Transmitter substances of retinal neurons

关于突触传递的知识对于理解神经系统是必不可少的。本研究的目的是了解突触递质在脊椎动物视网膜中的作用。我们利用膜片钳技术在全细胞形态下记录了孤立神经元的膜电流。从金鱼、乌龟和老鼠的视网膜中分离出细胞。下面是一些主要的发现。光感受器摄取l -谷氨酸。现在普遍认为l -谷氨酸是由光感受器释放的。l -谷氨酸通过运输系统被光感受器吸收。Na^+的电化学梯度是输运的能量来源；3个Na^+与每个谷氨酸模共运输。因此，这个系统是电致的，导致所有亚型的光感受器去极化。这一机制可能参与了异源光感受器之间的兴奋性相互作用-氨基丁酸（GABA）对双极细胞的抑制作用。GABA受体介导的氯离子通道打开诱导金鱼双极细胞超极化小鼠双极细胞瞬态钙电流。小鼠双极细胞钙电流（I_<ca>）为t型，表现为快速失活。I_< _bb_0流经轴突末端和体细胞。假设双极电池端发射机释放也是瞬态的。因此，小鼠双极细胞的I_<ca>可能参与了形成腺细胞和神经节细胞的瞬态光诱发反应。海龟视网膜中感光细胞和水平细胞之间的连接。龟锥的亚型很容易通过它们的彩色油滴在形态学上识别出来。利用该指数，我们分析了光感受器与水平细胞的连通性。与一般的看法相反，发现红色敏感锥与H_2和H_3水平细胞有直接的联系。在此基础上讨论了色觉模型。少

Knowledge on the synapic transmission is essential for the understanding of a nervous system. The aim of the present study was to understand the action of synaptic transmitter in the vertebrate retina. We recorded membrane currents of solitary neurons by using patch clamp technique in the whole cell configuration. Cells were dissociated from the retina of goldfish, turtle and mouse. The following is a list of major findings.1. Uptake of L-glutamate by photoreceptors. It is now generally accepted that L-glutamate is released from photoreceptors. L-Glutamate is taken up by photoreceptors by a transport system. Electrochemical gradient of Na^+ is the enegy source for transport; 3 Na^+ are co-transported with each glutamate modecule. Thus, this system is electrogenic, causing depolarization in all subtypes of photoreceptors. It is likely that this mechanism contribute in excitatory interaction among heterologous photoreceptors.2 Inhibition mediated by -aminobutyric acid (GABA) from amacrin … More e cell to bipolar cell. GABA induced hyper-polarization in goldfish bipolar cells by opening chloride channels mediated by GABAalpha receptor.3. Transient calcium current of mouse bipolar cells. Calcium current (I_<ca>) in mouse bipolar cells is T-type showing rapid inactivation. I_<ca> flowed through the axon terminal as well as the soma. It is hypothesized that the transmitter release from bipolar cell terminal is also transient. Thus, I_<ca> of mouse bipolar cells may contribute in shaping transient light evoked responses in amacrine and ganglion cells.4. Connectivity between photoreceptors and horizontal cells in the turtle retina. Subtypes of turtle cones are readily identified morphologically by their colored oil droplets. Using this index, we analyzed connectivity of photoreceptors and horizontal cells. Contrary to the general belief, red-sensitive cones were found to make direct connection to H_2 and H_3 horizontal cells. Color vision models are discussed based on this new finding. Less