Department of Neuroscience, College of Medicine, The Ohio State University, Columbus, Ohio, United States of America.
Department of Ophthalmology and Visual Science, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas, United States of America.
PLoS One. 2019 Aug 28;14(8):e0218818. doi: 10.1371/journal.pone.0218818. eCollection 2019.
Although it is well established that the vertebrate retina contains endogenous circadian clocks that regulate retinal physiology and function during day and night, the processes that the clocks affect and the means by which the clocks control these processes remain unresolved. We previously demonstrated that a circadian clock in the goldfish retina regulates rod-cone electrical coupling so that coupling is weak during the day and robust at night. The increase in rod-cone coupling at night introduces rod signals into cones so that the light responses of both cones and cone horizontal cells, which are post-synaptic to cones, become dominated by rod input. By comparing the light responses of cones, cone horizontal cells and rod horizontal cells, which are post-synaptic to rods, under dark-adapted conditions during day and night, we determined whether the daily changes in the strength of rod-cone coupling could account entirely for rhythmic changes in the light response properties of cones and cone horizontal cells. We report that although some aspects of the day/night changes in cone and cone horizontal cell light responses, such as response threshold and spectral tuning, are consistent with modulation of rod-cone coupling, other properties cannot be solely explained by this phenomenon. Specifically, we found that at night compared to the day the time course of spectrally-isolated cone photoresponses was slower, cone-to-cone horizontal cell synaptic transfer was highly non-linear and of lower gain, and the delay in cone-to-cone horizontal cell synaptic transmission was longer. However, under bright light-adapted conditions in both day and night, cone-to-cone horizontal cell synaptic transfer was linear and of high gain, and no additional delay was observed at the cone-to-cone horizontal cell synapse. These findings suggest that in addition to controlling rod-cone coupling, retinal clocks shape the light responses of cone horizontal cells by modulating cone-to-cone horizontal cell synaptic transmission.
虽然脊椎动物视网膜中存在内源性生物钟，这些生物钟在白天和夜间调节视网膜的生理和功能已得到充分证实，但生物钟影响的过程以及生物钟控制这些过程的方式仍未得到解决。我们之前的研究表明，金鱼视网膜中的生物钟调节视杆-视锥电耦联，使得在白天耦联较弱，而在夜间较强。夜间视杆-视锥耦联的增加将视杆信号引入视锥细胞，使得视锥细胞和视锥水平细胞（后者是视锥细胞的突触后细胞）的光反应都由视杆输入主导。通过比较在白天和夜间暗适应条件下视锥细胞、视锥水平细胞和视杆水平细胞（后者是视杆细胞的突触后细胞）的光反应，我们确定视杆-视锥耦联的日变化是否可以完全解释视锥细胞和视锥水平细胞光反应特性的节律变化。我们报告说，尽管视锥细胞和视锥水平细胞光反应的日/夜变化的某些方面，如反应阈值和光谱调谐，与视杆-视锥耦联的调制一致，但其他特性不能仅用这一现象来解释。具体来说，我们发现与白天相比，夜间光谱分离的视锥光反应的时程较慢，视锥-视锥水平细胞突触传递高度非线性且增益较低，并且视锥-视锥水平细胞突触传递的延迟较长。然而，在白天和夜间的强光适应条件下，视锥-视锥水平细胞突触传递是线性的且增益较高，并且在视锥-视锥水平细胞突触处没有观察到额外的延迟。这些发现表明，除了控制视杆-视锥耦联之外，视网膜时钟还通过调节视锥-视锥水平细胞突触传递来塑造视锥水平细胞的光反应。
