Dynamic Modulation of Retinal Ribbon-Type Synapses

视网膜带状突触的动态调制

基本信息

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
项目类别：
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

项目摘要

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.

视网膜快速可靠地检测并传输大量视觉信息。带状突触是脊椎动物视网膜电路的关键组成部分，形成大脑信号传导通路中的第一和第二突触前元件。丝带的特殊形态和功能可能赋予它们大量和快速释放神经递质的独特能力，这被认为对于视觉信息的有效处理和编码至关重要。然而，在截然不同的环境光条件下和白天/夜间周期中调节和维持带状突触发射器输出的潜在细胞机制尚不清楚。由于其尺寸较大，我们能够对单个金鱼双极细胞端子进行膜片钳。这使我们能够测量突触前 Ca 电流和膜电容诱发的变化，从而实时测定突触小泡的胞吐作用和内吞作用。我们发现突触末梢在夜间的释放效率大大降低，因此大的 Ca 电流会引起少量的胞吐作用。相反，白天相对较小的 Ca 电流会引起更大量的胞吐作用。此外，我们还发现众所周知的中间代谢物 NAD+ 和 NADH 可能通过与一种新型的主要带状组成蛋白 RIBEYE 相互作用来调节带状突触输出。因此，要测试的第一个假设是，带状突触的胞吐作用效率在昼夜节律周期中发生变化（与带状突触形态和代谢状态的变化平行），并且带状功能受到反映细胞能量的代谢物的调节水平。我们还发现，内部氯离子水平升高会抑制带状突触的内吞作用速率。因此，要测试的第二个假设是，Cl-通过末端强 GABA 能输入流入，通过抑制内吞作用（回收过程的第一步）直接调节囊泡回收率。这一发现表明 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会极大地抑制双极细胞末梢内突触小泡的移动性。关于带状突触如何调节囊泡运动和聚集，人们知之甚少。要测试的第三个假设是磷酸化调节带状突触的囊泡回收和移动性。因此，这些研究将增进我们对带状突触作为动态结构的理解，它能够适应不同的条件，从而有效地传递各种刺激。