Neuromuscular Control of Primate Eye Movements

分析视觉世界需要两只眼睛的细致协调，这是由六块肌肉实现的， 围绕着每一只眼睛。在脑干运动神经元的控制下，这些肌肉快速移动眼睛， 目标（使用扫视）或跟踪它们（平滑追踪）。肌肉也会做出缓慢的调整， 正确的双眼深度对齐（聚散），并保持眼睛静止以进行目标检查（固定）。共同 视觉障碍如斜视是由这种神经肌肉系统的异常引起的。电流 治疗可以减轻症状，但不能解决根本问题。为了治疗 我们需要更多地了解神经肌肉回路的细节。长期以来， 眼外肌纤维有两种主要类型：多神经支配纤维（MIFs）， 沿着它们的整个长度接受许多神经肌肉接头，以及单神经纤维（SIF）， 在它们的中间区域接受一条神经肌肉接头带。最近在灵长类动物中发现 这两种类型的肌纤维由不同的运动神经元群提供，揭示了MIF与 SIF的区别延伸到完整的运动单位。MIFs及其运动神经元的解剖学特征表明 它们控制缓慢的双眼对准（聚散和固定），而SIF及其运动神经元控制 更快，目标运动（扫视和平滑的追求）。总的目标是测试这个假设的双重- 眼睛的运动控制。这将使用线性阵列记录和光遗传学来研究MIF 和SIF运动神经元。初步研究表明，猕猴的眼外运动神经元可以 病毒转导以表达外源基因，为光遗传学方法奠定了基础。第一个目标是 在猕猴运动神经元中实现可靠、稳健的病毒转导和视蛋白表达。三种病毒载体 将以不同的体积和滴度注射到眼眶肌肉中。转基因表达 将在注射后1年内对运动神经元（沿着任何神经毒性证据）进行组织学分析 以确定最佳参数。第二个目的是区分多边投资基金和战略投资基金的职能作用 运动神经元利用灵长类动物眼内MIF和SIF运动神经元的分离共线位置 核，我们将角度线性阵列电极同时采样两个群体。运动神经元活动 将被分析的聚散，眼跳，和顺利的追求运动的猕猴。MIF 运动神经元将用体内光遗传学光标记和组织学分析来鉴定。的结果 这项研究将解决MIF和SIF运动单元是否构成一个双运动系统来控制 眼睛如果像预测的那样，MIF子系统专门用于双目对准，那么它将被暗示为一个位点 这为治疗提供了一个特定的目标。更一般地说，这项工作将提供新的 研究灵长类运动神经元的病毒和神经生理学技术，建立了一个新的灵长类运动神经元实验平台， 光遗传学，并告知神经肌肉疾病基因治疗的安全性和有效性。

Analyzing the visual world requires the meticulous coordination of both eyes, achieved by six muscles that surround each eye. Controlled by motoneurons in the brainstem, these muscles move the eyes rapidly to acquire targets (using saccades) or track them (smooth pursuit). The muscles also make slower adjustments to maintain proper binocular alignment in depth (vergence) and keep the eyes still for target inspection (fixation). Common visuomotor disorders such as strabismus result from abnormalities in this neuromuscular system. Current treatments mitigate symptoms, but do not fix the underlying problems. To progress toward cures for the disorders, we need to learn more about the details of the neuromuscular circuits. A longstanding curiosity about extraocular muscle fibers has been that they come in two major types: multiply-innervated fibers (MIFs) that receive numerous neuromuscular junctions along their entire length, and singly-innervated fibers (SIFs) that receive a single band of neuromuscular junctions in their middle region. It was discovered recently in primates that these two types of muscle fibers are supplied by distinct groups of motoneurons, revealing that the MIF vs. SIF distinction extends to full motor units. Anatomical characteristics of MIFs and their motoneurons suggest they control slow, binocular alignment (vergence and fixation) whereas SIFs and their motoneurons control faster, targeting movements (saccades and smooth pursuit). The overall goal is to test this hypothesis of dual- motor control of the eyes. This will be accomplished using linear array recordings and optogenetics to study MIF and SIF motoneurons in behaving macaques. Pilot work showed that macaque extraocular motoneurons can be virally transduced to express exogenous genes, setting the stage for the optogenetic approach. The first aim is to achieve reliable, robust viral transduction and opsin expression in macaque motoneurons. Three viral vectors will be injected into orbital muscles at varying volumes and titers. Consequent transgene expression in motoneurons, along with any evidence of neurotoxicity, will be analyzed histologically up to 1 year post-injection to determine optimal parameters. The second aim is to distinguish the functional roles of MIF and SIF motoneurons. Exploiting the separate, colinear locations of MIF and SIF motoneurons in the primate oculomotor nucleus, we will angle linear array electrodes to sample both populations simultaneously. Motoneuron activity will be analyzed in relation to vergence, saccade, and smooth pursuit movements made by the macaques. MIF motoneurons will be identified with in vivo optogenetic phototagging and histological analyses. The outcome of the study will be to resolve whether MIF and SIF motor units constitute a dual-motor system for controlling the eyes. If the MIF subsystem is specialized for binocular alignment, as predicted, it would be implicated as a locus of disruption in strabismus, providing a specific target for treatment. More generally, the work will provide new viral and neurophysiological techniques for studying primate motoneurons, establish a novel testbed for primate optogenetics, and inform the safety and efficacy of gene therapy for neuromuscular disorders.