Structure And Function In Retinal Neurons

脊椎动物视网膜接收、处理和转换视觉信息。该研究项目阐明了视网膜神经元受体表达，视网膜神经回路和视网膜信息处理任务之间的关系。该研究目前使用急性分离的斑马鱼视网膜神经元和斑马鱼视网膜切片作为组织来源来检查斑马鱼模型。急性分离的视网膜双极细胞、水平细胞和光感受器细胞在培养中很容易被形态学鉴定。无长突细胞和神经节细胞可以通过标记技术鉴定。在视网膜切片中，细胞结构由从记录电极扩散的染料描绘。对神经递质的生理反应可以用电压敏感探针在分离的细胞中测定，也可以用全细胞膜片记录在视网膜切片中测定。在执行信息处理任务时，视网膜神经元表达独特的神经递质反应。双极细胞可以被从光感受器释放的谷氨酸兴奋或抑制，形成ON和OFF通路。GABA产生的抑制反应通常是非脱敏的、荷包牡丹碱不敏感的GABA-C型。视网膜神经处理的进一步描述可以在http://webvision.med.utah.edu/找到。采用全细胞膜片钳记录和抽吸吸管技术研究了斑马鱼视网膜切片双极细胞树突上谷氨酸受体的作用机制。记录的神经元用荧光黄染色，以将谷氨酸反应与BC形态相关联。BC轴突终末（AT）由轴突上的血管或血管曲张沿着排列，在轴突末端也有。AT分层模式确定了内丛状层（IPL）中的三个区域：厚的亚层a，具有三条AT带，IPL中部的狭窄无终末区，以及薄的亚层B，具有两条AT带。发生BC时，AT仅限于a层下（a组）、B层下（B组）或两个层下均存在AT（a/B组）。OFF-BC属于a组或a/B组。这些细胞对谷氨酸或红藻氨酸的反应是CNQX敏感的电导增加。恢复电位（Erev）范围为-0.6至+18 mV。用红藻氨酸盐和谷氨酸盐依次刺激双极细胞，发现除了对两种激动剂敏感的细胞外，还存在谷氨酸盐不敏感、红藻氨酸盐敏感的细胞群。ON-BC通过以下三种机制之一对谷氨酸做出反应：（a）电导随Erev ~ 0 mV降低，由L-（+）-2-氨基-4-膦酰基丁酸（APB）或反式-1-氨基-1，3-环戊烷二羧酸模拟（trans-ACPD），（B）谷氨酸门控氯离子电导增加（IGlu样）特征为Erev接近ECl（其中EC 1是氯平衡电位）和通过细胞外Li+/Na+取代的部分阻断，或（c）同时激活APB和氯离子机制，以在所有保持电位下产生外向电流响应。APB样反应仅在B组的BC中发现，在亚板层B深处有单个AT分支;而表达IGlu样电流的细胞有一个或多个AT，并且发生在组B或a/B中。复层细胞（a/B组）很常见，发生在ON-或OFF-BC生理状态下。OFF-BC通常在亚板a中具有一个或多个AT，而在亚板B中仅具有一个AT。相反，复层ON-BC在亚板层B有一个或多个AT，在亚板层a深处有一个AT分支.多层ON-BC仅表达IGlu样机制。斑马鱼视网膜中的视觉处理涉及至少13种BC类型。其中一些BC在ON和OFF亚板层中都有AT，这表明ON和OFF输入在整个IPL中起着重要作用。

The vertebrate retina receives, processes and transforms visual information. The research program elucidates the relationships between receptor expression on retinal neurons, the neural circuitry of the retina, and retinal information processing tasks. The study currently examines the zebrafish model using, as tissue source, acutely dissociated zebrafish retinal neurons and zebrafish retinal slices. Acutely dissociated retinal bipolar and horizontal and photoreceptor cells are readily identified morphologically in culture. Amacrine and ganglion cells can be identified through labeling techniques. In retinal slices cell structure is delineated by dye diffusing from the recording electrode. Physiological responses to neurotransmitters can be assayed with voltage-sensitive probes in isolated cells, and by whole-cell patch recording in retinal slice. In performing information processing tasks, retinal neurons express unique neurotransmitter responses. Bipolar cells may be either excited or inhibited by glutamate released from photoreceptors forming ON and OFF pathways. GABA-generated inhibitory responses are commonly of the non-desensitizing, bicuculline-insensitive GABA-C type. Further descriptions of retinal neural processing may be found at http://webvision.med.utah.edu/. Whole-cell patch recording and puff pipette techniques were used to identify glutamate receptor mechanisms on bipolar cell (BC) dendrites in the zebrafish retinal slice. Recorded neurons were stained with Lucifer Yellow, to correlate glutamate responses with BC morphology. BC axon terminals (ATs) consisted of swellings or varicosities along the axon, as well as at its end. AT stratification patterns identified three regions in the inner plexiform layer (IPL): a thick sublamina a, with three bands of ATs, a narrow terminal-free zone in the mid-IPL, and a thin sublamina b, with two bands of ATs. BCs occurred with ATs restricted to sublamina a (Group a), sublamina b (Group b) or with ATs in both sublaminae (Group a/b). OFF-BCs belonged to Group a or Group a/b. These cells responded to glutamate or kainate with a CNQX-sensitive conductance increase. Reversal potential (Erev) ranged from -0.6 to +18 mV. Bipolar cells stimulated sequentially with both kainate and glutamate revealed a population of glutamate-insensitive, kainate-sensitive cells in addition to cells sensitive to both agonists. ON-BCs responded to glutamate via one of three mechanisms: (a) a conductance decrease with Erev ~ 0 mV, mimicked by L-(+)-2-amino- 4-phosphonobutyric acid (APB) or trans-1-amino-1,3- cyclopentanedicarboxylic acid (trans-ACPD), (b) a glutamate- gated chloride conductance increase (IGlu-like) characterized by Erev near ECl (where ECl is the chloride equilibrium potential) and by partial blockade by extracellular Li+/Na+ substitution or (c) the activation of both APB and chloride mechanisms simultaneously to produce a response with outward currents at all holding potentials. APB-like responses were found only among BCs in Group b, with a single AT ramifying deep within sublamina b; whereas, cells expressing IGlu-like currents had one or more ATs, and occurred within Groups b or a/b. Multistratified cells (Group a/b) were common and occurred with either ON- or OFF-BC physiology. OFF-BCs typically had one or more ATs in sublamina a and only one AT in sublamina b. In contrast, multistratified ON- BCs had one or more ATs in sublamina b and a single AT ramifying deep in sublamina a. Multistratified ON-BCs expressed the IGlu- like mechanism only. Visual processing in the zebrafish retina involves at least 13 BC types. Some of these BCs have ATs in both the ON- and OFF-sublaminae, suggesting a significant role for ON- and OFF-inputs throughout the IPL.