二甲双胍调节初级视觉皮层兴奋性和抑制性平衡及改善视觉功能的研究（英文）

大脑皮层中兴奋和抑制系统之间的动态平衡决定了皮层神经元对刺激的反应特性.已有研究表明,二甲双胍能够诱导γ-氨基丁酸受体向突触后膜聚集,增强神经系统的抑制效果.本课题进一步探讨了二甲双胍对初级视觉皮层兴奋和抑制系统平衡的调节作用,以及其改善小鼠视觉功能的潜力.实验使用成年雄性小鼠,实验组(metformin) 10只每天给予二甲双胍250 mg/kg,对照组(control) 6只每天给予0.3 ml生理盐水,灌胃处理3周.结果发现二甲双胍可以显著升高囊泡GABA转运蛋白VGAT和突触后抑制性递质受体相关蛋白Gephyrin的合成.此外,它显著降低突触后兴奋性受体Glu A1和Glu N1的表达.多通道电极电生理记录结果显示,二甲双胍作用下小鼠初级视觉皮层的自发放和诱发放显著降低,而信噪比、方向和方位选择性显著增加.实验结果表明,二甲双胍可以通过降低兴奋突触、增强抑制突触,调节初级视皮层的兴奋——抑制平衡,提高信息处理能力,增强视觉功能.     

高糖饮食对青年小鼠初级视觉皮层的功能损伤及其机制

目的 诸多研究证实高糖饮食会对视觉功能造成损伤，但是目前关于高糖饮食对视觉功能影响的研究主要聚焦于视觉通路前端，集中在眼球系统和视神经节部分，对于视觉通路的后端如中枢皮层还未有过相关报道。为了更全面地了解高糖饮食对视觉功能的影响，本文补充高糖饮食对视觉中枢皮层影响的研究。方法 本研究利用GO/NO-GO方位辨别任务的行为学范式、在体多通道电生理技术探究了高糖饮食对青年小鼠初级视觉皮层的影响。结果 行为学结果表明，经历了2个月高糖喂养的青年小鼠，方位辨别能力下降。通过电生理技术分析初级视觉皮层（V1）单个神经元的反应特性，发现高糖饮食小鼠初级视觉皮层单个神经元的方位调谐能力下降，神经元的反应变异性增加、信噪比明显降低。神经元噪音相关性分析结果表明，高糖饮食组小鼠初级视觉皮层的噪音相关性表现出明显的上调。进一步分析群体水平上信噪比和反应变异性的变化，结果表明群体水平上信噪比明显下降而反应变异性明显上升。结论 高糖饮食通过影响初级视觉皮层单个神经元的感受野特征以及群体神经元的信息处理能力，损伤了青年小鼠的方位辨别能力。     

猫初级视皮层内GIu/GABA表达比率的衰老性变化

最近的一些研究结果显示,视皮层内抑制性递质系统作用减弱可能是导致老年性视觉功能衰退的重要因素.是否皮层内兴奋性递质系统亦伴随衰老而发牛改变并影响皮层内神经兴奋与抑制的平衡尚不清楚.为此,利用Nissl染色和免疫组织化学染色方法以及Image-Pro Express图像分析软件对青、老年猫初级视皮层(17区)内各层神经元密度、兴奋性递质谷氨酸免疫反应阳性(Glu-immunoreactive,Glu-IR)神经元密度以及抑制性递质γ-氨基丁酸免疫反应阳性(γ-aminobutyric acid.immunoreactive,GABA-IR)神经元密度进行了统汁分析.结果显示,青、老年猫初级视皮层各层神经元密度均没有明显的年龄性差异(P>0.05);与青年猫相比,老年猫初级视皮层Glu-IR、GABA-IR神经元密度均显著减少(P<0.01),而Glu.IR/GABA.IR神经元密度比率去却显著增大(P<0.01).结果提示,老年猫初级视皮层内兴奋性递质系统作用相对增强,而抑制性递质系统的作用相对减弱,导致皮层内兴奋-抑制平衡关系失调,这可能是引起老年个体视觉功能衰退的重要原因之一.     

