BIOPHYSICAL MECHANISMS OF SINGLE PHOTON DETECTION

描述(申请人提供)：暗适应视觉的能力 多年来，人们已经知道了计算吸收光子的系统；然而， 使光子检测和计数成为可能的生物物理机制是 我不明白。许多杆状视觉发生在光的水平上，光子 吸收很少发生；因此，两种转导途径中的任何一种都失败了 光子或将产生的信号严重传输到双极电池 会损害视杆视力。视觉敏感度对如何 吸收的光子被转换成电信号，以及这些 电信号通过杆-双极突触传递。当前 对信号转导和突触传递的理解无法解释 为了这种水平的表现。这里提出的实验将决定如何 关于光子吸收的数量和时间的准确信息是 在杆状信号中，什么噪声源限制了这种准确性和 是什么机制允许这些反应可靠地传输到双相 细胞。 光信号转导的研究将探讨其功能意义。 杆子对每个被吸收的物体产生几乎相同的反应的能力 光子。特别是，我们将测试这种重现性是 对杆状视觉的时间敏感性至关重要--也就是 准确地表示光子吸收的时间。这些研究还将 确定杆件信号中的其他噪声源的特征并确定其 对限制棒的检测和时间灵敏度的贡献 信号。这些是进一步了解 感光信号与噪声、视觉敏感度的关系。 对突触传递的研究将决定单光子反应的方式 可靠地传输到视网膜中的双极细胞。两期将收到 特别注意：(1)单光子响应与其他噪声的分离 棒中的源通过信号传输中的阈值非线性；以及(2) 棒传递信号过程中暗闪光响应动力学的变化 敬双极星。通过控制杆件直接研究信号的传递 电压，同时记录产生的双极响应。这些实验将 进一步了解非尖峰细胞的突触是如何工作的，以及 突触机制与视觉敏感性之间的关系。

DESCRIPTION (provided by applicant): The ability of the dark-adapted visual system to count absorbed photons has been known for many years; however, the biophysical mechanisms which make photon detection and counting possible are not understood. Much of rod vision occurs at light levels where photon absorptions occur rarely; thus, failure of either transduction of single photons or transmission of the resulting signals to bipolar cells severely impairs rod vision. Visual sensitivity places strict constraints on how absorbed photons are transduced into electrical signals and how these electrical signals are transmitted across the rod-bipolar synapse. Current understanding of signal transduction and synaptic transmission cannot account for this level of performance. Experiments proposed here will determine how accurately information about the number and timing of photon absorptions is represented in the rod signals, what source of noise limits this accuracy and what mechanisms permit reliable transmission of these responses to bipolar cells. Studies of phototransduction will investigate the functional significance of the rod's ability to produce a nearly identical response to each absorbed photon. In particular, we will test the idea that this reproducibility is critical for the temporal sensitivity of rod vision - that is the ability to represent the time of photon absorption accurately. These studies will also characterize the other noise sources in the rod signals and determine their contribution to limiting the detection and temporal sensitivity of the rod's signals. These are requisite measurements to further understanding of the relationship between photoreceptor signal and noise and visual sensitivity. Studies of synaptic transmission will determine how single photon responses are reliably transmitted to bipolar cells in the retina. Two issues will receive particular attention: (1) separation of single photon response from other noise sources in the rods by a thresholding nonlinearity in signal transfer; and (2) changes in the kinetics of the dim flash response in signal transfer from rods to bipolars. Signal transfer will be studied directly by controlling the rod voltage while recording the resulting bipolar response. These experiments will further the general understanding of how synapses in non-spiking cells work and the relation between synaptic mechanisms and visual sensitivity.