The superior colliculus receives a direct projection from retinal ganglion cells. In primates, it remains unknown if the same ganglion cells also supply the lateral geniculate nucleus. To address this issue, a double-label experiment was performed in 2 male macaques. The animals fixated a target while injection sites were scouted in the superior colliculus by recording and stimulating with a tetrode. Once suitable sites were identified, cholera toxin - subunit B Alexa Fluor 488 was injected via an adjacent micropipette. In a subsequent acute experiment, cholera toxin subunit B - Alexa Fluor 555 was injected into the lateral geniculate nucleus at matching retinotopic locations. After a brief survival period, ganglion cells were examined in retinal flatmounts. The percentage of double-labeled cells varied locally, depending on the relative efficiency of retrograde transport by each tracer and the precision of retinotopic overlap of injection sites in each target nucleus. In counting boxes with extensive overlap, 76-98% of ganglion cells projecting to the superior colliculus were double-labeled. Cells projecting to the superior colliculus constituted 4.0 - 6.7% of the labeled ganglion cell population. In one particularly large zone, there were 5,746 cells labeled only by CTB-AF555, 561cells double-labeled by CTB-AF555 and CTB-AF488, but no cell labeled only by CTB-AF488. These data indicate that retinal input to the macaque superior colliculus arises from a collateral axonal branch supplied by about 5% of the ganglion cells that project to the lateral geniculate nucleus. Surprisingly, there exist no ganglion cells that project exclusively to the SC.Significance statement The retina contains a multitude of ganglion cell classes, projecting in parallel to different brain targets. The superior colliculus receives retinal input, but its source remains controversial. In two macaques, a green tracer was injected into the superior colliculus and an orange tracer into the lateral geniculate nucleus. When retinotopic overlap was optimal, ganglion cells containing the green tracer were also labeled by the orange tracer. This finding indicates that retinal input to the superior colliculus arises from axon collaterals of ganglion cells that project to the lateral geniculate nucleus, even though these two retinal targets serve utterly different functions. The next challenge is to determine the purpose of this projection and why it is shared.

中文翻译：

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猕猴上丘的视网膜输入源自投射到外侧膝状核的分支轴突。


上丘接受视网膜神经节细胞的直接投射。在灵长类动物中，尚不清楚相同的神经节细胞是否也提供外侧膝状核。为了解决这个问题，在两只雄性猕猴身上进行了双标签实验。动物固定目标，同时通过四极管记录和刺激在上丘中寻找注射部位。一旦确定了合适的位点，霍乱毒素 - 亚基 B Alexa Fluor 488 通过相邻的微量移液器注射。在随后的急性实验中，霍乱毒素亚基 B​​ - Alexa Fluor 555 被注射到外侧膝状核中匹配的视网膜专题位置。经过短暂的存活期后，在视网膜平板上检查神经节细胞。双标记细胞的百分比局部变化，取决于每种示踪剂逆行运输的相对效率以及每个靶核中注射位点的视网膜专题重叠的精度。在具有广泛重叠的计数盒中，76-98% 投射到上丘的神经节细胞是双标记的。投射到上丘的细胞占标记神经节细胞群的 4.0 - 6.7%。在一个特别大的区域中，仅用CTB-AF555标记的细胞有5,746个，用CTB-AF555和CTB-AF488双标记的细胞有561个，但没有仅用CTB-AF488标记的细胞。这些数据表明，猕猴上丘的视网膜输入来自侧支轴突分支，该侧支轴突分支由投射到外侧膝状核的神经节细胞的约 5% 提供。令人惊讶的是，不存在专门投射到 SC 的神经节细胞。意义陈述 视网膜包含多种神经节细胞类别，平行投射到不同的大脑目标。上丘接收视网膜输入，但其来源仍然存在争议。在两只猕猴中，将绿色示踪剂注入上丘，将橙色示踪剂注入外侧膝状核。当视网膜专题重叠达到最佳时，含有绿色示踪剂的神经节细胞也被橙色示踪剂标记。这一发现表明，视网膜对上丘的输入来自投射到外侧膝状核的神经节细胞的轴突侧枝，尽管这两个视网膜目标具有完全不同的功能。下一个挑战是确定该预测的目的以及共享该预测的原因。