Institute of Neurobiology, Institutes of Brain Science, Fudan University, Shanghai, PR China.
Prog Retin Eye Res. 2013 Jan;32:64-87. doi: 10.1016/j.preteyeres.2012.07.003. Epub 2012 Aug 16.
The neurohormone melatonin is implicated in a variety of physiological processes. In the retina, a major source for melatonin production, melatonin is involved in modulation of neuronal activities. In this article we review recent advances in this research field, which is preceded by a concise account of general information about melatonin, melatonin receptors and intracellular signaling pathways for melatonin actions. Melatonin is mainly synthesized in and released from photoreceptors in the retina. Different subtypes of melatonin receptors are present on major types of retinal neurons, and the expression of these receptors is highly species- and neuron subtype-dependent. By activating different melatonin receptor subtypes, melatonin modulates activities of retinal neurons. In the outer retina, melatonin regulates the activity of photoreceptors. In addition, melatonin reduces the light responsiveness of cone-driven horizontal cells, but potentiates rod signal to rod-dominant ON type bipolar cells in teleost fish or inhibits the TEA-sensitive potassium channel of rod-driven ON type bipolar cells in rats. In the inner retina, melatonin potentiates inputs from glycinergic amacrine cells to ganglion cells in rats. These actions of melatonin on retinal neurons are mediated by distinct intracellular signaling pathways via different subtypes of melatonin receptors and all serve to improve visual performance in a world of changing ambient illumination. The topics, concerning allosteric action of melatonin, interplay between melatonin and dopamine systems, and potential interaction between melatonin and melanopsin systems, are also discussed. An in-depth discussion of future directions in this research field is presented.
神经激素褪黑素参与多种生理过程。在视网膜中，褪黑素的主要产生部位，参与调节神经元活动。本文综述了该研究领域的最新进展，首先简要介绍了褪黑素的一般信息、褪黑素受体和褪黑素作用的细胞内信号通路。褪黑素主要在视网膜中的感光细胞中合成并释放。不同亚型的褪黑素受体存在于主要类型的视网膜神经元上，这些受体的表达高度依赖于物种和神经元亚型。通过激活不同的褪黑素受体亚型，褪黑素调节视网膜神经元的活性。在外视网膜中，褪黑素调节光感受器的活性。此外，褪黑素降低了视锥细胞驱动的水平细胞的光反应性，但在硬骨鱼中增强了视杆信号向视杆主导的 ON 型双极细胞的作用，或在大鼠中抑制视杆驱动的 ON 型双极细胞的 TEA 敏感钾通道。在内视网膜中，褪黑素增强了大鼠中甘氨酸能无长突细胞向神经节细胞的输入。褪黑素对视网膜神经元的这些作用是通过不同亚型的褪黑素受体通过不同的细胞内信号通路介导的，所有这些作用都有助于在不断变化的环境光照下改善视觉性能。本文还讨论了褪黑素的变构作用、褪黑素与多巴胺系统的相互作用以及褪黑素与黑视蛋白系统的潜在相互作用等相关话题。对该研究领域未来方向进行了深入讨论。
