic inputs are modulated by voltage-dependent channels, raising the possibility that summation of synaptic responses is influenced by the active properties of dendrites. Here, we use somatic and dendritic whole-cell recordings to show that pyramidal cells in hippocampal area CA3 sum distal and proximal excitatory postsynaptic potentials sublinearly and actively, that the degree of nonlinearity depends on the magnitude and timing of the excitatory postsynaptic potentials, and that blockade of transient potassium channels linearizes summation. Nonlinear summation of synaptic inputs could have important implications for the computations performed by single neurons and also for the role of the mossy fiber and perforant path inputs to hippocampal area CA3.     

Local generation of multineuronal spike sequences in the hippocampal CA1 region

Sequential activity of multineuronal spiking can be observed during theta and high-frequency ripple oscillations in the hippocampal CA1 region and is linked to experience, but the mechanisms underlying such sequences are unknown. We compared multineuronal spiking during theta oscillations, spontaneous ripples, and focal optically induced high-frequency oscillations (“synthetic” ripples) in freely moving mice. Firing rates and rate modulations of individual neurons, and multineuronal sequences of pyramidal cell and interneuron spiking, were correlated during theta oscillations, spontaneous ripples, and synthetic ripples. Interneuron spiking was crucial for sequence consistency. These results suggest that participation of single neurons and their sequential order in population events are not strictly determined by extrinsic inputs but also influenced by local-circuit properties, including synapses between local neurons and single-neuron biophysics.A hypothesized hallmark of cognition is self-organized sequential activation of neuronal assemblies (1). Self-organized neuronal sequences have been observed in several cortical structures (2–5) and neuronal models (6–7). In the hippocampus, sequential activity of place cells (8) may be induced by external landmarks perceived by the animal during spatial navigation (9) and conveyed to CA1 by the upstream CA3 region or layer 3 of the entorhinal cortex (10). Internally generated sequences have been also described in CA1 during theta oscillations in memory tasks (4, 11), raising the possibility that a given neuronal substrate is responsible for generating sequences at multiple time scales. The extensive recurrent excitatory collateral system of the CA3 region has been postulated to be critical in this process (4, 7, 12, 13).The sequential activity of place cells is “replayed” during sharp waves (SPW) in a temporally compressed form compared with rate modulation of place cells (14–20) and may arise from the CA3 recurrent excitatory networks during immobility and slow wave sleep. The SPW-related convergent depolarization of CA1 neurons gives rise to a local, fast oscillatory event in the CA1 region (“ripple,” 140–180 Hz; refs. 8 and 21). Selective elimination of ripples during or after learning impairs memory performance (22–24), suggesting that SPW ripple-related replay assists memory consolidation (12, 13). Although the local origin of the ripple oscillations is well demonstrated (25, 26), it has been tacitly assumed that the ripple-associated, sequentially ordered firing of CA1 neurons is synaptically driven by the upstream CA3 cell assemblies (12, 15), largely because excitatory recurrent collaterals in the CA1 region are sparse (27). However, sequential activity may also emerge by local mechanisms, patterned by the different biophysical properties of CA1 pyramidal cells and their interactions with local interneurons, which discharge at different times during a ripple (28–30). A putative function of the rich variety of interneurons is temporal organization of principal cell spiking (29–32). We tested the “local-circuit” hypothesis by comparing the probability of participation and sequential firing of CA1 neurons during theta oscillations, natural spontaneous ripple events, and “synthetic” ripples induced by local optogenetic activation of pyramidal neurons.     

老年小鼠海马CA1区轴棘突触微细结构的定量分析

目的观察老年小鼠海马CA1区轴棘突触相关结构的改变,为衰老引起的学习记忆减退提供神经解剖学依据。方法利用Golgi染色、超薄连续切片及NIH图像分析系统测量海马CA1区锥体细胞树突棘的密度、树突棘头及突触后致密斑的大小。结果海马CA1第2、3级顶树突的树突棘密度在3月龄组与22月龄组分别为(1.056±0.049)/μm和(0.868±0.038)/μm;穿孔型突触的比率3月龄与22月龄组分别为12.7%和19%。结论老年小鼠海马CA1区锥体细胞树突棘的减少、穿孔型突触比率的增加可能是衰老引起学习记忆减退的形态学基础。     

