MIDBRAIN CIRCUITRY FOR NEURONAL CONTROL OF GAZE

描述(申请人提供)：这项研究调查了动眼周围区域神经元的回路，它伴随着近视反应和眼球方向的成分，这在斜视和弱视的病因中可能是重要的。其目的是确定控制晶状体和瞳孔的节前副交感运动神经元的运动前输入，以及控制眼外肌中多神经支配的肌肉纤维(MIF)的运动神经元。MIF具有高度的抗疲劳性和调理活性。它们有助于调整滑轮系统，并与栅栏末端相关，可能有助于眼睛本体感觉。因此，它们可能在控制正常的眼球朝向和斜视时的眼球错位方面发挥作用。节前运动神经元组和MIF运动神经元组位于动眼周围区。这一区域还包含中间神经元，包括那些利用神经肽urocortin的神经元，该神经肽被认为在应激行为中发挥作用。为了确定控制晶状体、瞳孔和眼外肌中MIF纤维的电路，我们必须识别每一个的运动前输入。拟议的实验将确定这些元素中的哪些是三个已知输入到动眼周围区域的靶点：中央中脑网状结构(CMRF)，它可能包含眼跳相关和聚集相关的神经元；顶核，据信以一种适应性的方式调制近三联反应；上丘，它在扫视眼球运动中具有众所周知的作用，但也可能在近距离反应中发挥作用。该提案包含了在猕猴身上实现的4个相互关联的神经解剖学目标。它们的特点是将顺行示踪剂与逆行或免疫组织化学细胞鉴定相结合的实验，并同时进行光镜和EM分析。目的1旨在确定MIF和SIF运动神经元的超微结构差异。从内直肌逆行标记的两组样本将用电子显微镜进行检查，以确定它们在突触排列上的差异是什么导致了它们的功能差异。目的2测试cMRF是否与内侧和上直肌MIF和SIF运动神经元以及节前运动神经元接触。这种联系模式将提供关于cmrf眼周运动投射是否与聚焦或共轭凝视有关的洞察，或者具有更广泛的功能。目标3将验证顶核直接操纵负责近距离反应的运动神经元的假设。目的4测试以垂直凝视运动神经元树突为靶点的顶盖至动眼周围区的投射是其共轭功能的一部分，还是调节近距离反应成分的通路。与公共卫生相关的治疗斜视和弱视的工作是NEI的主要目标之一，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了解，特别是对控制晶状体焦点或调整和保持适当眼球对齐的神经回路缺乏了解。这笔赠款的目的是确定控制晶状体和瞳孔的节前副交感运动神经元的运动前输入，以及控制眼外肌中多神经支配的肌肉纤维(MIF)的运动神经元，这可能对感知和调整眼睛的长期方向很重要。拟议中的实验是第一次直接测试哪些大脑结构为这些运动神经元提供输入。

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.