GABAB-receptor-activated K+ current in voltage-clamped CA3 pyramidal cells in hippocampal cultures.

GABAB receptors are a subclass of receptors for gamma-amino-n-butyric acid (GABA) that are also activated by the antispastic drug beta-p-chlorophenyl-GABA (baclofen). One effect of baclofen is to inhibit excitatory transmission from CA3 to CA1 hippocampal pyramidal cells. To identify the ionic mechanism of GABAB-receptor-mediated depression, we have studied the effect of baclofen and GABA on ionic currents in voltage-clamped CA3 pyramidal cell somata in rat hippocampal slice cultures. Baclofen (10 microM) induced an inwardly rectifying outward current that reversed at -74 +/- 4.3 mV (mean +/- SD). This appeared to be a K+ current since (i) its reversal potential showed the expected shift when extracellular K+ concentration was changed and (ii) it was blocked by external Ba2+ or internal Cs+. The action of baclofen was closely imitated by GABA after the GABAA-mediated Cl- current had been abolished with pitrazepin (10 microM); under these conditions, GABA (100 microM) also produced an inwardly rectifying, Ba2+-sensitive current with a reversal potential identical to that of the baclofen-induced current. When outward currents were blocked with internal Cs+, the residual inward voltage-dependent Ca2+ current was not changed by baclofen. It is concluded that the primary effect of GABAB-receptor activation in these neurones is to increase K+ permeability rather than to reduce Ca2+ permeability.     

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.     

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.     

Selective estrogen receptor modulators regulate phasic activation of hippocampal CA1 pyramidal cells by estrogen

Previous studies demonstrated that estrogen induces two sequential waves of CA1 pyramidal cell activation, evidenced by induction of c-Fos at 2 and 24 h after a single estrogen treatment. The second wave of activation is paralleled by suppression of immunoreactivity for glutamic acid decarboxylase-65kD (GAD65) in CA1 and decreased synaptic inhibition of CA1 pyramidal cells. Here, we report that pretreatment with either of the selective estrogen receptor (ER) modulators, tamoxifen (T) or CI628, has no effect on the first wave of c-Fos expression at 2 h but completely blocks the second wave of c-Fos and the suppression of GAD65 at 24 h. Interestingly, T, given 4 h after estrogen, failed to block c-Fos expression or suppression of GAD65 at 24 h. Electrophysiological experiments showed that the T metabolite, 4OH-T, or CI628 can inhibit the so-called rapid estrogen effect, to potentiate excitatory postsynaptic currents (EPSCs) in CA1 pyramidal cells. Thus, estrogen seems to act within 4 h via classical ERs and/or a rapid estrogen effect, such as EPSC potentiation, to produce activation/disinhibition of pyramidal cells 24 h later. In contrast, the initial activation of pyramidal cells, at 2 h after estrogen, seems to involve neither classical ERs nor rapid potentiation of EPSCs.     

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.     

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。     

An increase in dendritic spine density on hippocampal CA1 pyramidal cells following spatial learning in adult rats suggests the formation of new synapses.

The search for cellular correlates of learning is a major challenge in neurobiology. The hippocampal formation is important for learning spatial relations. A possible long-lasting consequence of such spatial learning is alteration of the size, shape, or number of excitatory synapses. The dendritic spine density is a good index for the number of hippocampal excitatory synapses. By using laser-scanning confocal microscopy, we observed a significantly increased spine density in CA1 basal dendrites of spatially trained rats when compared to nontrained controls. With unchanged dendritic length, the higher spine density reflects an increased number of excitatory synapses per neuron associated with spatial learning.     

Stress-induced alterations in hippocampal plasticity, place cells, and spatial memory

Acute, inescapable, and unpredictable stress can profoundly modify brain and cognition in humans and animals. The present study investigated the ensuing effects of 2-h variable "audiogenic" stress on three related levels of hippocampal functions in rats: long-term potentiation, place cell activity, and spatial memory. In agreement with prior findings, we observed that stress reduced the magnitude of Schaffer collateral/commissural-Cornu Ammonis field 1 long-term potentiation in vitro, and selectively impaired spatial memory on a hidden platform version of the Morris water maze task. We also observed that stress impaired the stability of firing rates (but not firing locations) of place cells recorded from dorsal Cornu Ammonis field 1 in rats foraging freely on a novel open-field platform located in a familiar surrounding room. These findings suggest that stress-induced modifications in synaptic plasticity may prevent the storage of stable "rate maps" by hippocampal place cells, which in turn may contribute to spatial memory impairments associated with stress.     

