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 two 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 ~5% of the ganglion cells that project to the lateral geniculate nucleus. Surprisingly, there exist no ganglion cells that project exclusively to the SC.

上丘接受视网膜神经节细胞的直接投射。在灵长类动物中，相同的神经节细胞是否也供应外侧膝状核仍然未知。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。动物固定一个靶点，同时通过记录和用四极管刺激在上丘中侦察注射部位。一旦确定了合适的部位，就通过相邻的微量移液器注射霍乱毒素亚基 B-Alexa Fluor 488。在随后的急性实验中，将霍乱毒素亚基 B-Alexa Fluor 555 注射到匹配的视网膜位置外侧膝状核中。短暂的存活期后，在视网膜平装中检查神经节细胞。双标记细胞的百分比在局部变化，具体取决于每个示踪剂逆行转运的相对效率以及每个靶核中注射部位视网膜重叠的精度。在具有广泛重叠的计数框中，76-98% 的突出到上丘的神经节细胞被双重标记。突出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，有 5,746 个细胞仅被 CTB-AF555 标记，561 个细胞被 CTB-AF555 和 CTB-AF488 双重标记，但没有细胞仅被 CTB-AF488 标记。这些数据表明，猕猴上丘的视网膜输入来自由 ~5% 的神经节细胞提供的侧支轴突支，该神经节细胞投射到外侧膝状核。令人惊讶的是，不存在专门投射到 SC 的神经节细胞。