Thoreson Wallace B, Sladek Asia L, Barta Cody L, Townsend Lou E
Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE 68106, USA.
Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68106, USA.
bioRxiv. 2024 Oct 31:2024.10.30.621116. doi: 10.1101/2024.10.30.621116.
Rod and cone photoreceptor cells selectively contact different compartments of axon-bearing retinal horizontal cells in the retina. Cones synapse exclusively on the soma whereas rods synapse exclusively on a large axon terminal compartment. The possibility that rod signals can travel down the axon from terminal to soma has been proposed to allow spectrally opponent interactions between rods and cones, but there is conflicting data about whether this actually occurs. Because of spectral overlap between rod and cone visual pigments in mouse, we analyzed photoreceptor inputs into horizontal somata by selectively expressing channelrhodopsin in rods and/or cones. Optogenetic stimulation of rods and cones both evoked large fast inward currents in horizontal cell somata. Cone-driven responses were abolished by eliminating synaptic release in a cone-specific knockout of the exocytotic calcium sensor, synaptotagmin 1. However, rod-driven responses in horizontal somata were unchanged after eliminating synaptic release from rods but abolished by eliminating release from both rods and cones. This suggests that cones transmit rod signals that arrive via rod-cone gap junctions. Consistent with this, eliminating Cx36 gap junctions between rods and cones also abolished rod-driven optogenetic responses in horizontal cell somata. These results show that rod signals reach the somas of B-type horizontal cells exclusively via gap junctions with cones and not by traveling down the axon from the axon terminal.
视杆和视锥光感受器细胞在视网膜中选择性地与带有轴突的视网膜水平细胞的不同部分相接触。视锥仅与胞体形成突触，而视杆仅与一个大的轴突终末部分形成突触。有人提出视杆信号可以从终末沿着轴突向下传导至胞体，从而实现视杆和视锥之间的光谱拮抗相互作用，但关于这种情况是否实际发生，存在相互矛盾的数据。由于小鼠视杆和视锥视觉色素之间存在光谱重叠，我们通过在视杆和/或视锥中选择性表达通道视紫红质，分析了光感受器对水平细胞胞体的输入。对视杆和视锥的光遗传学刺激均在水平细胞胞体中诱发了大的快速内向电流。在视锥特异性敲除胞吐钙传感器突触结合蛋白1以消除突触释放后，视锥驱动的反应消失。然而，在消除视杆的突触释放后，水平细胞胞体中视杆驱动的反应并未改变，但在同时消除视杆和视锥的释放后则消失。这表明视锥传递通过视杆 - 视锥间隙连接到达的视杆信号。与此一致的是，消除视杆和视锥之间的Cx36间隙连接也消除了水平细胞胞体中视杆驱动的光遗传学反应。这些结果表明，视杆信号仅通过与视锥的间隙连接到达B型水平细胞的胞体，而不是从轴突终末沿着轴突向下传导。
