Barta C L, Thoreson W B
Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA.
Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198, USA.
IBRO Neurosci Rep. 2024 Jul 21;17:138-144. doi: 10.1016/j.ibneur.2024.07.003. eCollection 2024 Dec.
Optomotor responses are a popular way to assess sub-cortical visual responses in mice. We studied photoreceptor inputs into optomotor circuits using genetically-modified mice lacking the exocytotic calcium sensors synaptotagmin 1 (Syt1) and 7 (Syt7) in rods or cones. We also tested mice that in which cone transducin, GNAT2, had been eliminated. We studied spatial frequency sensitivity under mesopic conditions by varying the spatial frequency of a grating rotating at 12 deg/s and contrast sensitivity by varying luminance contrast of 0.2c/deg gratings. We found that eliminating Syt1 from rods reduced responses to a low spatial frequency grating (0.05c/deg) consistent with low resolution in this pathway. Conversely, eliminating the ability of cones to respond to light (by eliminating GNAT2) or transmit light responses (by selectively eliminating Syt1) showed weaker responses to a high spatial frequency grating (3c/deg). Eliminating Syt7 from the entire optomotor pathway in a global knockout had no significant effect on optomotor responses. We isolated the secondary rod pathway involving transmission of rod responses to cones via gap junctions by simultaneously eliminating Syt1 from rods and GNAT2 from cones. We found that the secondary rod pathway is sufficient to drive robust optomotor responses under mesopic conditions. Finally, eliminating Syt1 from both rods and cones almost completely abolished optomotor responses, but we detected weak responses to large, bright rotating gratings that are likely driven by input from intrinsically photosensitive retinal ganglion cells.
视动反应是评估小鼠皮层下视觉反应的一种常用方法。我们使用在视杆或视锥细胞中缺乏胞吐钙传感器突触结合蛋白1（Syt1）和7（Syt7）的转基因小鼠，研究了视杆和视锥细胞向视动回路的光感受器输入。我们还测试了视锥转导蛋白GNAT2已被消除的小鼠。我们通过改变以12°/秒旋转的光栅的空间频率，研究了在中间视觉条件下的空间频率敏感性，并通过改变0.2c/度光栅的亮度对比度来研究对比度敏感性。我们发现，从视杆细胞中消除Syt1会降低对低空间频率光栅（0.05c/度）的反应，这与该通路中的低分辨率一致。相反，消除视锥细胞对光的反应能力（通过消除GNAT2）或传递光反应的能力（通过选择性消除Syt1）会导致对高空间频率光栅（3c/度）的反应减弱。在全局基因敲除中从整个视动通路中消除Syt7对视动反应没有显著影响。我们通过同时从视杆细胞中消除Syt1和从视锥细胞中消除GNAT2，分离出了涉及视杆细胞反应通过缝隙连接传递到视锥细胞的次级视杆通路。我们发现，次级视杆通路足以在中间视觉条件下驱动强烈的视动反应。最后，从视杆细胞和视锥细胞中都消除Syt1几乎完全消除了视动反应，但我们检测到对大的、明亮的旋转光栅的微弱反应，这些反应可能是由内在光敏性视网膜神经节细胞的输入驱动的。
