视网膜双极细胞的突触传递

双极细胞是视网膜中处于信号传递的直接通路中的中间神经元,以带型突触传递由分级电位编码的视觉信号。近年来,应用膜电容测定、钙光成像等技术,对双极细胞递质释放的特点及动力学特性进行了细致的研究,不仅有助于阐明这些细胞独特的生理功能,也对了解以带型突触传递信号的感觉神经元的功能特性提供了启示。     

视网膜双极细胞上的谷氨酸受体

脊椎动物视网膜双极细胞有ＯＮ型和ＯＦＦ型两类：ＯＮ型双极细胞对光反应为去极化,ＯＦＦ型双极细胞对光反应为超极化。现知,ＯＮ型双极细胞上含有代谢型谷氨酸受体,暗中光感受器细胞持续释放的谷所酸与之结合后,造成阳离子通道关闭,引起细胞超极化;光照时谷氨酸释放减少,引起去极化。而ＯＦＦ型双极细胞上含有离子型谷氨酸受体,谷氨酸与之结合后受体本身通道打开,引起细胞去极化;光照时,谷氨酸释放减少,引起超极化。     

鲫鱼视网膜双极细胞上GABAC和GABAA受体的动力学差异

用全细胞模式的膜片钳技术研究了鲫鱼视网膜双极细胞上的GABAC和GABAA受体激活(activation)、失敏(desensitization)和失活(deactivation)等动力学特性.研究表明GABAC受体的反应动力学一般慢于GABAA受体.两者的激活动力学可用单指数函数很好拟合,GABAC受体的拟合时间常数(τ)为44.57 ms,而GABAA受体的平均时间常数是10.86 ms.再者,GABAA受体的失敏具有快、慢两个成分,其时间常数分别是ιfast=2.16 s和τslow=19.78 s,而GABAC的失敏则遵从单指数规律,时间常数为6.98 s.两种受体的失活均能为双指数函数拟合,其中GABAC受体的时间常数(ιfast=674.8 ms,τslow=2090ms)远大于GABAA受体的(ιfast=42.07 ms,ιslow=275.1 ms).这些动力学特性的差异提示,GABAC和GABAA受体可能在不同的频域参与视网膜的信号处理.     

NO对鲫鱼视网膜视杆和视锥信号传递的不同作用

在离体、灌流的鲫鱼视网膜上,考察了一氧化氮(NO)对视网膜电图(ERG)和水平细胞的作用.NO的供体硝普钠(SNP)压抑暗视ERGb波,却增大明视b波,这些作用均可为血红蛋白所阻遏.进而,SNP使视杆水平细胞对光反应减小,而增强L型视锥水平细胞的对光反应.这些结果表明,NO在外视网膜可压抑视杆系统的活动而增强视锥系统的活动.此外,可溶性鸟苷酸环化酶的抑制剂亚甲基蓝对视杆、视锥水平细胞的作用恰与SNP作用相反,这提示NO的作用可能由cGMP所介导.对NO的作用位点提出了工作假设.     

GABA对鲫鱼视网膜视锥水平细胞的选择性压抑

本工作应用细胞内记录技术,在灌流的鲫鱼视网膜的标本上,研究了γ－氨基丁酸对视杆水平细胞笔视锥水平细胞的影响。结果表明,在ＧＡＢＡ的作用下,Ｌ型视锥水平细胞暗中膜电位超极化,对光反应减小;ＧＡＢＡＡ受体的特异性拮抗剂荷包牡丹碱在７０％的细胞上能阻断上述ＧＡＢＡ的效应。     

鲫鱼视网膜亮度型水平细胞上不同视锥信号的相互作用:实验及模型

本文应用胞内记录和动态模型分析方法,研究了离体鲫鱼视网膜视锥驱动的高度型水平细胞（ＬＨＣ）上不同视锥信号的相互作用。实验表明,绿背景光的作用可以提高ＬＨＣ的红光反应,这种增强作用与绿敏锥的活动程度密切相关,模型分析表明,背景光 的作用谷氨酸介导的前馈性通路和ＧＡＢＡ介导的反馈性通路活动同时得以增强,水平细胞对光反应的增强效应不能为外泊性ＧＡＢＡ所消除。则其程度为前馈性通路和反馈性通路活动增加的相对     

