Department of Neurobiology and Anatomy, McGovern Medical School, Houston, TX, USA.
Department of Ophthalmology, University of Washington, Seattle, WA, USA.
Sci Rep. 2022 Sep 7;12(1):15160. doi: 10.1038/s41598-022-19324-z.
Ganglion cells are the projection neurons of the retina. Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and also receive input from rods and cones via bipolar cells and amacrine cells. In primates, multiple types of ipRGCs have been identified. The ipRGCs with somas in the ganglion cell layer have been studied extensively, but less is known about those with somas in the inner nuclear layer, the "displaced" cells. To investigate their synaptic inputs, three sets of horizontal, ultrathin sections through central macaque retina were collected using serial block-face scanning electron microscopy. One displaced ipRGC received nearly all of its excitatory inputs from ON bipolar cells and would therefore be expected to have ON responses to light. In each of the three volumes, there was also at least one cell that had a large soma in the inner nuclear layer, varicose axons and dendrites with a large diameter that formed large, extremely sparse arbor in the outermost stratum of the inner plexiform layer. They were identified as the displaced M1 type of ipRGCs based on this morphology and on the high density of granules in their somas. They received extensive input from amacrine cells, including the dopaminergic type. The vast majority of their excitatory inputs were from OFF bipolar cells, including two subtypes with extensive input from the primary rod pathway. They would be expected to have OFF responses to light stimuli below the threshold for melanopsin or soon after the offset of a light stimulus.
神经节细胞是视网膜的投射神经元。固有光敏感视网膜神经节细胞 (ipRGC) 表达光色素黑视蛋白，并通过双极细胞和无长突细胞接收来自视杆和视锥细胞的输入。在灵长类动物中，已经鉴定出多种类型的 ipRGC。位于神经节细胞层中的 ipRGC 体已被广泛研究，但对于位于内核层中的“移位”细胞的了解较少。为了研究它们的突触输入，使用连续块面扫描电子显微镜收集了三组穿过中央猕猴视网膜的水平超薄切片。一个移位的 ipRGC 几乎接收了所有来自 ON 双极细胞的兴奋性输入，因此预计对光有 ON 反应。在三个体积中，至少还有一个细胞在内核层中有一个大的体，有迂曲的轴突和直径较大的树突，在外丛状层的最外层形成大而极其稀疏的树突。基于这种形态学以及它们体中的颗粒高密度，它们被鉴定为移位的 M1 型 ipRGC。它们从无长突细胞接收广泛的输入，包括多巴胺能型。它们的绝大多数兴奋性输入来自 OFF 双极细胞，包括两种来自主要视杆途径的广泛输入的亚型。它们预计对低于黑视蛋白阈值或在光刺激消退后不久的光刺激有 OFF 反应。
