Function of Basal Synapses at Mammalian Photoreceptors

描述（由申请人提供）：本研究探讨了哺乳动物视锥光感受器突触的特化结构与突触后双极细胞通路中对视觉感知至关重要的信号传导之间的关系。视锥光感受器在明亮的照明条件下介导视觉，并使用谷氨酸作为它们的递质。视锥细胞接触两种功能类别的双极细胞，开和关，它们具有不同的谷氨酸受体，使它们去兴奋（即，信号）。双极细胞的每个功能类别进一步细分为4-5个解剖学亚型（例如，b2、b3、b7）。最近的工作表明，Off双极细胞的不同解剖亚型表达不同类型的谷氨酸受体（AMPA或红藻氨酸），与视锥末端接触的数量不同，并且在距离递质释放位点不同的距离处接触视锥末端。递质扩散距离、接触数量和受体类型的差异表明，Off双极细胞的每个亚型可以处理锥信号的不同分量。该项目的主要目标是确定关闭双极细胞的不同亚型中信号的特性，并将这些特性与突触的结构和药理学联系起来。通过同时电压钳位来自地松鼠的视锥优势视网膜的切片中的突触前视锥和突触后双极细胞来研究视锥到关双极细胞突触的传输。第一组实验的目的是检验b2细胞突触专门传递锥体电压高频波动的假设，并研究其潜在机制。具体的实验将a）确定在熄灯时瞬时去极化的幅度如何随光脉冲持续时间变化，和B）使用时间闪烁来确定由视锥细胞到Off双极细胞突触最佳传输的频率。第二组实验的目的是检验稳定突触传递的增益在视锥细胞到b3和b7细胞突触上是不同的这一假设。具体的实验将确定锥接触数和受体脱敏如何影响稳定的突触增益。第三组实验的目的是检验锥谷氨酸转运蛋白在控制裂隙谷氨酸浓度中仅起很小作用的假设。具体的实验将确定在何种程度上，地面松鼠锥重新捕获释放谷氨酸，并确定谷氨酸转运蛋白相对于带状释放网站的位置。公共卫生相关性：这个项目的目标是了解哺乳动物锥体突触的精细结构如何决定其在视觉中的功能。最终，涉及视锥细胞变性的疾病将通过植入外源性视锥细胞或从内源性干细胞生长新的视锥细胞来治疗。这种方法成功的程度可能取决于视锥细胞与视网膜中其他细胞进行结构正确的突触接触的能力。

DESCRIPTION (provided by applicant): This study addresses the relationship between the specialized structure of the mammalian cone photoreceptor synapse and signaling in postsynaptic bipolar cell pathways that are critical for visual perception. Cone photoreceptors mediate vision under conditions of bright illumination and use glutamate as their transmitter. A cone contacts two functional classes of bipolar cells, On and Off, which have different glutamate receptors that cause them to depolarize (i.e., signal) either at light-on or light-off, respectively. Each functional class of bipolar cell is further subdivided into 4-5 anatomical subtypes (e.g., b2, b3, b7). Recent work has shown that the different anatomical subtypes of Off bipolar cells express different types of glutamate receptors (AMPA or kainate), make different numbers of contacts with a cone terminal, and contact the cone terminal at distinct distances from transmitter release sites. The differences in transmitter diffusion distance, contact number, and receptor type suggest that each subtype of Off bipolar cell could process a different component of the cone signal. The main goal of this project is to determine the properties of the signals in the different subtypes of Off bipolar cells, and to relate those properties to the structure and pharmacology of the synapse. Transmission at the cone to Off bipolar cell synapse will be studied by simultaneously voltage clamping a presynaptic cone and a postsynaptic bipolar cell in slices from the cone dominant retina of the ground squirrel. The aim of the first set of experiments is to test the hypothesis that the b2 cell synapse is specialized to transmit high frequency fluctuations in cone voltage, and examine the underlying mechanisms. Specific experiments will a) determine how the amplitude of the transient depolarization at light-off varies with light pulse duration and b) use temporal flicker to determine the frequencies best transmitted by cone to Off bipolar cell synapses. The aim of the second set of experiments is to test the hypothesis that the gain of steady synaptic transmission is different at cone to b3 and b7 cell synapses. Specific experiments will determine how cone contact number and receptor desensitization affect steady synaptic gain. The aim of the third set of experiments is to test the hypothesis that cone glutamate transporters play only a small role in controlling the cleft glutamate concentration. Specific experiments will determine the extent to which ground squirrel cones recapture released glutamate and determine the locations of glutamate transporters relative to ribbon release sites. PUBLIC HEALTH RELEVANCE: The goal of this project is to understand how the elaborate structure of the mammalian cone synapse determines its function in vision. Ultimately, diseases involving cone photoreceptor degeneration will be treated by either implanting exogenous cones or growing new cones from endogenous stem cells. The degree to which such approaches succeed may be governed by the ability of the cones to make structurally correct synaptic contacts with other cells in the retina.