Braekevelt C R, Smith S A, Smith B J
Department of Zoology, The University of Western Australia, Nedlands, Australia.
Anat Rec. 1998 Nov;252(3):453-61. doi: 10.1002/(SICI)1097-0185(199811)252:3<453::AID-AR13>3.0.CO;2-3.
The structure and arrangement of both light- and dark-adapted retinal photoreceptors of Oreochromis niloticus L. were studied. Eyes of four light-adapted and four dark-adapted O. niloticus were fixed routinely for light and transmission electron microscopy. Rods, single cones, and double (twin) cones were present in a ratio of 30:1:2, respectively. Light-adapted rods were tall, extending into the retinal epithelial layer. Rod inner segments showed a distal ellipsoid of mitochondria that narrowed dramatically in the myoid region. Dark-adapted rod inner segments were much shorter with a thicker myoid region, indicating photomechanical movement. Rod synaptic spherules were small, with both superficial synapses and invaginated sites. Single cones were similar to individual members of a double cone. Cone outer segments consisted of uniform discs with a single incisure. All cones displayed a short, tapering outer segment, a large ellipsoid of mitochondria, and a myoid region rich in organelles. Both members of double cones had extensive subsurface cisternae along their contiguous surfaces. Cone inner segments changed little throughout the circadian cycle, suggesting an absence of significant retinomotor movements. Large, vesicular cone nuclei were located adjacent to or through the external limiting membrane. The cones' synaptic pedicles had larger synapses than rod spherules, with more of both invaginated (ribbon) and conventional (superficial) synaptic sites. Cone photoreceptors were arranged in a repeating square mosaic pattern with a single cone surrounded by four double (twin) cones. The photoreceptors of the Nile tilapia presented basic piscine characteristics, and also some more species-specific features.
研究了尼罗罗非鱼光适应和暗适应视网膜光感受器的结构和排列。将四只光适应和四只暗适应尼罗罗非鱼的眼睛常规固定，用于光学显微镜和透射电子显微镜观察。视杆细胞、单锥体细胞和双（孪生）锥体细胞的比例分别为30:1:2。光适应的视杆细胞较高，延伸至视网膜上皮层。视杆细胞内段显示远端线粒体椭球体，在肌样区域显著变窄。暗适应的视杆细胞内段短得多，肌样区域较厚，表明存在光机械运动。视杆细胞突触小球较小，有表面突触和内陷位点。单锥体细胞类似于双锥体细胞的单个成员。锥体细胞外段由带有单个切迹的均匀圆盘组成。所有锥体细胞都有一个短而逐渐变细的外段、一个大的线粒体椭球体和一个富含细胞器的肌样区域。双锥体细胞的两个成员在相邻表面都有广泛的表面下池。锥体细胞内段在整个昼夜周期变化不大，表明不存在明显的视网膜运动。大的泡状锥体细胞细胞核位于外部限制膜附近或穿过该膜。锥体细胞的突触小柄比视杆细胞小球有更大的突触，有更多的内陷（带状）和传统（表面）突触位点。锥体细胞光感受器以重复的方形镶嵌模式排列，单个锥体细胞被四个双（孪生）锥体细胞包围。尼罗罗非鱼的光感受器呈现出基本的鱼类特征，也有一些更具物种特异性的特征。
