School of Veterinary Medicine and Biomedical Sciences, University of Nebraska, Lincoln, NE 68583, USA.
Rev Physiol Biochem Pharmacol. 2012;162:59-90. doi: 10.1007/112_2011_4.
Intrinsically photosensitive retinal ganglion cells (ipRGCs) respond to light in the absence of all rod and cone photoreceptor input. The existence of these ganglion cell photoreceptors, although predicted from observations scattered over many decades, was not established until it was shown that a novel photopigment, melanopsin, was expressed in retinal ganglion cells of rodents and primates. Phototransduction in mammalian ipRGCs more closely resembles that of invertebrate than vertebrate photoreceptors and appears to be mediated by transient receptor potential channels. In the retina, ipRGCs provide excitatory drive to dopaminergic amacrine cells and ipRGCs are coupled to GABAergic amacrine cells via gap junctions. Several subtypes of ipRGC have been identified in rodents based on their morphology, physiology and expression of molecular markers. ipRGCs convey irradiance information centrally via the optic nerve to influence several functions including photoentrainment of the biological clock located in the hypothalamus, the pupillary light reflex, sleep and perhaps some aspects of vision. In addition, ipRGCs may also contribute irradiance signals that interface directly with the autonomic nervous system to regulate rhythmic gene activity in major organs of the body. Here we review the early work that provided the motivation for searching for a new mammalian photoreceptor, the ground-breaking discoveries, current progress that continues to reveal the unusual properties of these neuron photoreceptors, and directions for future investigation.
内在光敏视网膜神经节细胞（ipRGCs）在没有所有视杆和视锥感光细胞输入的情况下对光产生反应。这些神经节细胞光感受器的存在，尽管从几十年来分散的观察中预测到，但直到证明一种新型光色素视黑质在啮齿动物和灵长类动物的视网膜神经节细胞中表达后才得到证实。哺乳动物 ipRGC 中的光传导更类似于无脊椎动物而不是脊椎动物感光器，并且似乎由瞬时受体电位通道介导。在视网膜中，ipRGC 向多巴胺能无长突细胞提供兴奋性驱动，并且 ipRGC 通过缝隙连接与 GABA 能无长突细胞偶联。基于形态、生理学和分子标记物的表达，已经在啮齿动物中鉴定出几种 ipRGC 亚型。ipRGC 通过视神经向中枢传递辐照度信息，从而影响几种功能，包括位于下丘脑的生物钟的光刺激、瞳孔对光反射、睡眠，也许还有一些视觉方面的功能。此外，ipRGC 还可能直接与自主神经系统接口传递辐照度信号，以调节身体主要器官的节律性基因活性。在这里，我们回顾了早期的工作，这些工作为寻找新型哺乳动物感光器提供了动力，介绍了开创性的发现、当前的进展，这些进展继续揭示了这些神经元感光器的异常特性，并为未来的研究提供了方向。