猫初级视皮层内Glu/GABA表达比率的衰老性变化(英文）

最近的一些研究结果显示,视皮层内抑制性递质系统作用减弱可能是导致老年性视觉功能衰退的重要因素。是否皮层内兴奋性递质系统亦伴随衰老而发生改变并影响皮层内神经兴奋与抑制的平衡尚不清楚。为此,利用Nissl染色和免疫组织化学染色方法以及Image-Pro Express图像分析软件对青、老年猫初级视皮层(17区)内各层神经元密度、兴奋性递质谷氨酸免疫反应阳性(Glu-immunoreactive, Glu-IR）神经元密度以及抑制性递质γ-氨基丁酸免疫反应阳性(γ-aminobutyric acid-immunoreactive, GABA-IR）神经元密度进行了统计分析。结果显示,青、老年猫初级视皮层各层神经元密度均没有明显的年龄性差异（P>0.05）;与青年猫相比,老年猫初级视皮层Glu-IR、GABA-IR神经元密度均显著减少（P<0.01）,而Glu-IR/GABA-IR神经元密度比率却显著增大（P<0.01）。结果提示,老年猫初级视皮层内兴奋性递质系统作用相对增强,而抑制性递质系统的作用相对减弱,导致皮层内兴奋&#8722;抑制平衡关系失调,这可能是引起老年个体视觉功能衰退的重要原因之一。     

猫初级视皮层内Glu／GABA表达比率的衰老性变化

最近的一些研究结果显示,视皮层内抑制性递质系统作用减弱可能是导致老年性视觉功能衰退的重要因素。是否皮层内兴含性递质系统办伴随衰老而发生改变并影响皮层内神经兴奋与抑制的平衡尚不清楚。为此,利用Nissl染色和免疫组织化学染色方法以及Image—Pro Express图像分析软件对青、老年猫初级视皮层（17区）内各层神经元密度、兴奋性递质谷氦酸免疫反应阳性（Glu—immunoreactive,Glu—IR）神经元密度以及抑制性递质γ-氨基丁酸免疫反应阳性（v．aminobutyric acid-immunoreactive,GABA—IR）神绎元密度进行了统计分析。结果显示,青、老年猫初级视皮层各层神经元密度均没有明显的年龄性差异（P〉0．05）;与青年猫相比,老年猫初级视皮层Glu—IR、GABA．IR神经元密度均显著减少（P〈0．01）,而Glu—IR／GABA-IR神经元密度比率却显著增大（P〈0．01）。结果提示,老年猫初级视皮层内兴奋性递质系统作用相对增强,而抑制性递质系统的作用相对减弱,导致皮层内兴奋-抑制平衡关系失调,这可能是引起老年个体视觉功能衰退的重要原因之一。     

二甲双胍调节初级视觉皮层兴奋性和抑制性平衡及改善视觉功能的研究

大脑皮层中兴奋和抑制系统之间的动态平衡决定了皮层神经元对刺激的反应特性.已有研究表明,二甲双胍能够诱导 γ-氨基丁酸受体向突触后膜聚集,增强神经系统的抑制效果.本课题进一步探讨了二甲双胍对初级视觉皮层兴奋和抑制系统平衡的调节作用,以及其改善小鼠视觉功能的潜力.实验使用成年雄性小鼠,实验组(metformin)10只每天...     

幼年大鼠视皮层神经元对闪光刺激的反应特性

哺乳动物视觉系统的发育延续到出生后,大鼠出生后 3~5 周是视觉系统发育的关键期 . 在关键期中,视皮层的兴奋性和抑制性突触连接逐渐成熟,形成有效的皮层内回路 . 为了观察发育关键期大鼠视皮层神经元的反应特性与成年大鼠的异同,使用胞外单细胞记录的方法对比研究了幼年和成年大鼠对闪光刺激的视觉反应特性 . 结果显示：与成年大鼠相比较,幼年大鼠视皮层神经元对持续闪光刺激显示出更强的适应性,对光刺激的诱发放电频率更低,而在没有光刺激时的自发放电频率更高,从而导致信噪比更低 . 这一结果表明,幼年大鼠视皮层对连续刺激的反应能力下降,对信号的分辨能力也更弱,其原因可能是兴奋性突触和抑制性突触发育的不同步所致 .     