间歇缺氧大鼠海马神经元凋亡及其机制

目的探讨间歇缺氧对大鼠海马组织氧化应激状态及海马神经元凋亡的影响及其可能的机制。方法将36只雄性Wistar大鼠随机分为间歇缺氧组、持续缺氧组和正常对照组，每组12只。采用化学比色法测定海马组织丙二醛和超氧化物歧化酶（SOD）水平，应用Western免疫印迹法检测海马CA1区磷酸化C—JUN氨基末端激酶（p-JNK）、磷酸化c-jun（p-c-jun）的表达水平，应用缺口末端标记（TUNEL）法检测海马CA1区神经元凋亡率。结果间歇缺氧组大鼠海马CAl区丙二醛水平为（1．61±0．39）nmol／mg蛋白，显著高于正常对照组的[（1．25±0．29）nmol／mg蛋白]和持续缺氧组的[（1．34±0．24）nmol／mg蛋白]；间歇缺氧组大鼠海马CAl区SOD水平为（45±13）NU／mg蛋白，显著低于正常对照组[（58±12）NU／mg蛋白]和持续缺氧组[（56±10）NU／mg蛋白]；持续缺氧组与正常对照组的差异均无统计学意义。间歇缺氧组p-JNK、p—c-jun表达显著增高，分别是正常对照组的2．1倍及2．3倍；间歇缺氧组海马CA1区神经元凋亡率为（0．30±0．16）％，显著高于正常对照组[（0．12±0．07）％]和持续缺氧组[（0．17±0．09）]。结论间歇缺氧可导致海马CA1区氧化应激状态，从而激活JNK信号传导通路，介导海马神经元凋亡，这可能是阻塞性睡眠呼吸暂停低通气综合征患者神经功能障碍的病理生理基础之一。【     

Mossy fiber-evoked subthreshold responses induce timing-dependent plasticity at hippocampal CA3 recurrent synapses

Dentate granule cells exhibit exceptionally low levels of activity and rarely elicit action potentials in targeted CA3 pyramidal cells. It is thus unclear how such weak input from the granule cells sustains adequate levels of synaptic plasticity in the targeted CA3 network. We report that subthreshold potentials evoked by mossy fibers are sufficient to induce synaptic plasticity between CA3 pyramidal cells, thereby complementing the sparse action potential discharge. Repetitive pairing of a CA3–CA3 recurrent synaptic response with a subsequent subthreshold mossy fiber response induced long-term potentiation at CA3 recurrent synapses in rat hippocampus in vitro. Reversing the timing of the inputs induced long-term depression. The underlying mechanism depends on a passively conducted giant excitatory postsynaptic potential evoked by a mossy fiber that enhances NMDA receptor-mediated current at active CA3 recurrent synapses by relieving magnesium block. The resulting NMDA spike generates a supralinear depolarization that contributes to synaptic plasticity in hippocampal neuronal ensembles implicated in memory.The CA3 area of the hippocampus exhibits a distinctive, highly recurrent circuitry proposed to support autoassociative memory representation (1, 2). This prediction has been confirmed by experimental work demonstrating the pattern completion capabilities of CA3 networks (3), as well as their roles in the spatial tuning of CA1 pyramidal cells, in one-trial contextual learning (4) and in certain forms of memory consolidation (5). CA3 pyramidal cells receive, via the mossy fibers, information processed by granule cells important for both pattern separation (6, 7) and pattern completion functions (7). The faithful transmission of mossy fiber input appears to be ensured by giant synapses composed of presynaptic boutons with up to 45 release sites (8) that target massive spines, the thorny excrescences, on the apical dendrite of CA3 pyramidal cells. Thus, the mossy fiber synapse is often referred to as a detonator synapse (9). In fact, mossy fiber signaling is more compatible with a gatekeeper function than a high-throughput data relay. Although high-frequency bursts of action potentials in a hippocampal granule cell can discharge a targeted CA3 pyramidal cell, the majority of responses evoked by granule cells in CA3 pyramidal cells do not attain the firing threshold (10). Nevertheless, mossy fibers generate powerful signals evoking subthreshold responses that are much larger than typical synaptic events in the brain, with excitatory postsynaptic potentials (EPSPs) and excitatory postsynaptic currents (EPSCs) reaching amplitudes of 10 mV and 1 nA, respectively (11). Here we examined in rat slice cultures how EPSPs generated at mossy fiber synapses are processed in CA3 pyramidal cell dendrites, and evaluated whether subthreshold synaptic responses evoked by mossy fiber stimulation can act as instructive signals to induce plasticity at the pyramidal cell synapses forming the CA3 recurrent network.     

