Graf W, Brunken W J
J Comp Neurol. 1984 Aug 20;227(4):569-81. doi: 10.1002/cne.902270408.
The oculomotor organization of two elasmobranch species, smooth dogfish (Mustelus canis) and little skate (Raja erinacea), was studied by investigating the extraocular muscle apparatus and the oculomotor motoneuron distribution. The macroscopic appearance of the eye muscles was similar to any lateral-eyed vertebrate species (e.g., goldfish, rabbit). The size of extraocular muscles was expressed by counting single muscle fibers and comparing cross-sectional areas of the extraocular muscles. There were significant differences in the number of fibers in the six extraocular muscles in dogfish, but not in skate. Fiber sizes varied considerably; thus, the number of fibers did not relate to cross-sectional areas. In the dogfish, no one pair of agonist-antagonist extraocular muscles was larger than the others, suggesting that there was no preference for eye movements in a particular plane of space. However, the lateral rectus was more than twice the size of most of the other muscles. In the skate, cross-sectional areas of the horizontal eye muscles were smaller than those of the vertical eye movers. This may indicate a reduced utilization of horizontal eye muscles, which may reflect the bottom-dwelling habitat and mode of locomotion of the skate. The distribution of the extraocular motoneurons was determined by injecting horseradish peroxidase (HRP) into single eye muscles. Medial rectus, superior rectus, and superior oblique motoneuron populations were located contralateral to their respective muscles. Lateral rectus, inferior rectus, and inferior oblique motoneurons were located ipsilateral to their muscles. This distribution is in contrast to almost all other vertebrates studied thus far, where medial rectus motoneurons are located ipsilateral to the muscle which they innervate. The oculomotor arrangement in elasmobranchs is likely to have consequences for the circuitry responsible for the production of conjugate compensatory eye movements in the horizontal plane. We hypothesize that, in contrast to other vertebrates, the basic elasmobranch vestibulo-ocular reflex pathway consists of three identically structured three-neuron-arcs connecting the three semicircular canals to their respective extraocular muscles. This innervation pattern may constitute a special feature of the elasmobranch brain or a phylogenetically older arrangement of eye movement pathways.
通过研究眼外肌装置和动眼运动神经元分布，对两种板鳃亚纲鱼类——平滑狗鲨（Mustelus canis）和小鳐（Raja erinacea）的动眼组织进行了研究。眼肌的宏观外观与任何侧眼脊椎动物物种（如金鱼、兔子）相似。通过计数单根肌纤维并比较眼外肌的横截面积来表示眼外肌的大小。狗鲨的六条眼外肌中的纤维数量存在显著差异，但鳐鱼中没有。纤维大小差异很大；因此，纤维数量与横截面积无关。在狗鲨中，没有一对拮抗肌眼外肌比其他肌更大，这表明在特定空间平面上对眼球运动没有偏好。然而，外直肌的大小是大多数其他肌肉的两倍多。在鳐鱼中，水平眼肌的横截面积小于垂直眼肌的横截面积。这可能表明水平眼肌的利用率降低，这可能反映了鳐鱼的底栖栖息地和运动方式。通过将辣根过氧化物酶（HRP）注入单条眼肌来确定眼外运动神经元的分布。内直肌、上直肌和上斜肌运动神经元群体位于与其各自肌肉相对的一侧。外直肌、下直肌和下斜肌运动神经元位于与其肌肉同侧。这种分布与迄今为止研究的几乎所有其他脊椎动物相反，在其他脊椎动物中，内直肌运动神经元位于它们所支配肌肉的同侧。板鳃亚纲动物的动眼排列可能会对负责在水平面产生共轭补偿性眼球运动的神经回路产生影响。我们假设，与其他脊椎动物不同，基本的板鳃亚纲前庭眼反射通路由三个结构相同的三神经元弧组成，将三个半规管连接到它们各自的眼外肌。这种神经支配模式可能构成板鳃亚纲动物大脑的一个特殊特征，或者是眼球运动通路在系统发育上更古老的排列方式。