多巴胺对鲫鱼视网膜H1型水平细胞上电压门控钙离子通道的调控特性

利用细胞内的钙离子成像技术,研究了多巴胺对鲫鱼视网膜H1型水平细胞上L型电压门控钙离子通道的调控特性。研究发现,在不同胞外pH(6.8、7.4、8.0)条件下,不同浓度多巴胺(50和500μmol/L、1 mmol/L)对L型电压门控钙离子通道均具有上调作用。50μmol/L多巴胺在不同pH下的上调程度没有显著性差异;高浓度多巴胺(500μmol/L和1 mmol/L)在pH8.0条件下比pH6.8和7.4条件下具有更显著的上调作用。这些结果表明,在鲫鱼视网膜H1型水平细胞上,多巴胺对电压门控钙离子通道的调控与胞外pH环境密切相关。在光照情况下,L型电压门控钙离子通道活性被相对高浓度多巴胺上调,并被胞外碱性环境协同增强。这种协同增强效应有助于阐明视网膜对光反应的信息传递机制。     

低钙对鲫鱼视网膜中视杆,视锥信号向水平细胞传递的不同作用

本工作应用细胞内记录技术,在灌流的鲫鱼离体视网膜的标本上,研究了低钙对外网状层中视锥、视杆信号向水平细胞传递的不同影响。当降低灌流溶液中Ｃａ（２＋）浓度至０．１ｍｍｏｌ／Ｌ时使视锥－和视杆－水平细胞（Ｃｏｎｅ－ＨＣ和Ｒｏｄ－ＨＣ）均去极化,但对两者的光反应性有不同的影响：使Ｌ型Ｃｏｎｅ－ＨＣ对６８０ｕｍ和５００ｕｍ闪光反应的幅度有不同程度的减小,但使Ｒｏｄ－ＨＣ对光反应的幅度显著增大。在０．１ｍｍｏｌ／ＬＣａ（２＋）Ｒｉｎｇｅｒ液灌流时,无论是明视ＰⅢ（反映机锥活动）或暗视ＰⅢ（反映视杆活动）,其反应的幅度均增大,提示发生在低钙时Ｃｏｎｅ－ＨＣ和Ｒｏｄ－ＨＣ光反应性的不同变化产生于突触传递的过程中。进而,磷酸二酯酶抑制剂ＩＢＭＸ对ＰⅢ的影响与０．１ｍｍｏｌ／ＬＣａ（２＋）Ｒｉｎｇｅｒ液的作用相似,而对Ｌ型Ｃｏｎｅ－ＨＣ和Ｒｏｄ－ＨＣ的作用均是使光反应性增大。这提示,在０．１ｍｍｏｌ／ＬＣａ（２＋）的Ｒｉｎｇｅｒ液中,Ｃｏｎｅ－ＨＣ和Ｒｏｄ－ＨＣ光反应性的变化差异可能是由于低钙对视锥和视杆终末Ｃａ２＋内流的不同影响而产生。     

AMPA对视网膜L型水平细胞所接收的红、绿敏视锥信号的不同调制作用

在离体灌流的鲫鱼视网膜,应用细胞内记录技术,研究了谷氨酸受体激动剂——AMPA对L型水平细胞(LHC)的作用.AMPA压抑LHC由红敏视锥驱动的反应,却增强由绿敏视锥驱动的反应.此效应可为AMPA受体特异的拮抗剂(GYKI53655)所逆转,表明仅有AMPA受体参与其中.印防己毒素(PTX)或双氢红藻氨酸(DHK)存在时,依然可以观察到这种效应,提示自LHC向视锥的负反馈和视锥谷氨酸转运体在此效应中不起显著作用.AMPA的不同调制作用提示,LHC上可能存在不同特性的AMPA受体亚型介导红敏和绿敏视锥的信号传递.     

