PDF(Pubmed)
Abstract：
The ability of the visual system to relay meaningful information over a wide range of lighting conditions is critical to functional vision, and relies on mechanisms of adaptation within the retina that adjust sensitivity and gain as ambient light changes. Photoreceptor synapses represent the first stage of image processing in the visual system, thus activity-driven changes at this site are a potentially powerful, yet under-studied means of adaptation. To gain insight into these mechanisms, the abundance and distribution of key synaptic proteins involved in photoreceptor to ON-bipolar cell transmission were compared between light-adapted mice and mice subjected to prolonged dark exposure (72 hours), by immunofluorescence confocal microscopy and immunoblotting. We also tested the effects on protein abundance and distribution of 0.5-4 hours of light exposure following prolonged darkness. Proteins examined included the synaptic ribbon protein, ribeye, and components of the ON-bipolar cell signal transduction pathway (mGluR6, TRPM1, RGS11, GPR179, Goα). The results indicate a reduction in immunoreactivity for ribeye, TRPM1, mGluR6, and RGS11 following prolonged dark exposure compared to the light-adapted state, but a rapid restoration of the light-adapted pattern upon light exposure. Electron microscopy revealed similar ultrastructure of light-adapted and dark-adapted photoreceptor terminals, with the exception of electron dense vesicles in dark-adapted but not light-adapted ON-bipolar cell dendrites. To assess synaptic transmission from photoreceptors to ON-bipolar cells, we recorded electroretinograms after different dark exposure times (2, 16, 24, 48, 72 hours) and measured the b-wave to a-wave ratios. Consistent with the reduction in synaptic proteins, the b/a ratios were smaller following prolonged dark exposure (48-72 hours) compared to 16 hours dark exposure (13-21%, depending on flash intensity). Overall, the results provide evidence of light/dark-dependent plasticity in photoreceptor synapses at the biochemical, morphological, and physiological levels.
摘要：
视觉系统在广泛的照明条件下传递有意义的信息的能力对于功能性视觉至关重要，并依赖于视网膜内的适应机制，随着环境光的变化调整灵敏度和增益。光感受器突触代表视觉系统中图像处理的第一阶段，因此，活动驱动的变化在这个网站是一个潜在的强大，然而，对适应手段的研究不足。为了深入了解这些机制，在光适应小鼠和长期黑暗暴露（72小时）的小鼠之间，比较了参与光感受器到ON双极细胞传递的关键突触蛋白的丰度和分布，通过免疫荧光共聚焦显微镜和免疫印迹。我们还测试了长时间黑暗后暴露0.5-4小时对蛋白质丰度和分布的影响。检查的蛋白质包括突触带蛋白，ribeye,和ON双极细胞信号传导途径的组成部分（mGluR6，TRPM1，RGS11，GPR179，Goα）。结果表明，ribeye的免疫反应性降低，TRPM1、mGluR6和RGS11与光适应状态相比，长时间暗曝光后，而是在曝光后快速恢复适应光的图案。电子显微镜显示光适应和暗适应的感光体终端的超微结构相似，暗适应但不适应光的双极细胞树突中的电子致密囊泡除外。为了评估从光感受器到双极型细胞的突触传递，我们记录了不同黑暗暴露时间(2,16,24,48,72小时)后的视网膜电图,并测量了b波与a波的比值.与突触蛋白的减少一致，与16小时黑暗暴露相比，长期黑暗暴露（48-72小时）后的b/a比率较小（13-21％，取决于闪光强度)。总的来说,结果提供了光亮/暗依赖性可塑性的证据光感受器突触在生化，形态学,和生理水平。
