Mouse Extraocular Muscles and the Musculotopic Organization of Their Innervation

Abstract

The organization of extraocular muscles (EOMs) and their motor nuclei was investigated in the mouse due to the increased importance of this model for oculomotor research. Mice showed a standard EOM organization pattern, although their eyes are set at the side of the head. They do have more prominent oblique muscles, whose insertion points differ from those of frontal‐eyed species. Retrograde tracers revealed that the motoneuron layout aligns with the general vertebrate plan with respect to nuclei and laterality. The mouse departed in some significant respects from previously studied species. First, more overlap between the distributions of muscle‐specific motoneuronal pools was present in the oculomotor nucleus (III). Furthermore, motoneuron dendrites for each pool filled the entire III and extended beyond the edge of the abducens nucleus (VI). This suggests mouse extraocular motoneuron afferents must target specific pools based on features other than dendritic distribution and nuclear borders. Second, abducens internuclear neurons are located outside the VI. We concluded this because no unlabeled abducens internuclear neurons were observed following lateral rectus muscle injections and because retrograde tracer injections into the III labeled cells immediately ventral and ventrolateral to the VI, not within it. This may provide an anatomical substrate for differential input to motoneurons and internuclear neurons that allows rodents to move their eyes more independently. Finally, while soma size measurements suggested motoneuron subpopulations supplying multiply and singly innervated muscle fibers are present, markers for neurofilaments and perineuronal nets indicated overlap in the size distributions of the two populations. Anat Rec, 302:1865–1885, 2019. © 2019 American Association for Anatomy

Intramuscular innervation of the lateral rectus muscle evaluated using sihler's staining technique: Potential application to strabismus surgery

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Transduction of Craniofacial Motoneurons Following Intramuscular Injections of Canine Adenovirus Type-2 (CAV-2) in Rhesus Macaques

“…Crosstalk of viruses between the muscles would be noticeable via unexpected labeling in the cranial nuclei. The motoneurons innervating each extraocular muscle reside either in a separate nucleus or, on average, in relatively segregated pools within the same nucleus: lateral rectus motoneurons reside in the abducens nucleus (VI), superior oblique motoneurons reside in the trochlear nucleus (IV), and motoneurons innervating the remaining four extraocular muscles and the levator reside in clustered pools within the oculomotor nucleus (III) with the medial rectus, inferior rectus and inferior oblique motoneurons sitting in pools within the oculomotor nucleus ipsilateral to the muscle they innervate, while the superior rectus motoneurons sit within the contralateral oculomotor nucleus to the orbit the innervate (Evinger, 1988; Büttner-Ennever et al, 2001; Bohlen et al, 2017b, 2019). The instance where this was an issue in the present study was the distinction between CAV-2-hChAT-GFP which was injected into the inferior rectus and CAV-2-CMV-mCitrine which was injected into the superior rectus.…”

Distribution and postnatal development of chondroitin sulfate proteoglycans in the perineuronal nets of cholinergic motoneurons innervating extraocular muscles

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