Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2010 Mar 30;107(13):6034-9. doi: 10.1073/pnas.0914718107. Epub 2010 Mar 11.
Darkness serves as a stimulus for vertebrate photoreceptors; they are actively depolarized in the dark and hyperpolarize in the light. Here, we show that larval zebrafish essentially turn off their visual system at night when they are not active. Electroretinograms recorded from larval zebrafish show large differences between day and night; the responses are normal in amplitude throughout the day but are almost absent after several hours of darkness at night. Behavioral testing also shows that larval zebrafish become unresponsive to visual stimuli at night. This phenomenon is largely circadian driven as fish show similar dramatic changes in visual responsiveness when maintained in continuous darkness, although light exposure at night partially restores the responses. Visual responsiveness is decreased at night by at least two mechanisms: photoreceptor outer segment activity decreases and synaptic ribbons in cone pedicles disassemble.
黑暗是脊椎动物光感受器的刺激源；在黑暗中，它们会被主动去极化，在光下则会超极化。在这里，我们表明，当幼鱼不活跃时，它们在夜间基本上会关闭视觉系统。从幼鱼中记录的视网膜电图显示出白天和黑夜之间的巨大差异；白天的反应幅度正常，但在夜间几个小时的黑暗后几乎不存在。行为测试也表明，幼鱼在夜间对视觉刺激无反应。这种现象主要是由昼夜节律驱动的，因为即使在连续黑暗中，鱼类也会表现出类似的视觉反应的显著变化，尽管夜间的光照会部分恢复这些反应。至少有两种机制会导致夜间的视觉反应性降低：光感受器外节的活动减少和视锥神经节内的突触小带解体。