γ-氨基丁酸能抑制可锐化大棕蝠听皮层神经元频率调谐

本实验使用了 9只成年健康的大棕蝠 (Eptesicusfuscus)。采用双声刺激和多管电极电泳导入荷包牡丹碱 (bicuculline,Bic)的方法 ,研究了γ 氨基丁酸 (γ aminobutyricacid ,GABA)能抑制在锐化听皮层 (primaryauditorycortex ,AC ,即初级听皮层 )神经元频率调谐中的作用。结果发现 :正常AC神经元的频率调谐曲线表现出单峰开放式、多峰开放式和单峰封闭式 3种类型 ;用双声刺激方法研究证实 ,至AC神经元的抑制性输入能被抑制性声刺激所激活 ,且这种神经抑制有自身的最佳频率 ,根据其对兴奋反应的影响程度和系统地改变抑制性声刺激的强度 ,可在兴奋性频率调谐曲线或兴奋区的高频边或 /和低频边测出抑制性频率调谐曲线或抑制区 ;当这种抑制性输入被抑制性声刺激激活后 ,能降低阈上 10dB声强引起的兴奋反应的发放率 ,抑制效率随抑制声刺激强度的增强而加强 ;电泳GABAa受体拮抗剂荷包牡丹碱Bic后 ,可不同程度地去GABA能抑制 ,扩宽频率调谐曲线 ,使多峰调谐曲线变成单峰 ,封闭型变成开放型。表明GABA能抑制参与构成至AC神经元的抑制性输入 ,在正常情况下这种抑制有助于提高中枢听神经元的信号 /噪声比和频率分析能力 ,并锐化频率调谐。因此本结果提示 ,声音的各参量中所包含的信息从外周传入中枢后 ,随着中枢的升     

miR-34a敲除对小鼠大脑发育和行为的影响

miR-34a是一种进化保守并在脑中高表达的miRNA,已有研究显示其可能参与调控神经干细胞增殖和分化、神经元成熟和凋亡、恐惧记忆巩固等脑发育和功能的多个重要方面,但内源性miR-34a缺失是否显著影响脑正常发育和功能尚属未知。在本研究中,我们对miR-34a全敲除小鼠模型进行检测,发现miR-34a的缺失不影响成年鼠脑的重量、基本结构、大脑皮层的分层及其中几类主要类型的兴奋性和抑制性神经元的数量和分布,也不影响恐惧记忆的巩固及焦虑和抑郁样行为,但对小鼠的运动协调能力有一定影响。由于miR-34a在大脑皮层小清蛋白(parvalbumin,PV)亚型抑制性神经元中特异高表达,我们利用PV-Cre对miR-34a进行了条件敲除,但并未观察到这类神经元数量与分布的改变。我们的研究证明,miR-34a虽然参与调控小鼠大脑发育和行为的特定方面,但并非是调控大脑结构分区与皮层分层形成、皮层主要神经元类型产生与维持、恐惧记忆形成与巩固所必需的关键因子。     

胃动素对大鼠下丘脑胃牵张敏感神经元和胃运动的影响(英文)

