光和暗对埃及蟾蜍(BUFO REGULARIS)发育中的视网膜的影响(英文)

本文研究了埃及蟾蜍(Bufo regularis Reuss)从早期幼虫到变态结束,光和暗对视网膜的影响。所观察到的对光和暗反应的变化限于色素上皮和光感受细胞。实验动物分四组:1)在亮处固定的对照(CL);2)在暗处固定的对照(CD);3)连续养在暗处的动物(DD);4)连续受光照的动物(LL)。在CD和DD组动物,黑色素颗粒在色素上皮细胞突起(PEP)中的分布限于光感受细胞顶部间之外周区(巩膜方位)。与此相反。在CL和LL组动物,大量黑色素颗粒则分散在视觉细胞外节段和椭球段间色素上皮细胞突起之向心端位置(玻璃体方位)。在这种动物,上皮细胞色素对光和暗反应发生的光机械运动出现在肢芽期以前。新变态小蟾蜍DD组眼球,与其他三组比较起来,色素上皮层相当厚并含有大的脂肪滴。在较晚期,只有DD组动物的一些杆细胞外节段呈现退化现象。其次,这一组中,由于连续缺少光照的结果,眼球之锥细胞数目有明显减少。四组动物的视网膜上也观察到锥细胞的细胞核位置略有不同。

EFFECT OF LIGHT AND DARK ON THE DEVELOPING RETINA OF THE EGYPTIAN TOAD, BUFO REGULARIS

The effect of light and dark on the retina of the Egyptian toad, Bufo regularis Reuss, was studied during its development from early larval stages till the end of metamorphosis. The observed changes in response to light and dark were restricted to the pigment epithelium and the photo-receptor cells. The animals examined were divided into four groups: 1-controls fixed in light (CL); 2-controls fixed in dark (CD); 3-animals maintained under continuous darkness (DD): and 4-animals exposed to continuous lighting (LL). In CD-and DD-animals, the location of melanin granules in the pigment epithelial processes (PEP) was restricted to the peripheral area between the apical portions of photoreceptor cells (scleral position). In CL-and LL-animals, on the contrary, abundant melanin granules were found in the PEP where they were dispersed more centripetally between the outer segments and ellipsoids of the visual cells (vitreal position). Photomechanical movements of the epithelial pigments were indicated in this species in response to light and dark before reaching the limb-bud stage. In DD-eye of the newly metamorphosed toadlets, the pigment epithelium appeared considerably thick and containd large lipid droplets when compared to that of the other three groups. Only in DD-animals some rod outer segments showed degeneration during the later stages of development. In addition, there was a remarkable reduction in the number of cones in the eyes of this group as a result of continuous light deprivation. Some differences in the position of cone nuclei were also observed in the retinae of the four groups.