MIDBRAIN CIRCUITRY FOR NEURONAL CONTROL OF GAZE

描述（由申请方提供）：本研究研究了眼周区域的神经元回路，其有助于近距离反应和眼定向的组成部分，并且在斜视和弱视的病因学中可能很重要。目的是确定运动前输入到控制透镜和瞳孔的节前副交感神经运动神经元，以及控制眼外肌中的多神经支配肌纤维（MIFs）的运动神经元。MIFs具有高度的抗疲劳性和强直活性。它们帮助调整滑轮系统，并与栅栏末端相关，可能有助于眼部本体感受。因此，它们可能在控制正常的眼睛方向和斜视中的眼睛错位中起作用。神经节前和MIF运动神经元群位于眼周区域。该区域还包含中间神经元，包括那些利用神经肽尿皮质素的中间神经元，尿皮质素被认为在应激行为中起作用。为了确定控制眼外肌中的透镜、瞳孔和MIF纤维的电路，我们必须确定每个纤维的运动前输入。所提出的实验将确定这些元素中的哪一个是眼周区域的三个已知输入的目标：中央中脑网状结构（cMRF），其可以包含扫视相关和聚散相关神经元，顶核，其被认为以适应性方式调节近三联体反应，以及上级丘，其在扫视眼球运动中具有众所周知的作用，但也可能在近期反应中发挥作用。该提案包含在猕猴中进行的4个相互关联的神经解剖学目标。他们的特点是结合了联合收割机顺行示踪剂与逆行或免疫组织化学细胞鉴定的实验，并具有LM和EM分析。目的1是确定MIF和SIF运动神经元之间的超微结构差异。将用电子显微镜检查从内直肌逆行标记的两组样本，以确定它们的突触排列的差异是它们功能差异的基础。目的2检测cMRF是否与内、上级直肌MIF和SIF运动神经元及节前运动神经元接触。连接模式将提供有关cMRF动眼周投射是否与聚散度或共轭凝视有关，或者具有更广泛功能的见解。目的3将检验小脑顶核直接操纵负责近反应的运动神经元的假设。目的4测试顶盖投射到眼周区域是否是其共轭功能的一部分，垂直凝视运动神经元的树突是其目标，或者是调节近反应成分的通路。NEI的主要目标之一是治疗斜视和弱视，但我们在解决这些临床问题时遇到的最大困难之一是缺乏对其潜在机制的理解，特别是对控制透镜焦点或调节和维持适当眼睛对准的神经元回路的理解不足。本研究的目的是确定控制透镜和瞳孔的节前副交感神经运动神经元的运动前输入，以及控制眼外肌中多神经支配肌纤维（MIFs）的运动神经元，这可能对感知和调节眼睛的长期方向很重要。这些实验是第一个直接测试哪些大脑结构为这些运动神经元提供输入的实验。

Description (provided by applicant): This study investigates the circuitry of neurons in the perioculomotor region, which subserve the components of the near response and ocular orientation, and which may be important in the etiology of strabismus and amblyopia. The aims are directed at determining the premotor inputs to the preganglionic parasympathetic motor neurons that control the lens and pupil, and the motor neurons that control the multiply innervated muscle fibers (MIFs) in the extraocular muscles. MIFs are highly fatigue resistant and tonically active. They help adjust the pulley system, and are associated with palisade endings that may subserve ocular proprioception. Consequently, they may play a role in controlling normal eye orientation, and eye misalignment in strabismus. The preganglionic and MIF motor neuron groups are found in the perioculomotor region. This region also contains interneurons including those that utilize the neuropeptide urocortin, which is believed to play a role in stress behaviors. In order to define the circuitry that underlies the control of the lens, pupil and MIF fibers in the extraocular muscles, we must identify the premotor inputs to each. The proposed experiments will determine which of these elements is targeted by three of the known inputs to the perioculomotor region: the central mesencephalic reticular formation (cMRF), which may contain both saccade-related and vergence-related neurons, the fastigial nucleus, which is believed to modulate near triad responses in an adaptive manner, and the superior colliculus, which has a well known role in saccadic eye movements, but might play a role in the near response, as well. The proposal contains 4 inter-related neuroanatomical aims carried out in macaque monkeys. They feature experiments that combine anterograde tracers with either retrograde or immunohistochemical cell identification, and feature both LM and EM analysis. Aim 1 is directed at determining the ultrastructural differences between MIF and SIF motor neurons. Examples of the two groups, retrogradely labeled from the medial rectus muscle, will be examined with the electron microscope in order to determine what differences in their synaptic arrangements underlie their functional differences. Aim 2 will test whether the cMRF contacts medial and superior rectus MIF and SIF motor neurons and preganglionic motor neurons. The pattern of connections will provide insight into whether the cMRF perioculomotor projection is concerned with vergence or conjugate gaze, or has even wider functions. Aim 3 will test the hypothesis that the fastigial nucleus is directly manipulating the motoneurons responsible for the near response. Aim 4 tests whether the tectal projection to the perioculomotor region is part of its conjugate function, with the dendrites of vertical gaze motor neurons being its target, or is a pathway that modulates components of the near response. PUBLIC HEALTH RELEVANCE Work towards cures for strabismus and amblyopia are among the prime goals of the NEI, but one of the great difficulties we have in addressing these clinical problems is a lack of understanding of their underlying mechanisms, and specifically a poor understanding of the neuronal circuits that control lens focus or that adjust and maintain the proper eye alignment. The aims of this grant are directed at determining the premotor inputs to the preganglionic parasympathetic motor neurons that control the lens and pupil, and the motor neurons that control the multiply innervated muscle fibers (MIFs) in the extraocular muscles, which may be important for sensing and adjusting the long term orientation of the eyes. The proposed experiments are the first to directly test which brain structures supply input to these motor neurons.