2型糖尿病视网膜病变与胰岛素抵抗及β细胞功能的关系

目的:探讨新疆汉族2型糖尿病视网膜病变(DR)与胰岛素抵抗(IR)及β细胞功能的关系.方法:免散瞳眼底照相行眼底筛查我院内分泌科住院病人及体检正常人群258例,正常人(NC)83例、糖尿痛无视网膜病变(NDR)60例、糖尿病视网膜病变(DR)115例.测定其空腹血糖(FBG)、空腹胰岛素(FINS),计算胰岛素抵抗指数(HOMA-IR指数)、β细胞功能指数(HOMA-β指数),并测定其临床一般资料,记录身高、体重等.结果:NDR组、DR组HOMA-IR指数、HOMA-β指数明显高于NC组,差异有统计学意义(p<0.05),但NDR组与DR组相比,HOMA-IR指数、HOMA-β指数差异无统计学意义(p>0.05).2型糖尿病视网膜病变与FBG、FINS、HOMA.IR、HOMA-β呈正相关(p<0.01).多元Logistie回归分析显示病程、吸烟史、TG、Tc、尿微量白蛋白(UAE)、糖化血红蛋白(HbAlc)、血尿酸(SUA)、收缩压(SBP)HOMA-IR、HOMA-β为DR的危险因素.校正这些因素后DR仍与UAE、SUA、SBP、HOMA-IR、HOMA-β相关.结论:DR的发生与发展除了与病程、脂代谢紊乱、吸烟有关外,还与IR、β细胞功能、UAE及SUA等有关.     

Differences in kinetics between GABAC and GABAA receptors on carp retinal bipolar cells

The present work was undertaken to characterize kinetics, including activation, desensitization and deactivation, of responses mediated by GABAA and GABAC receptors on carp retinal bipolar cells, using the whole-cell patch-clamp technique. It was revealed that the GABAC response was generally slower in kinetics than the GABAA response. Activation kinetics of both the receptors could be well fit by monoexponential functions with time constants τ, being 44.57 ms (GABAC) and 10.86 ms (GABAA) respectively. Desensitization of the GABAA response was characterized by a fast and a slow exponential component with time constants of τfast = 2.16 s and τslow = 19.78 s respectively, whereas desensitization of the GABAC response was fit by a monoexponential function of the time constant τ = 6.98 s. Deactivation at both the receptors was adequately described by biexponential functions with time constants being much higher for the GABAC response (τfast = 674.8 ms; τslow = 2 090 ms) than those for the GABAA response (τfast = 42.07 ms; τslow = 275.1 ms). These differences in kinetics suggest that GABAC and GABAA receptors may be involved in processing signals in different frequency domains.     

Differences in kinetics between GABAC and GABAA receptors on carp retinal bipolar cells

The present work was undertaken to characterize kinetics, including activation, desensitization and deactivation, of responses mediated by GABAA and GABAc receptors on carp retinal bipolar cells, using the whole-cell patch-clamp technique. It was revealed that the GABAC response was generally slower in kinetics than the GABAA response. Activation kinetics of both the receptors could be well fit by monoexponential functions with time constants r, being 44.57 ms (GABAC) and 10.86 ms (GABAA) respectively. Desensitization of the GABAA response was characterized by a fast and a slow exponential component with time constants of τfast = 2.16 s and τslow = 19.78 s respectively, whereas desensitization of the GABAc response was fit by a monoexponential function of the time constant T = 6.98 s. Deactivation at both the receptors was adequately described by biexponential functions with time constants being much higher for the GABAC response (τfast = 674.8 ms; τslow = 2 090 ms) than those for the GABAA response     

Synaptic connections of cone bipolar cells that express the neurokinin 1 receptor in the rabbit retina

