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殊结构与对视觉感知至关重要的突触后双极细胞通路信号传导之间的关系。锥体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。一个锥体接触两种功能类型的双极细胞，开和关，这两种细胞有不同的谷氨酸受体，分别导致它们在开或关时去极化（即信号）。双相细胞的每个功能类别又进一步细分为4-5个解剖亚型（如b2、b3、b7）。最近的研究表明，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kainate），与锥体末端的接触次数不同，并且与锥体末端的接触距离与递质释放位点不同。发射器扩散距离、接触数和受体类型的差异表明，Off双极细胞的每个亚型可以处理不同的锥体信号成分。该项目的主要目标是确定Off双极细胞不同亚型信号的特性，并将这些特性与突触的结构和药理学联系起来。通过在地鼠视锥显性视网膜切片中同时夹紧突触前视锥细胞和突触后视双极细胞，研究锥体到关闭双极细胞突触的传输。第一组实验的目的是验证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)确定熄灯时瞬态去极化的振幅如何随光脉冲持续时间的变化，b)使用时间闪烁来确定锥体到关闭双极细胞突触的最佳传输频率。第二组实验的目的是验证一个假设，即稳定突触传递的增益在锥体到b3和b7细胞突触是不同的。具体的实验将确定锥体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验证锥体谷氨酸转运体在控制谷氨酸浓度中只起很小作用的假设。具体的实验将确定地鼠视锥在多大程度上重新捕获释放的谷氨酸，并确定谷氨酸转运蛋白相对于带状释放位点的位置。公共卫生相关性：该项目的目标是了解哺乳动物视锥突触的复杂结构如何决定其在视觉中的功能。最终，涉及锥体光感受器变性的疾病将通过植入外源锥体或从内源干细胞培养新的锥体来治疗。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.