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：
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
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.

视网膜检测和传输大量的视觉信息。色带突触是脊椎动物视网膜电路的关键组成部分，在通往大脑的信号传导途径中形成了第一和第二突触的元素。丝带的专业形态和功能大概赋予了它们独特的大量和快速神经递质释放的能力，这对于有效的视觉信息处理和编码是必不可少的。然而，在截然不同的环境光条件下以及白天/夜间周期中，调节和维持发射机突触的发射器输出的基本细胞机制知之甚少。由于它们的尺寸较大，我们能够补丁夹单金鱼双极细胞端子。这使我们能够测量突触前的CA电流和诱发膜电容的变化，即实时测定突触囊泡外胞毒性和内吞作用。我们发现，突触末端的夜间释放效率大大降低，因此大量的CA电流引起了少量的胞吐作用。相反，相对较小的Ca电流会在白天引起大量的胞吐作用。此外，我们发现众所周知的中间代谢产物NAD+和NADH调节了色带突触输出，也许是通过与新型和主要的带状构成蛋白ribeye的相互作用。因此，第一个要检验的假设是，在昼夜节律循环中，胞吞作用的效率变化（与突触的色带形态和代谢状态的变化相似），以及该色带功能由反映细胞能级的代谢产物调节。我们还发现，升高的内部CL-ION水平抑制了色带突触时内吞作用的速率。因此，要检验的第二个假设是，通过强末端的强力输入通过末端的强力输入直接调节囊泡回收率通过抑制内吞作用，这是回收过程中的第一步。这一发现表明，作为调节囊泡循环的第二个使者的新作用。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内突触囊泡的迁移率。关于色带突触如何调节囊泡的迁移率和聚类，知之甚少。要测试的第三个假设是，磷酸化调节了色带突触时的囊泡回收和迁移率。因此，这些研究将增加我们对色带突触的理解，作为适应各种条件的动态结构，从而有效地传递了各种刺激。