Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger–Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.

中文翻译：

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小脑对猕猴中脑被盖的投射：可能的近响应连接

由于大多数视线转移是针对与当前目标距离观察者不同距离的目标，因此视线变化通常需要改变双眼之间的角度。作为此响应的一部分，还必须通过睫状肌根据目标距离调整晶状体曲率。有人提出，小脑顶峰和后部插入核对动眼神经上区 (SOA) 的投射支持这种行为，眼动上神经区紧靠动眼神经核背侧并包含近反应神经元。然而，SOA 还包含运动神经元，这些运动神经元提供多重神经支配的肌纤维 (MIF) 和提上睑肌运动神经元的树突。为了更好地确定 SOA 中顶核的目标，我们将顺行示踪剂放入这个小脑核中食蟹猴猴子和逆行示踪剂进入它们对侧的内直肌、上直肌和提睑肌。我们只观察到顺行标记的 boutons 与内直肌 MIF 和提睑肌运动神经元的树突之间的密切关联。然而，这些关联相对较少，表明这些不是主要的小脑目标。相反，在 SOA 和相邻的中央中脑网状结构 (cMRF) 中标记的 boutons 密集地支配神经元亚群。根据它们的位置，这些细胞可能代表运动前近反应神经元，它们供应内直肌和节前 Edinger-Westphal 运动神经元。我们还通过来自睫状肌的 N2c 狂犬病病毒的逆行跨突触转运，鉴定了与晶状体调节相关的小脑传入神经元。它们在顶峰和后部插入的核中双侧发现，其分布反映了从 SOA 和 cMRF 逆行标记的神经元的分布。我们的结果表明，这些小脑神经元通过靶向 cMRF 和 SOA 运动前神经元，在对称性聚散和分离性眼跳期间协调近响应的元素。