目的:研究胃动素对下丘脑弓状核胃牵张敏感神经元放电活动和胃运动的影响。方法:采用4管玻璃微电极细胞外记录胃动素对大鼠弓状核胃牵张敏感神经元活动,采用胃内置传感器观察胃动素对对清醒大鼠胃运动的影响。结果:65.5%的弓状核神经元为胃扩张敏感性神经元,其中55.6%为胃扩张兴奋性神经元,44.4%为抑制性神经元。胃扩张刺激后兴奋性神经元的放电频率显著增加(P<0.01),而抑制性神经元的放电频率显著降低(P<0.01)。弓状核内微量注射胃动素,70%的兴奋性神经元在胃扩张刺激后表现为兴奋作用,17.5%的神经元表现为抑制作用,并且放电频率显著增加(P<0.05)。同样,在抑制性神经元中,65.6%在注射胃动素后引起电活动增强,放电频率显著降低(P<0.05)。而胃动素受体拮抗剂GM-109可以完全阻断这种由胃动素诱导的兴奋作用,提示,胃动素在弓状核通过其特异性受体调控神经元活动。在胃运动实验中,弓状核微量注射胃动素后,胃运动的收缩频率和幅度都显著增加(P<0.05);同时,这种兴奋作用也可被GM-109阻断。结论:研究证实了弓状核胃动素神经元接收来自胃感受器的外周躯体感觉传入神经的冲动,并通过某些下级核团通路发挥...     

Preserved Excitatory-Inhibitory Balance of Cortical Synaptic Inputs following Deprived Eye Stimulation after a Saturating Period of Monocular Deprivation in Rats

Monocular deprivation (MD) during development leads to a dramatic loss of responsiveness through the deprived eye in primary visual cortical neurons, and to degraded spatial vision (amblyopia) in all species tested so far, including rodents. Such loss of responsiveness is accompanied since the beginning by a decreased excitatory drive from the thalamo-cortical inputs. However, in the thalamorecipient layer 4, inhibitory interneurons are initially unaffected by MD and their synapses onto pyramidal cells potentiate. It remains controversial whether ocular dominance plasticity similarly or differentially affects the excitatory and inhibitory synaptic conductances driven by visual stimulation of the deprived eye and impinging onto visual cortical pyramids, after a saturating period of MD. To address this issue, we isolated visually-driven excitatory and inhibitory conductances by in vivo whole-cell recordings from layer 4 regular-spiking neurons in the primary visual cortex (V1) of juvenile rats. We found that a saturating period of MD comparably reduced visually–driven excitatory and inhibitory conductances driven by visual stimulation of the deprived eye. Also, the excitatory and inhibitory conductances underlying the synaptic responses driven by the ipsilateral, left open eye were similarly potentiated compared to controls. Multiunit recordings in layer 4 followed by spike sorting indicated that the suprathreshold loss of responsiveness and the MD-driven ocular preference shifts were similar for narrow spiking, putative inhibitory neurons and broad spiking, putative excitatory neurons. Thus, by the time the plastic response has reached a plateau, inhibitory circuits adjust to preserve the normal balance between excitation and inhibition in the cortical network of the main thalamorecipient layer.     

Synaptotagmin-2 is a reliable marker for parvalbumin positive inhibitory boutons in the mouse visual cortex

Background

Inhibitory innervation by parvalbumin (PV) expressing interneurons has been implicated in the onset of the sensitive period of visual plasticity. Immunohistochemical analysis of the development and plasticity of these inhibitory inputs is difficult because PV expression is low in young animals and strongly influenced by neuronal activity. Moreover, the synaptic boutons that PV neurons form onto each other cannot be distinguished from the innervated cell bodies by immunostaining for this protein because it is present throughout the cells. These problems call for the availability of a synaptic, activity-independent marker for PV+ inhibitory boutons that is expressed before sensitive period onset. We investigated whether synaptotagmin-2 (Syt2) fulfills these properties in the visual cortex. Syt2 is a synaptic vesicle protein involved in fast Ca²⁺ dependent neurotransmitter release. Its mRNA expression follows a pattern similar to that of PV throughout the brain and is present in 30–40% of hippocampal PV expressing basket cells. Up to now, no quantitative analyses of Syt2 expression in the visual cortex have been carried out.

Methodology/Principal Findings

We used immunohistochemistry to analyze colocalization of Syt2 with multiple interneuron markers including vesicular GABA transporter VGAT, calbindin, calretinin, somatostatin and PV in the primary visual cortex of mice during development and after dark-rearing.

