Udoh Uwemedimo G, Zheng Kaiyuan, Bruno John R, Hunt Jasper E, Pratt Kara G
Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, USA.
Program in Neuroscience, University of Wyoming, Laramie, Wyoming, USA.
Dev Neurobiol. 2025 Jul;85(3):e22968. doi: 10.1002/dneu.22968.
The retinotectal projection, the direct synapse between retinal ganglion cells (RGCs) of the eye and tectal neurons of the optic tectum, is a major component of the amphibian visual system. A model of circuit formation, this projection has been studied in detail. There are, however, other retinorecipient targets that also comprise the amphibian visual system such as the pretectum and ventral midbrain tegmentum. Understanding how these other components of the visual system form and function will lead to a more comprehensive understanding of how the visual system, as a whole, assembles and functions. Toward this aim, here we describe the functional development of the Xenopus tadpole accessory optic system (AOS), a direct synaptic connection between RGC axons and the basal optic nucleus of the midbrain tegmentum. The AOS is highly conserved across vertebrates. It functions as the sensory side of the optokinetic and optomotor reflexes, compensatory eye and body movements, respectively, that stabilize the visual scene as the organism moves through it. Using an isolated brain preparation and whole-cell electrophysiological approaches, we compared the development of the AOS and retinotectal projection. We found that these two retinofugal projections display distinct developmental programs, which appear to mirror their different functions. Retinotectal synapses moved through a dynamic phase of previously described NMDA receptor-dependent refinement, a process that is known to sharpen the retinotopic map and thereby visual acuity. In contrast, the AOS synapse appeared more stable and activity independent across development, indicative of a hardwired circuit, built to support reflexive optic behaviors.
视网膜顶盖投射是眼睛的视网膜神经节细胞（RGCs）与视顶盖的顶盖神经元之间的直接突触，是两栖动物视觉系统的主要组成部分。作为一种神经回路形成模型，该投射已得到详细研究。然而，两栖动物视觉系统还包括其他接受视网膜传入的靶点，如顶盖前区和腹侧中脑被盖。了解视觉系统的这些其他组成部分如何形成和发挥功能，将有助于更全面地理解整个视觉系统是如何组装和运作的。为了实现这一目标，我们在此描述非洲爪蟾蝌蚪附属视觉系统（AOS）的功能发育，它是RGC轴突与中脑被盖基部视核之间的直接突触连接。AOS在脊椎动物中高度保守。它分别作为视动反射和视运动反射的感觉部分，即补偿性眼球和身体运动，在生物体移动时稳定视觉场景。我们使用离体脑标本和全细胞膜片钳电生理方法，比较了AOS和视网膜顶盖投射的发育过程。我们发现这两种视网膜传出投射表现出不同的发育程序，这似乎反映了它们不同的功能。视网膜顶盖突触经历了一个先前描述的依赖N-甲基-D-天冬氨酸（NMDA）受体的精细化动态阶段，这一过程已知会锐化视网膜拓扑图，从而提高视敏度。相比之下，AOS突触在整个发育过程中显得更加稳定且不依赖活动，这表明它是一个硬连线回路，旨在支持反射性视觉行为。
