Departments of Physiology, University of Kentucky, Lexington, Kentucky, USA.
Anat Rec (Hoboken). 2010 May;293(5):918-23. doi: 10.1002/ar.21107.
The extraocular muscles (EOM), the effector arm of the ocular motor system, have a unique embryological origin and phenotype. The naked mole-rat (NMR) is a subterranean rodent with an underdeveloped visual system. It has not been established if their ocular motor system is also less developed. The NMR is an ideal model to examine the potential codependence of oculomotor and visual system development and evolution. Our goal was to compare the structural features of NMR EOMs to those of the mouse, a similar sized rodent with a fully developed visual system. Perfusion-fixed whole orbits and EOMs were dissected from adult NMR and C57BL mice and examined by light and electron microscopy. NMR orbital anatomy showed smaller EOMs in roughly the same distribution around the eye as in mouse and surrounded by a very small Harderian gland. The NMR EOMs did not appear to have the two-layer fiber distribution seen in mouse EOMs; fibers were also significantly smaller (112.3 +/- 46.2 vs. 550.7 +/- 226 sq microm in mouse EOMs, *P < 0.05). Myofibrillar density was less in NMR EOMs, and triad and other membranous structures were rudimentary. Finally, mitochondrial volume density was significantly less in NMR EOMs than in mouse EOM (4.5% +/- 1.9 vs. 21.2% +/- 11.6, respectively, *P < 0.05). These results demonstrate that NMR EOMs are smaller and less organized than those in the mouse. The "simpler" EOM organization and structure in NMR may be explained by the poor visual ability of these rodents, initially demonstrated by their primitive visual system.
眼外肌（EOM）是眼球运动系统的效应器臂，具有独特的胚胎起源和表型。裸鼹鼠（NMR）是一种地下啮齿动物，视觉系统发育不全。尚未确定它们的眼动系统是否也发育不全。NMR 是研究眼动系统和视觉系统发育和进化潜在依赖性的理想模型。我们的目标是比较 NMR EOM 的结构特征与具有完全发育的视觉系统的类似大小的啮齿动物小鼠的结构特征。从成年 NMR 和 C57BL 小鼠中分离出灌注固定的整个眼眶和 EOM，并通过光镜和电子显微镜进行检查。NMR 眼眶解剖显示，EOM 的大小大致相同，分布在小鼠的眼睛周围，周围是非常小的哈氏腺。NMR EOM 似乎没有在小鼠 EOM 中看到的两层纤维分布；纤维也明显较小（NMR EOM 为 112.3 +/- 46.2μm，小鼠 EOM 为 550.7 +/- 226μm，*P < 0.05）。NMR EOM 的肌原纤维密度较低，三联体和其他膜结构也很原始。最后，NMR EOM 中的线粒体体积密度明显低于小鼠 EOM（分别为 4.5% +/- 1.9%和 21.2% +/- 11.6%，*P < 0.05）。这些结果表明，NMR EOM 比小鼠的 EOM 更小且组织化程度更低。NMR 中 EOM 组织和结构的“简单性”可能是由于这些啮齿动物的视觉能力较差，最初表现在它们原始的视觉系统上。