Conclusions/Significance

We show that in the adult visual cortex Syt2 is only found in inhibitory, VGAT positive boutons. Practically all Syt2 positive boutons also contain PV and vice versa. During development, Syt2 expression can be detected in synaptic boutons prior to PV and in contrast to PV expression, Syt2 is not down-regulated by dark-rearing. These properties of Syt2 make it an excellent marker for analyzing the development and plasticity of perisomatic inhibitory innervations onto both excitatory and inhibitory neurons in the visual cortex.     

Brain-derived neurotrophic factor selectively regulates dendritogenesis of parvalbumin-containing interneurons in the main olfactory bulb through the PLCgamma pathway

Molecular mechanisms of neurotrophin signaling on dendrite development and dynamics are only partly understood. To address the role of brain-derived neurotrophic factor (BDNF) in the morphogenesis of GABAergic neurons of the main olfactory bulb, we analyzed mice lacking BDNF, mice carrying neurotrophin-3 (NT3) in the place of BDNF, and TrkB signaling mutant mice with a receptor that can activate phospholipase Cgamma (PLCgamma) but is unable to recruit the adaptors Shc/Frs2. BDNF deletion yielded a compressed olfactory bulb with a significant loss of parvalbumin (PV) immunoreactivity in GABAergic interneurons of the external plexiform layer. Dendrite development of PV-positive interneurons was selectively attenuated by BDNF since other Ca2+ -binding protein-containing neuron populations appeared unaffected. The deficit in PV-positive neurons could be rescued by the NT3/NT3 alleles. The degree of PV immunoreactivity was dependent on BDNF and TrkB recruitment of the adaptor proteins Shc/Frs2. In contrast, PLCgamma signaling from the TrkB receptor was sufficient for dendrite growth in vivo and consistently, blocking PLCgamma prevented BDNF-dependent dendrite development in vitro. Collectively, our results provide genetic evidence that BDNF and TrkB signaling selectively regulate PV expression and dendrite growth in a subset of neurochemically-defined GABAergic interneurons via activation of the PLCgamma pathway.     

Brain‐derived neurotrophic factor selectively regulates dendritogenesis of parvalbumin‐containing interneurons in the main olfactory bulb through the PLCγ pathway

Molecular mechanisms of neurotrophin signaling on dendrite development and dynamics are only partly understood. To address the role of brain‐derived neurotrophic factor (BDNF) in the morphogenesis of GABAergic neurons of the main olfactory bulb, we analyzed mice lacking BDNF, mice carrying neurotrophin‐3 (NT3) in the place of BDNF, and TrkB signaling mutant mice with a receptor that can activate phospholipase Cγ (PLCγ) but is unable to recruit the adaptors Shc/Frs2. BDNF deletion yielded a compressed olfactory bulb with a significant loss of parvalbumin (PV) immunoreactivity in GABAergic interneurons of the external plexiform layer. Dendrite development of PV‐positive interneurons was selectively attenuated by BDNF since other Ca²⁺‐binding protein‐containing neuron populations appeared unaffected. The deficit in PV‐positive neurons could be rescued by the NT3/NT3 alleles. The degree of PV immunoreactivity was dependent on BDNF and TrkB recruitment of the adaptor proteins Shc/Frs2. In contrast, PLCγ signaling from the TrkB receptor was sufficient for dendrite growth in vivo and consistently, blocking PLCγ prevented BDNF‐dependent dendrite development in vitro. Collectively, our results provide genetic evidence that BDNF and TrkB signaling selectively regulate PV expression and dendrite growth in a subset of neurochemically‐defined GABAergic interneurons via activation of the PLCγ pathway. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Sound-driven synaptic inhibition in primary visual cortex

Multimodal objects and events activate many sensory cortical areas simultaneously. This is possibly reflected in reciprocal modulations of neuronal activity, even at the level of primary cortical areas. However, the synaptic character of these interareal interactions, and their impact on synaptic and behavioral sensory responses are unclear. Here, we found that activation of auditory cortex by a noise burst drove local GABAergic inhibition on supragranular pyramids of the mouse primary visual cortex, via cortico-cortical connections. This inhibition was generated by sound-driven excitation of a limited number of cells in infragranular visual cortical neurons. Consequently, visually driven synaptic and spike responses were reduced upon bimodal stimulation. Also, acoustic stimulation suppressed conditioned behavioral responses to a dim flash, an effect that was prevented by acute blockade of GABAergic transmission in visual cortex. Thus, auditory cortex activation by salient stimuli degrades potentially distracting sensory processing in visual cortex by recruiting local, translaminar, inhibitory circuits.     

