Paul Flechsig Institute for Brain Research, Leipzig University, Leipzig, Germany.
Department of Physical Sciences, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico.
Exp Eye Res. 2018 Aug;173:91-108. doi: 10.1016/j.exer.2018.05.009. Epub 2018 May 25.
In this study, we show the capability of Müller glial cells to transport light through the inverted retina of reptiles, specifically the retina of the spectacled caimans. Thus, confirming that Müller cells of lower vertebrates also improve retinal light transmission. Confocal imaging of freshly isolated retinal wholemounts, that preserved the refractive index landscape of the tissue, indicated that the retina of the spectacled caiman is adapted for vision under dim light conditions. For light transmission experiments, we used a setup with two axially aligned objectives imaging the retina from both sides to project the light onto the inner (vitreal) surface and to detect the transmitted light behind the retina at the receptor layer. Simultaneously, a confocal microscope obtained images of the Müller cells embedded within the vital tissue. Projections of light onto several representative Müller cell trunks within the inner plexiform layer, i.e. (i) trunks with a straight orientation, (ii) trunks which are formed by the inner processes and (iii) trunks which get split into inner processes, were associated with increases in the intensity of the transmitted light. Projections of light onto the periphery of the Müller cell endfeet resulted in a lower intensity of transmitted light. In this way, retinal glial (Müller) cells support dim light vision by improving the signal-to-noise ratio which increases the sensitivity to light. The field of illuminated photoreceptors mainly include rods reflecting the rod dominance of the of tissue. A subpopulation of Müller cells with downstreaming cone cells led to a high-intensity illumination of the cones, while the surrounding rods were illuminated by light of lower intensity. Therefore, Müller cells that lie in front of cones may adapt the intensity of the transmitted light to the different sensitivities of cones and rods, presumably allowing a simultaneous vision with both receptor types under dim light conditions.
在这项研究中，我们展示了 Müller 胶质细胞在爬行动物的反转视网膜中传输光的能力，特别是在眼镜凯门鳄的视网膜中。因此，证实了较低等脊椎动物的 Müller 细胞也能提高视网膜的光传输效率。对新鲜分离的视网膜全层进行共焦成像，保留了组织的折射率景观，表明眼镜凯门鳄的视网膜适应于弱光条件下的视觉。对于光传输实验，我们使用了一种设置，其中两个轴向对准的物镜从两侧对视网膜进行成像，将光投射到内（玻璃体）表面，并在视网膜后面的受体层检测传输光。同时，共焦显微镜获得了嵌入在活体组织中的 Müller 细胞的图像。将光投射到内丛状层内的几个代表性 Müller 细胞干上，即（i）具有直线取向的干，（ii）由内突形成的干，和（iii）分裂成内突的干，与传输光强度的增加相关。将光投射到 Müller 细胞终足的外围导致传输光的强度降低。通过这种方式，视网膜神经胶质（Müller）细胞通过提高信号噪声比来支持弱光视觉，从而增加对光的灵敏度。受光的光感受器的区域主要包括反射组织的棒状优势的棒状光感受器。具有下游视锥细胞的 Müller 细胞亚群导致视锥细胞的高强度照明，而周围的棒状光感受器则被低强度的光照明。因此，位于视锥细胞前面的 Müller 细胞可能会根据视锥细胞和棒状光感受器的不同灵敏度来调节传输光的强度，大概允许在弱光条件下同时使用这两种受体类型进行视觉。
