Date Published: October 5, 2018
Publisher: Public Library of Science
Author(s): Fei Yao, Endong Zhang, Zhaolin Gao, Hongpei Ji, Mahmoud Marmouri, Xiaobo Xia, Alfred S Lewin.
Cholera toxin subunit B (CTB) and Fluorogold(FG) are two widely utilized retrograde tracers to assess the number and function of retinal ganglion cells (RGCs). However, the relative advantages and disadvantages of these tracers remain unclear, which may lead to their inappropriate application. In this study, we compared these tracers by separately injecting the tracer into the superior Colliculi (SC) in rats, one or 2 weeks later, the rats were sacrificed, and their retinas, brains, and optic nerves were collected. From the first to second week, FG displayed a greater number of labeled RGCs and a larger diffusion area in the SC than CTB; The number of CTB labeled RGCs and the diffusion area of CTB in the SC increased significantly, but there was no distinction between FG; Furthermore, CTB exhibited more labeled RGC neurites and longer neurites than FG, but no difference was evident between the same trace; The optic nerves labeled using CTB were much clearer than those labeled using FG. In conclusion, both CTB and FG can be used for the retrograde labeling of RGCs in rats at 1 or 2 weeks. FG achieves retrograde labeling of a greater number of RGCs than CTB, whereas CTB better delineates the morphology of RGCs. Furthermore, CTB seems more suitable for retrograde labeling of some small, non-image forming nuclei in the brain to which certain RGC subtypes project their axons.
Retinal ganglion cells (RGCs) are the main projecting retinal neurons in the visual pathway. They project their axons directly to the brain to perform image-forming and non-image forming functions, and they are the only afferent neurons from the retina [1–4].
Our study first comprehensively compared the differences between the two commonly used retrograde tracers, CTB and FG, in retrograde labeling of RGCs. In previous studies, many investigators prefer CTB for the retrograde labeling of RGCs because of its high efficiency: a relatively low concentration and low dose of CTB could achieve a satisfactory labeling effect . While Some researchers prefer FG for the retrograde labeling of RGCs because of its intense fluorescence, extensive filling of dendrites, high resistance to fading, and wide latitude of survival time [27, 37, 38]. However, up to now, no study has expressly indicated which tracer is more suitable for retrograde labeling RGCs.