Neuregulin-1 regulates LTP at CA1 hippocampal synapses through activation of dopamine D4 receptors

Neuregulin-1 (NRG-1) is genetically linked with schizophrenia, a neurodevelopmental cognitive disorder characterized by imbalances in glutamatergic and dopaminergic function. NRG-1 regulates numerous neurodevelopmental processes and, in the adult, suppresses or reverses long-term potentiation (LTP) at hippocampal glutamatergic synapses. Here we show that NRG-1 stimulates dopamine release in the hippocampus and reverses early-phase LTP via activation of D4 dopamine receptors (D4R). NRG-1 fails to depotentiate LTP in hippocampal slices treated with the antipsychotic clozapine and other more selective D4R antagonists. Moreover, LTP is not depotentiated in D4R null mice by either NRG-1 or theta-pulse stimuli. Conversely, direct D4R activation mimics NRG-1 and reduces AMPA receptor currents and surface expression. These findings demonstrate that NRG-1 mediates its unique role in counteracting LTP via dopamine signaling and opens future directions to study new aspects of NRG function. The novel functional link between NRG-1, dopamine, and glutamate has important implications for understanding how imbalances in Neuregulin-ErbB signaling can impinge on dopaminergic and glutamatergic function, neurotransmitter pathways associated with schizophrenia.     

Cyclooxygenase-2 inhibition prevents delayed death of CA1 hippocampal neurons following global ischemia

The inducible isoform of the enzyme cyclooxygenase-2 (COX2) is an immediate early gene induced by synaptic activity in the brain. COX2 activity is an important mediator of inflammation, but it is not known whether COX2 activity is pathogenic in brain. To study the role of COX2 activity in ischemic injury in brain, expression of COX2 mRNA and protein and the effect of treatment with a COX2 inhibitor on neuronal survival in a rat model of global ischemia were determined. Expression of both COX2 mRNA and protein was increased after ischemia in CA1 hippocampal neurons before their death. There was increased survival of CA1 neurons in rats treated with the COX2-selective inhibitor SC58125 {1-[(4-methylsulfonyl) phenyl]-3-trifluoro-methyl-5-[(4-fluoro)phenyl] pyrazole} before or after global ischemia compared with vehicle controls. Furthermore, hippocampal prostaglandin E₂ concentrations 24 h after global ischemia were decreased in drug-treated animals compared with vehicle-treated controls. These results suggest that COX2 activity contributes to CA1 neuronal death after global ischemia.     

Synaptic disinhibition during maintenance of long-term potentiation in the CA1 hippocampal subfield.

Long-term potentiation (LTP) in the CA1 region of the hippocampus is widely believed to occur through a strengthening of efficacy of excitatory synapses between afferent fibers and pyramidal cells. An alternative mechanism of LTP, reduction of efficacy of synaptic inhibition, was examined in the present report. The present study demonstrates that the maintenance of LTP in the CA1 hippocampal subfield of guinea pigs is accompanied by impairment of type A gamma-aminobutyric acid (GABA) receptor function, particularly at apical dendritic sites of CA1 pyramidal cells. Enhanced excitability of GABAergic interneurons during LTP represents a strengthening of inhibitory efficacy. The net effect of opposite modifications of synaptic inhibition during LTP of CA1 pyramidal cells is an overall impairment of the strength of GABAergic inhibition, and disinhibition could contribute importantly to CA1 pyramidal cell LTP.     