Spatiotemporal properties of the action potential propagation in the mouse visual cortical slice analyzed by calcium imaging

The calcium ion (Ca(2+)) is an important messenger for signal transduction, and the intracellular Ca(2+) concentration ([Ca(2+)](i)) changes in response to an excitation of the cell. To reveal the spatiotemporal properties of the propagation of an excitatory signal with action potentials in the primary visual cortical circuit, we conducted a Ca(2+) imaging study on slices of the mouse visual cortex. Electrical stimulation of layer 4 evoked [Ca(2+)](i) transients around the stimulus electrode. Subsequently, the high [Ca(2+)](i) region mainly propagated perpendicular to the cortical layer (vertical propagation), with horizontal propagation being restricted. When the excitatory synaptic transmission was blocked, only weak and concentric [Ca(2+)](i) transients were observed. When the action potential was blocked, the [Ca(2+)](i) transients disappeared almost completely. These results suggested that the action potential contributed to the induction of the [Ca(2+)](i) transients, and that excitatory synaptic connections were involved in the propagation of the high [Ca(2+)](i) region in the primary visual cortical circuit. To elucidate the involvement of inhibitory synaptic connections in signal propagation in the primary visual cortex, the GABA(A) receptor inhibitor bicuculline was applied. In this case, the evoked signal propagated from layer 4 to the entire field of view, and the prolonged [Ca(2+)](i) transients were observed compared with the control condition. Our results suggest that excitatory neurons are widely connected to each other over the entire primary visual cortex with recurrent synapses, and inhibitory neurons play a fundamental role in the organization of functional sub-networks by restricting the propagation of excitation signals.     

Increased Cortical Inhibition in Autism-Linked Neuroligin-3R451C Mice Is Due in Part to Loss of Endocannabinoid Signaling

A single, maternally inherited, X-linked point mutation leading to an arginine to cysteine substitution at amino acid 451 (R451C) of Neuroligin 3 (NLGN3^R451C) is a likely cause of autism in two brothers. Knockin mice expressing the Nlgn3^R451C mutation in place of wild-type Nlgn3 demonstrate increased inhibitory synaptic strength in somatosensory cortex, resulting in an excitatory/inhibitory (E/I) imbalance that is potentially relevant for autism-associated behavioral deficits characteristic of these mice. We have replicated the increase in evoked inhibitory postsynaptic currents (eIPSCs) onto layer II/III cortical pyramidal neurons. We also find that increased frequency of spontaneous mIPSCs in Nlgn3^R451C mice occurs in the absence of action potential-driven transmission. This suggests the E/I imbalance is due to changes at the synapse level, as opposed to the network level. Next, we use paired whole-cell recordings in an attempt to identify specific interneuron subtypes affected by the Nlgn3^R451C mutation. Curiously, we observe no change in the amplitude of cell-to-cell, unitary IPSCs (uIPSCs) from parvalbumin-positive (PV) or somatostatin-positive (SOM) interneurons onto pyramidal neurons. We also observe no change in the number or density of PV and SOM interneurons in LII/III of somatosensory cortex. This effectively rules out a role for these particular interneurons in the increased inhibitory synaptic transmission, pointing to perhaps alternative interneuron subtypes. Lastly, impaired endocannabinoid signaling has been implicated in hippocampal synaptic dysfunction in Nlgn3^R451C mice, but has not been investigated at cortical synapses. We find that bath application of the CB1 antagonist, AM 251 in WT mice eliminates the Nlgn3^R451C increase in eIPSC amplitude and mIPSC frequency, indicating that increased inhibitory transmission in mutant mice is due, at least in part, to a loss of endocannabinoid signaling through CB1 receptors likely acting at interneurons other than PV or SOM.