Dynamic Modulation of Retinal Ribbon-Type Synapses

视网膜带状突触的动态调制

• 批准号: 6751897
• 负责人: HENRIQUE Prado VON GERSDORFF
• 金额: $ 22.65万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-05-01 至 2007-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6751897
• 关键词: GABA receptor; calcium ion; chloride ion; circadian rhythms; confocal scanning microscopy; dissection; electron microscopy; endocytosis; exocytosis; fluorescence microscopy; goldfish; immunocytochemistry; morphology; neurotransmitters; nicotinamide adenine dinucleotide; phosphorylation; retina; retinal bipolar neuron; synaptic vesicles; tissue /cell preparation; visual stimulus; voltage /patch clamp

The retina detects and transmits large amounts of visual information quickly and reliably. Ribbon synapses are key components of the vertebrate retinal circuitry, forming the first and second presynaptic elements in the signaling pathway to the brain. The specialized morphology and function of the ribbons presumably endows them with a unique capacity for copious and fast neurotransmitter release, which is thought to be essential for the efficient processing and encoding of visual information. Nevertheless, the underlying cellular mechanisms that modulate and maintain transmitter output from ribbon synapses under vastly different ambient light conditions and during the daytime/nighttime cycle are poorly understood. Due to their large size, we are able to patch-clamp single goldfish bipolar cell terminals. This allows us to measure both presynaptic Ca currents and evoked changes in membrane capacitance that assay synaptic vesicle exocytosis and endocytosis in real time. We have found that synaptic terminals have a greatly reduced efficiency of release at night, so that large Ca currents evoke small amounts of exocytosis. Conversely, relatively smaller Ca currents evoke much larger amounts of exocytosis during daytime. In addition, we have found that the well-known intermediate metabolites NAD+ and NADH modulate ribbon synapse output, perhaps via their interaction with a novel and major ribbon constituent protein RIBEYE. Thus, the first hypothesis to be tested is that the efficiency of exocytosis changes at a ribbon synapse in a circadian cycle (that parallels changes in ribbon morphology and metabolic state of the synapse), and that ribbon function is modulated by metabolites that reflect cellular energy levels. We have also found that elevated levels of internal Cl-ions inhibit the rate of endocytosis at ribbon synapses. Therefore, the second hypothesis to be tested is that Cl-influx via the strong GABAergic input at the terminal directly modulates the rate of vesicle recycling by inhibiting endocytosis, the first step in the recycling process. This finding suggests a novel role for Cl- ions as second messengers that modulate vesicle cycling. Finally, we have preliminary evidence that dephosphorylation drastically inhibits the mobility of synaptic vesicles within bipolar cell terminals. Very little is known about how ribbon synapses regulate vesicle mobility and clustering. The third hypothesis to be tested is that phosphorylation regulates vesicle recycling and mobility at ribbon synapses. These studies will thus increase our understanding of ribbon synapses as dynamic structures that adapt to diverse conditions so as to efficiently transmit a wide array of stimuli.

视网膜能够快速可靠地检测和传输大量的视觉信息。带状突触是脊椎动物视网膜回路的关键组成部分，形成通往大脑的信号通路中的第一和第二突触前元件。带状物的特殊形态和功能可能赋予它们丰富而快速的神经递质释放的独特能力，这被认为是有效处理和编码视觉信息所必需的。然而，在截然不同的环境光条件下和在白天/夜间周期期间，调节和维持带状突触的发射器输出的潜在细胞机制知之甚少。由于它们的大尺寸，我们能够膜片钳单个金鱼双极细胞终端。这使我们能够测量突触前钙电流和诱发的膜电容的变化，测定突触囊泡胞吐和内吞作用在真实的时间。我们发现突触末梢在夜间释放的效率大大降低，因此大的钙电流引起少量的胞吐作用。相反，相对较小的钙电流在白天引起大量的胞吐。此外，我们还发现，众所周知的中间代谢产物NAD+和NADH调节带状突触输出，可能是通过它们与一种新的和主要的带状组成蛋白RIBEYE的相互作用。因此，要测试的第一个假设是，在昼夜节律周期中，胞吐作用的效率在带状突触处发生变化（这与带状突触形态和突触代谢状态的变化平行），并且带状功能受到反映细胞能量水平的代谢物的调节。我们还发现，内部Cl-离子水平升高抑制带状突触的内吞率。因此，要测试的第二个假设是，Cl-内流通过在末端的强GABA能输入直接调节囊泡再循环的速率，通过抑制胞吞作用，再循环过程中的第一步。这一发现表明了一个新的作用，Cl-离子作为第二信使，调节囊泡循环。最后，我们有初步的证据表明，去磷酸化大大抑制双极细胞终端内的突触囊泡的流动性。很少有人知道带状突触如何调节囊泡的流动性和集群。第三个有待检验的假设是磷酸化调节带状突触的囊泡循环和流动性。因此，这些研究将增加我们对带状突触的理解，带状突触是适应不同条件的动态结构，可以有效地传递各种刺激。