Foster Russell G, Hankins Mark W
Department of Integrative and Molecular Neuroscience, Faculty of Medicine, Imperial College of Science, Engineering and Medicine, Charing Cross Hospital, Fulham Palace Road, W6 8RF, London, UK.
Prog Retin Eye Res. 2002 Nov;21(6):507-27. doi: 10.1016/s1350-9462(02)00036-8.
When reflected from a surface, light can provide a representation of the spatial environment, whilst gross changes in environment light can signal the time of day. The differing sensory demands of using light to detect environmental space and time appear to have provided the selection pressures for the evolution of different photoreceptor systems in the vertebrates, and probably all animals. This point has been well recognised in the non-mammals, which possess multiple opsin/vitamin A-based photoreceptor populations in a variety of sites distributed both within and outside the CNS. By contrast, eye loss in mammals abolishes all responses to light, and as a result, all photoreception was attributed to the rods and cones of the retina. However, studies over the past decade have provided overwhelming evidence that the mammalian eye contains a novel photoreceptor system that does not depend upon the input from the rods and cones. Mice with eyes but lacking rod and cone photoreceptors can still detect light to regulate their circadian rhythms, suppress pineal melatonin, modify locomotor activity, and modulate pupil size. Furthermore, action spectra for some of these responses in rodents and humans have characterised at least one novel opsin/vitamin A-based photopigment, and molecular studies have identified a number of candidate genes for this photopigment. Parallel studies in fish showing that VA opsin photopigment is expressed within sub-sets of inner retina neurones, demonstrates that mammals are not alone in having inner retinal photoreceptors. It therefore seems likely that inner retinal photoreception will be a feature of all vertebrates. Current studies are directed towards an understanding of their mechanisms, determining the extent to which they contribute to physiology and behaviour in general, and establishing how they may interact with other photoreceptors, including the rods and cones. Progress on each of these topics is moving very rapidly. As a result, we hope this review will serve as an introduction to the cascade of papers that will emerge on these topics in the next few years. We also hope to convince the more casual reader that there is much more to vertebrate photoreceptors than the study of retinal rods and cones.
当光线从一个表面反射时，它可以提供空间环境的表征，而环境光的总体变化可以指示一天中的时间。利用光线来检测环境空间和时间的不同感官需求，似乎为脊椎动物以及可能所有动物中不同光感受器系统的进化提供了选择压力。这一点在非哺乳动物中已得到充分认识，它们在中枢神经系统内外的各种部位拥有多种基于视蛋白/维生素A的光感受器群体。相比之下，哺乳动物失去眼睛会消除对光的所有反应，因此，所有光感受都归因于视网膜的视杆细胞和视锥细胞。然而，过去十年的研究提供了压倒性的证据，表明哺乳动物的眼睛含有一种不依赖视杆细胞和视锥细胞输入的新型光感受器系统。没有视杆细胞和视锥细胞光感受器但有眼睛的小鼠仍然可以检测光线来调节它们的昼夜节律、抑制松果体褪黑激素、改变运动活动并调节瞳孔大小。此外，啮齿动物和人类中这些反应的一些作用光谱已经表征了至少一种新型基于视蛋白/维生素A的光色素，分子研究已经确定了这种光色素的一些候选基因。在鱼类中的平行研究表明，VA视蛋白光色素在内视网膜神经元的子集中表达，这表明拥有内视网膜光感受器的并非只有哺乳动物。因此，内视网膜光感受似乎可能是所有脊椎动物的一个特征。目前的研究旨在了解它们的机制，确定它们在一般生理和行为中的贡献程度，并确定它们如何与其他光感受器相互作用，包括视杆细胞和视锥细胞。这些主题中的每一个都在迅速取得进展。因此，我们希望这篇综述将作为对未来几年将出现的关于这些主题的一系列论文的介绍。我们还希望说服更普通的读者，脊椎动物的光感受器不仅仅是对视网膜视杆细胞和视锥细胞的研究。
