Dynamic Modulation of Retinal Ribbon-Type Synapses

视网膜带状突触的动态调制

• 批准号: 7057232
• 负责人: HENRIQUE Prado VON GERSDORFF
• 金额: $ 22.12万
• 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/7057232
• 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，在通往大脑的信号通路中形成第一和第二突触前元件。带状的特殊形态和功能可能赋予了它们丰富和快速释放神经递质的独特能力，这被认为是有效处理和编码视觉信息所必需的。然而，在不同的环境光条件下以及在白天和夜间循环中，调节和维持带状突触的递质输出的潜在细胞机制尚不清楚。由于它们的大尺寸，我们能够膜片钳单金鱼双极细胞终端。这使我们能够测量突触前Ca电流和诱发膜电容的变化，从而实时测定突触囊泡的胞吐和内吞作用。我们发现突触末端在夜间的释放效率大大降低，因此大的Ca电流引起少量的胞吐。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物NAD+和NADH可能通过与一种新的主要条带组成蛋白RIBEYE的相互作用来调节条带突触的输出。因此，第一个需要验证的假设是，细胞外吐的效率在一个昼夜周期中在带状突触发生变化（这与带状形态和突触代谢状态的变化相似），而带状功能是由反映细胞能量水平的代谢物调节的。我们还发现，内部cl -离子水平升高会抑制带状突触的内吞速率。因此，第二个需要验证的假设是，通过末端强gaba能输入的cl内流通过抑制内吞作用（循环过程的第一步）直接调节囊泡循环的速度。这一发现提示了Cl离子作为调节囊泡循环的第二信使的新作用。最后，我们有初步证据表明，去磷酸化极大地抑制了双极细胞末端突触囊泡的移动性。关于带状突触如何调节囊泡的移动和聚集，我们所知甚少。第三个有待验证的假设是，磷酸化调节了带状突触的囊泡循环和流动性。这些研究将增加我们对带状突触作为一种动态结构的理解，这种结构可以适应不同的条件，从而有效地传递各种刺激。