5-羟色胺在大鼠海马CA1、CA2、CA3脑区的分布与表达

目的通过观察5-羟色胺(5-HT)在海马神经环路的分布和表达,为研究5-HT参与学习记忆的作用机制提供形态学依据。方法采用免疫组织化学技术观测抗5-HT的抗体阳性神经元在海马CA1、CA2和CA3区的分布特征。结果①抗5-HT的抗体在海马CA1、CA2和CA3的细胞中广泛分布。②海马中分子层阳性细胞数较少,排列不规则。锥体层细胞从内到外排列整齐,密集成带,染色强烈。多形层细胞染色细胞散在分布。③空白对照切片未见抗5-HT抗体的阳性神经元胞体。结论 5-HT在大鼠海马分布广泛,可能参与了海马学习记忆有关的过程。     

Enhancement of CA3 hippocampal network activity by activation of group II metabotropic glutamate receptors

Impaired function or expression of group II metabotropic glutamate receptors (mGluRIIs) is observed in brain disorders such as schizophrenia. This class of receptor is thought to modulate activity of neuronal circuits primarily by inhibiting neurotransmitter release. Here, we characterize a postsynaptic excitatory response mediated by somato-dendritic mGluRIIs in hippocampal CA3 pyramidal cells and in stratum oriens interneurons. The specific mGluRII agonists DCG-IV or LCCG-1 induced an inward current blocked by the mGluRII antagonist LY341495. Experiments with transgenic mice revealed a significant reduction of the inward current in mGluR3(-/-) but not in mGluR2(-/-) mice. The excitatory response was associated with periods of synchronized activity at theta frequency. Furthermore, cholinergically induced network oscillations exhibited decreased frequency when mGluRIIs were blocked. Thus, our data indicate that hippocampal responses are modulated not only by presynaptic mGluRIIs that reduce glutamate release but also by postsynaptic mGluRIIs that depolarize neurons and enhance CA3 network activity.     

靶蛋白信号通路相关蛋白在血管性痴呆大鼠海马CA1区的表达

目的观察磷脂酰肌醇3激酶(phosphatidylinositol 3-kinase,PI3K)/蛋白激酶B(protein kinase B,Akt)/哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin,mTOR)信号通路相关蛋白Akt和mTOR在血管性痴呆大鼠海马CA1区的表达及变化情况。方法选择SD大鼠72只,随机分为假手术组、血管性痴呆模型组(模型组)和PI3K抑制剂LY294002组(LY294002组),每组24只。每组又随机分为模型制备成功后1、2、4、8周4个时间点,每个时间点6只。采用改良Pulsinelli四血管阻断法制备血管性痴呆大鼠模型。免疫组织化学法检测Akt、mTOR蛋白的表达情况。结果假手术组海马CA1区不同时间点可见少量Akt和mTOR蛋白阳性表达。与假手术组比较,模型组和LY294002组1、2、4、8周Akt、mTOR蛋白表达明显增高;与模型组比较,LY294002组1、2、4、8周Akt[(8.83±1.47)个/高倍视野vs(12.50±1.87)个/高倍视野,(12.83±2.32)个/高倍视野vs(20.67±4.23)个/高倍视野,(29.00±2.60)个/高倍视野vs(40.33±3.33)个/高倍视野,(24.33±4.32)个/高倍视野vs(35.00±4.15)个/高倍视野]、mTOR蛋白表达明显降低,差异有统计学意义(P<0.05,P<0.01)。结论 Akt和mTOR蛋白在血管性痴呆大鼠海马CA1区过度表达,可能是血管性痴呆发生、发展的重要机制之一。     

Electrophysiological evidence for a hyperpolarizing, galanin (1-15)-selective receptor on hippocampal CA3 pyramidal neurons

The effects of the 29-amino acid neuropeptide galanin [GAL (1-29)], GAL(1-15), GAL(1-16), and the GAL subtype 2 receptor agonist D-tryptophan(2)-GAL(1-29) were studied in the dorsal hippocampus in vitro with intracellular recording techniques. GAL(1-15) induced, in the presence of tetrodotoxin, a dose-dependent hyperpolarization in hippocampal CA3 neurons. Most of the GAL(1-15)-sensitive neurons did not respond to GAL(1-29), GAL(1-16), or D-tryptophan(2)-GAL(1-29). These results indicate the presence of a distinct, yet-to-be cloned GAL(1-15)-selective receptor on CA3 neurons in the dorsal hippocampus.