We have investigated and further characterized, in the rabbit retina, the synaptic connectivity of the ON-type cone bipolar cells that are immunoreactive for an antibody against the neurokinin-1 receptor (NK1R). NK1R-immunoreactive bipolar cell axons terminate in stratum 4 of the inner plexiform layer. The axons of NK1R-positive bipolar cells receive synaptic inputs from amacrine cells through conventional synapses and from putative AII amacrine cells via gap junctions. The major outputs from NK1R-positive bipolar cells make contacts with amacrine cell processes. The most frequent postsynaptic dyads comprise two amacrine cell processes. Double-labeling experiments with antibodies against NK1R and either calretinin or glycine have demonstrated that NK1R-immunoreactive bipolar cells form gap junctions with AII amacrine cells. Thus, NK1R-positive cone bipolar cells, together with calbindin-positive cone bipolar cells, may play an important role in transferring rod signals to the ON-type ganglion cells of the cone pathway in the rabbit retina.I.-B. Kim and M.R. Park contributed equally to this work.This work was supported by the Ministry of Science and Technology of Korea (grant no. M1-0108-00-0059; Neurobiology Support Grant).     

Differential effects of nitric oxide on rod and cone pathways in carp retina

The effects of nitric oxide (NO) on electroretinograms and light responses of horizontal cells intracellularly recorded from isolated, superfused carp retinas were studied. Sodium nitroprusside (SNP), an NO donor, suppressed scotopic b wave, while enhancing photopic b wave, and the effects could be blocked by hemoglobin, an NO chelator. Furthermore, following SNP application, light responses of rod horizontal cells were reduced in size and those of cone horizontal cells were increased. These results suggest that NO suppresses the activity of rod pathway, but enhances that of cone pathway in the outer retina. Moreover, the effects of methylene blue, an inhibitor of soluble guanylate cyclase, on rod and cone horizontal cells were just opposite to those of SNP, implying that the effects of NO may be mediated by cGMP. Project supported by the “Climbing Project” of the State Commission of Science and Technology (China) and the National Natural Science Foundation of China.     

Hypoosmotic and glutamate‐induced swelling of bipolar cells in the rat retina: comparison with swelling of Müller glial cells

Regulation of cellular volume is of great importance to avoid changes in neuronal excitability resulting from a decrease in the extracellular space volume. We compared the volume regulation of retinal glial (Müller) and neuronal (bipolar) cells under hypoosmotic and glutamate‐stimulated conditions. Freshly isolated slices of the rat retina were superfused with a hypoosmotic solution (60% osmolarity; 4 min) or with a glutamate (1 mM)‐containing isoosmotic solution (15 min), and the size changes of Müller and bipolar cell somata were recorded. Bipolar cell somata, but not Müller cell somata, swelled under hypoosmotic conditions and in the presence of glutamate. The hypoosmotic swelling of bipolar cell somata might be mediated by sodium flux into the cells, because it was not observed under extracellular sodium‐free conditions, and was induced by activation of metabotropic glutamate receptors and sodium‐dependent glutamate transporters. The glutamate‐induced swelling of bipolar cell somata was mediated by sodium chloride flux into the cells induced by activation of NMDA‐ and non‐NMDA glutamate receptors, glutamate transporters, and voltage‐gated sodium channels. The glutamate‐induced swelling of bipolar cell somata was abrogated by adenosine and γ‐aminobutyric acid, but not by vascular endothelial growth factor and ATP. The data may suggest that Müller cells, in contrast to bipolar cells, possess endogenous mechanisms which tightly regulate the cellular volume in response to hypoosmolarity and prolonged glutamate exposure. Inhibitory retinal transmission may regulate the volume of bipolar cells, likely by inhibition of the excitatory action of glutamate.     

