Center of Anatomy and Cell Biology, Integrative Morphology Group, Medical University Vienna, A-1090 Vienna, Austria.
J Neurosci. 2013 Feb 13;33(7):2784-93. doi: 10.1523/JNEUROSCI.4116-12.2013.
Palisade endings are nerve specializations found in the extraocular muscles (EOMs) of mammals, including primates. They have long been postulated to be proprioceptors. It was recently demonstrated that palisade endings are cholinergic and that in monkeys they originate from the EOM motor nuclei. Nevertheless, there is considerable difference of opinion concerning the nature of palisade ending function. Palisade endings in EOMs were examined in cats to test whether they display motor or sensory characteristics. We injected an anterograde tracer into the oculomotor or abducens nuclei and combined tracer visualization with immunohistochemistry and α-bungarotoxin staining. Employing immunohistochemistry, we performed molecular analyses of palisade endings and trigeminal ganglia to determine whether cat palisade endings are a cholinergic trigeminal projection. We confirmed that palisade endings are cholinergic and showed, for the first time, that they, like extraocular motoneurons, are also immunoreactive for calcitonin gene-related peptide. Following tracer injection into the EOM nuclei, we observed tracer-positive palisade endings that exhibited choline acetyl transferase immunoreactivity. The tracer-positive nerve fibers supplying palisade endings also established motor terminals along the muscle fibers, as demonstrated by α-bungarotoxin. Neither the trigeminal ganglion nor the ophthalmic branch of the trigeminal nerve contained cholinergic elements. This study confirms that palisade endings originate in the EOM motor nuclei and further indicates that they are extensions of the axons supplying the muscle fiber related to the palisade. The present work excludes the possibility that they receive cholinergic trigeminal projections. These findings call into doubt the proposed proprioceptive function of palisade endings.
边缘终末是哺乳动物（包括灵长类动物）眼外肌（EOM）中的神经特化结构，长期以来被认为是本体感受器。最近的研究表明，边缘终末是胆碱能的，在猴子中，它们起源于 EOM 运动核。然而，关于边缘终末功能的性质存在相当大的意见分歧。本研究在猫中检查了 EOM 中的边缘终末，以测试它们是否具有运动或感觉特征。我们将顺行示踪剂注入动眼神经或展神经核，并将示踪可视化与免疫组织化学和α-银环蛇毒素染色相结合。我们通过免疫组织化学对边缘终末和三叉神经节进行了分子分析，以确定猫的边缘终末是否是胆碱能三叉神经投射。我们证实边缘终末是胆碱能的，并首次表明，它们与眼外 motoneurons 一样，也对降钙素基因相关肽呈免疫反应。在 EOM 核内注射示踪剂后，我们观察到示踪阳性的边缘终末，其表现出胆碱乙酰转移酶免疫反应性。示踪阳性的供应边缘终末的神经纤维也在肌肉纤维上建立了运动终末，如α-银环蛇毒素所证明的那样。三叉神经节和三叉神经的眼支都不含有胆碱能成分。这项研究证实边缘终末起源于 EOM 运动核，并进一步表明它们是供应与边缘相关的肌纤维的轴突的延伸。目前的工作排除了它们接收胆碱能三叉神经投射的可能性。这些发现质疑了边缘终末的拟本体感受功能的假说。