天麻乙酸乙酯提取物对血管性痴呆大鼠海马CA1区锥体细胞的影响

目的观察天麻乙酸乙酯提取物对血管性痴呆模型大鼠海马CA1区锥体细胞的影响。方法采用双侧颈总动脉永久性结扎法,造成慢性脑灌注不足所致SD大鼠血管性痴呆模型。造模6周后,40只大鼠随机分为5组,假手术组、模型组、尼莫地平组、天麻乙酸乙酯提取物高剂量组(高剂量组)和天麻乙酸乙酯提取物低剂量组(低剂量组),每组8只。给药3周后,HE染色检测海马锥体细胞的变化。结果与假手术组比较,模型组大鼠海马CA1区锥体细胞数目明显减少(P<0.01);与模型组比较,尼莫地平组和高剂量组大鼠海马CA1区锥体细胞数目明显增多(P<0.01),低剂量组大鼠海马CA1区锥体细胞数目无明显变化(P>0.05)。结论天麻乙酸乙酯提取物能改善血管性痴呆大鼠脑组织海马CA1区锥体细胞的病理改变。     

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.     

Topographic specificity of functional connections from hippocampal CA3 to CA1

The hippocampus is a cortical region thought to play an important role in learning and memory. Most of our knowledge about the detailed organization of hippocampal circuitry responsible for these functions is derived from anatomical studies. These studies present an incomplete picture, however, because the functional character and importance of connections are often not revealed by anatomy. Here, we used a physiological method (photostimulation with caged glutamate) to probe the fine pattern of functional connectivity between the CA3 and CA1 subfields in the mouse hippocampal slice preparation. We recorded intracellularly from CA1 and CA3 pyramidal neurons while scanning with photostimulation across the entire CA3 subfield with high spatial resolution. Our results show that, at a given septotemporal level, nearby CA1 neurons receive synaptic inputs from neighboring CA3 neurons. Thus, the CA3 to CA1 mapping preserves neighbor relations.     

Existence of nitric oxide synthase in rat hippocampal pyramidal cells.

It has been proposed that nitric oxide (NO) serves as a key retrograde messenger during long-term potentiation at hippocampal synapses, linking induction of long-term potentiation in postsynaptic CA1 pyramidal cells to expression of long-term potentiation in presynaptic nerve terminals. However, nitric oxide synthase (NOS), the proposed NO-generating enzyme, has not yet been detected in the appropriate postsynaptic cells. We here demonstrate specific NOS immunoreactivity in the CA1 region of hippocampal sections by using an antibody specific for NOS type I and relatively gentle methods of fixation. NOS immunoreactivity was found in dendrites and cell bodies of CA1 pyramidal neurons. Cultured hippocampal pyramidal cells also displayed specific immunostaining. Control experiments showed no staining with preimmune serum or immune serum that was blocked with purified NOS. These results demonstrate that CA1 pyramidal cells contain NOS, as required were NO involved in retrograde signaling during hippocampal synaptic plasticity.     

Bidirectional plasticity of excitatory postsynaptic potential (EPSP)-spike coupling in CA1 hippocampal pyramidal neurons

Integration of synaptic excitation to generate an action potential (excitatory postsynaptic potential-spike coupling or E-S coupling) determines the neuronal output. Bidirectional synaptic plasticity is well established in the hippocampus, but whether active synaptic integration can display potentiation and depression remains unclear. We show here that synaptic depression is associated with an N-methyl-d-aspartate receptor-dependent and long-lasting depression of E-S coupling. E-S depression is input-specific and is expressed in the presence of gamma-aminobutyric acid type A and B receptor antagonists. In single neurons, E-S depression is observed without modification of postsynaptic passive properties. We conclude that a decrease in intrinsic excitability underlies E-S depression and is synergic with glutamatergic long-term depression.     

CA3 size predicts the precision of memory recall

There is enduring interest in why some of us have clearer memories than others, given the substantial individual variation that exists in retrieval ability and the precision with which we can differentiate past experiences. Here we report novel evidence showing that variation in the size of human hippocampal subfield CA3 predicted the amount of neural interference between episodic memories within CA3, which in turn predicted how much retrieval confusion occurred between past memories. This effect was not apparent in other hippocampal subfields. This shows that subtle individual differences in subjective mnemonic experience can be accurately gauged from measurable variations in the anatomy and neural coding of hippocampal region CA3. Moreover, this mechanism may be relevant for understanding memory muddles in aging and pathological states.Our memories often contain overlapping elements, because they tend to feature the same people and places that form the cornerstones of our lives. Nevertheless, we are generally able to recall many of these past experiences as distinct episodes, although we are not all equally adept at doing so. There is substantial individual variation in retrieval ability and the precision with which we can differentiate past events (1, 2). This is most acute as we age and in conditions such as dementia, where confusion about the past is often evident (2). There is keen interest, therefore, in elucidating the neural mechanisms that allow us to recollect numerous life experiences despite a high degree of intermemory similarity.We know little about how this is achieved in humans, but theoretical models propose that computations within hippocampal subfields facilitate the efficient storage and retrieval of similar memories (3–7). When we experience an event, pattern separation leads to the formation of a distinct neural representation within region CA3 (8–11). At retrieval, a previously stored memory representation within CA3 can be reactivated through the process of pattern completion (12, 13). However, when episodes are highly similar, the CA3 neuronal representations may not be completely distinct, leading to partial overlap (14). It is therefore not clear precisely what the limits of CA3 pattern separation might be. Here we directly tested the capacity of human CA3 to maintain distinct episodic representations in the presence of overlapping elements. We further investigated whether variation in this ability provides an explanatory account of individual differences in the precision of episodic memory retrieval.     