Differences in kinetics between GABAC and GABAA receptors on carp retinal bipolar cells

The present work was undertaken to characterize kinetics, including activation, desensitization and deactivation, of responses mediated by GABA_A and GABA_C receptors on carp retinal bipolar cells, using the whole-cell patch-clamp technique. It was revealed that the GABA_C response was generally slower in kinetics than the GABA_A response. Activation kinetics of both the receptors could be well fit by monoexponential functions with time constants t, being 44.57 ms (GABA_C) and 10.86 ms (GABA_A) respectively. Desensitization of the GABA_Aresponse was characterized by a fast and a slow exponential component with time constants of τ_fast = 2.16 s and τ_slow = 19.78 s respectively, whereas desensitization of the GABA_C response was fit by a monoexponential function of the time constant τ = 6.98 s. Deactivation at both the receptors was adequately described by biexponential functions with time constants being much higher for the GABA_C response (τ_fast= 674.8 ms; τ_slow = 2 090 ms) than those for the GABA_A response (τ_fast = 42.07 ms; τ_slow = 275.1 ms). These differences in kinetics suggest that GABA_C and GABA_A receptors may be involved in processing signals in different frequency domains.     

TRPM1: The endpoint of the mGluR6 signal transduction cascade in retinal ON‐bipolar cells

For almost 30 years the ion channel that initiates the ON visual pathway in vertebrate vision has remained elusive. Recent findings now indicate that the pathway, which begins with unbinding of glutamate from the metabotropic glutamate receptor 6 (mGluR6), ends with the opening of the transient receptor potential (TRP)M1 cation channel. As a component of the mGluR6 signal transduction pathway, mutations in TRPM1 would be expected to cause congenital stationary night blindness (CSNB), and several such mutations have already been identified in CSNB families. Furthermore, expression of TRPM1 in both the retina and skin raises the possibility that a genetic link exists between certain types of visual and skin disorders.     

Glycine protection of PC-12 cells against injury by ATP-depletion

A distinctive mechanism of cell injury during ATP depletion involves the loss of cellular glycine. The current study examined whether provision of glycine during ATP depletion can prevent injury in PC-12 cells, a cell line with neuronal property. In addition, we have examined the role played by glycine receptors in cytoprotective effects of the amino acid. It was shown that ATP depletion led to plasma membrane damage in PC-12 cells, which was ameliorated by 0.25–5mM glycine. Cytoprotective activity of glycine was shared by alanine, but not by glutamate or -aminobutyric acid (GABA). Of interest, strychnine, an antagonist of glycine receptor, was also protective. The results, while suggesting the involvement of glycine receptor in cytoprotection, indicate that chloride channel activity of the receptor is dispensable. Such a scenario is further supported by the observation that removal of extracellular chloride did not affect ATP depletion–induced cell injury or its prevention by glycine. In short, this study has provided the first evidence for glycine protection of cells with neuronal properties. Cytoprotection may involve the glycine receptor; however, it can be dissociated from its channel activity.     

Amacrine cells differentially balance zebrafish color circuits in the central and peripheral retina

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Two-photon imaging reveals somatodendritic chloride gradient in retinal ON-type bipolar cells expressing the biosensor Clomeleon

A somatodendritic gradient of Cl(-) concentration ([Cl(-)](i)) has been postulated to generate GABA-evoked responses of different polarity in retinal bipolar cells, hyperpolarizing in OFF cells with low dendritic [Cl(-)](i), and depolarizing in ON cells with high dendritic [Cl(-)](i). As glutamate released by the photoreceptors depolarizes OFF cells and hyperpolarizes ON cells, the bipolars' antagonistic receptive field (RF) could be computed by simply integrating glutamatergic inputs from the RF center and GABAergic inputs from horizontal cells in the RF surround. Using ratiometric two-photon imaging of Clomeleon, a Cl(-) indicator transgenically expressed in ON bipolar cells, we found that dendritic [Cl(-)](i) exceeds somatic [Cl(-)](i) by up to 20 mM and that GABA application can lead to Cl(-) efflux (depolarization) in these dendrites. Blockers of Cl(-) transporters reduced the somatodendritic [Cl(-)](i) gradient. Hence, our results support the idea that ON bipolar cells employ a somatodendritic [Cl(-)](i) gradient to invert GABAergic horizontal cell input.