Manglapus M K, Iuvone P M, Underwood H, Pierce M E, Barlow R B
Center for Vision Research, Department of Ophthalmology, State University of New York Health Science Center, Syracuse, New York 13210, USA.
J Neurosci. 1999 May 15;19(10):4132-41. doi: 10.1523/JNEUROSCI.19-10-04132.1999.
A circadian clock modulates the functional organization of the Japanese quail retina. Under conditions of constant darkness, rods dominate electroretinogram (ERG) b-wave responses at night, and cones dominate them during the day, yielding a circadian rhythm in retinal sensitivity and rod-cone dominance. The activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, also exhibits a circadian rhythm in the retina with approximately threefold higher levels during the day than at night. The rhythm of tyrosine hydroxylase activity is opposite in phase to the circadian activity of tryptophan hydroxylase, the first enzyme in the melatonin biosynthetic pathway. We tested whether dopamine may be related to the physiological rhythms of the retina by examining the actions of pharmacological agents that effect dopamine receptors. We found that blocking dopamine D2 receptors in the retina during the day mimics the nighttime state by increasing the amplitude of the b-wave and shifting the retina to rod dominance. Conversely, activating D2 receptors at night mimics the daytime state by decreasing the amplitude of the b-wave and shifting the retina to cone dominance. A selective antagonist for D1 dopamine receptors has no effect on retinal sensitivity or rod-cone dominance. Reducing retinal dopamine partially abolishes rhythms in sensitivity and yields a rod-dominated retina regardless of the time of day. These results suggest that dopamine, under the control of a circadian oscillator, has a key role in modulating sensitivity and rod-cone dominance in the Japanese quail retina.
昼夜节律时钟调节日本鹌鹑视网膜的功能组织。在持续黑暗的条件下，夜间视网膜电图（ERG）的b波反应以视杆细胞为主，而白天则以视锥细胞为主，从而产生视网膜敏感度和视杆 - 视锥细胞主导性的昼夜节律。酪氨酸羟化酶是多巴胺合成中的限速酶，其活性在视网膜中也呈现昼夜节律，白天的水平比夜间高约三倍。酪氨酸羟化酶活性的节律与褪黑素生物合成途径中的第一种酶色氨酸羟化酶的昼夜活性相位相反。我们通过研究影响多巴胺受体的药物制剂的作用，来测试多巴胺是否可能与视网膜的生理节律有关。我们发现，白天阻断视网膜中的多巴胺D2受体会增加b波振幅并使视网膜转变为视杆细胞主导，从而模拟夜间状态。相反，夜间激活D2受体则会降低b波振幅并使视网膜转变为视锥细胞主导，从而模拟白天状态。D1多巴胺受体的选择性拮抗剂对视网膜敏感度或视杆 - 视锥细胞主导性没有影响。减少视网膜多巴胺会部分消除敏感度的节律，并且无论白天的时间如何，都会产生以视杆细胞为主的视网膜。这些结果表明，在昼夜振荡器的控制下，多巴胺在调节日本鹌鹑视网膜的敏感度和视杆 - 视锥细胞主导性方面具有关键作用。