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。     

Involvement of ryanodine receptors in neurotrophin-induced hippocampal synaptic plasticity and spatial memory formation

Ryanodine receptors (RyR) amplify activity-dependent calcium influx via calcium-induced calcium release. Calcium signals trigger postsynaptic pathways in hippocampal neurons that underlie synaptic plasticity, learning, and memory. Recent evidence supports a role of the RyR2 and RyR3 isoforms in these processes. Along with calcium signals, brain-derived neurotrophic factor (BDNF) is a key signaling molecule for hippocampal synaptic plasticity and spatial memory. Upon binding to specific TrkB receptors, BDNF initiates complex signaling pathways that modify synaptic structure and function. Here, we show that BDNF-induced remodeling of hippocampal dendritic spines required functional RyR. Additionally, incubation with BDNF enhanced the expression of RyR2, RyR3, and PKMζ, an atypical protein kinase C isoform with key roles in hippocampal memory consolidation. Consistent with their increased RyR protein content, BDNF-treated neurons generated larger RyR-mediated calcium signals than controls. Selective inhibition of RyR-mediated calcium release with inhibitory ryanodine concentrations prevented the PKMζ, RyR2, and RyR3 protein content enhancement induced by BDNF. Intrahippocampal injection of BDNF or training rats in a spatial memory task enhanced PKMζ, RyR2, RyR3, and BDNF hippocampal protein content, while injection of ryanodine at concentrations that stimulate RyR-mediated calcium release improved spatial memory learning and enhanced memory consolidation. We propose that RyR-generated calcium signals are key features of the complex neuronal plasticity processes induced by BDNF, which include increased expression of RyR2, RyR3, and PKMζ and the spine remodeling required for spatial memory formation.     

Differential distribution of NCX1 contributes to spine-dendrite compartmentalization in CA1 pyramidal cells

Compartmentalization of Ca(2+) between dendritic spines and shafts is governed by diffusion barriers and a range of Ca(2+) extrusion mechanisms. The distinct contribution of different Ca(2+) clearance systems to Ca(2+) compartmentalization in dendritic spines versus shafts remains elusive. We applied a combination of ultrastructural and functional imaging methods to assess the subcellular distribution and role of NCX1 in rat CA1 pyramidal cells. Quantitative electron microscopic analysis of preembedding immunogold reactions revealed uniform densities of NCX1 along the shafts of apical and basal dendrites, but densities in dendritic shafts were approximately seven times higher than in dendritic spines. In line with these results, two-photon imaging of synaptically activated Ca(2+) transients during NCX blockade showed preferential action localized to the dendritic shafts for NCXs in regulating spine-dendrite coupling.     

Inhibition of dendritic spine induction on hippocampal CA1 pyramidal neurons by a nonsteroidal estrogen antagonist in female rats

Estrogens regulate the formation of excitatory synaptic connections in the hippocampus of female rats. Because the adult hippocampus has a very low concentration of intracellular estrogen receptors, it is unclear whether a conventional genomic mechanism is involved. Nonsteroidal estrogen antagonists are useful tools to study estrogen action because they can provide pharmacological data in favor of a particular pathway of estrogen action and evidence against other pathways. To investigate the role of intracellular estrogen receptors in the estrogen induction of synapse formation, we took advantage of previous studies in which we had shown that an estrogen antagonist, CI-628, enters the brain and blocks estrogen induction of progestin receptors to study whether the same antagonist would either mimic or block effects of estradiol to induce excitatory spine synapses. Using silver impregnation of neurons by the single section Golgi technique and morphometric analysis, we found that CI-628 effectively prevented estrogen induction of spines on CA1 pyramidal neurons, without having any agonist effects of its own. This result is consistent with an action of estradiol via intracellular estrogen receptors that are known to be expressed by interneurons within the hippocampus.     

局灶性脑缺血大鼠海马CA3区BDNF的动态表达

目的　研究局灶性脑缺血损伤后海马 CA3区 BDNF的动态表达以及神经修复的可塑性。方法　选取健康成年 SD大鼠 40只 ,随机分为脑缺血组和对照组。采用线栓法建立大脑中动脉脑缺血大鼠模型 ,应用免疫组化技术观察海马 CA3区 BDNF的表达。结果　脑缺血后海马 CA3区 BDNF的表达 7d时开始升高 ,1 4 d时明显增多 ,2 1 d时达到高峰 (P<0 .0 1 ) ,以后逐渐降低。结论　脑缺血损伤后中枢神经系统具有再生和修复的可塑性。