Underdeveloped extraocular muscles in the naked mole-rat (Heterocephalus glaber). 2010

Colleen A McMullen, and Francisco H Andrade, and Samuel D Crish
Departments of Physiology, University of Kentucky, Lexington, Kentucky, USA. cmcmu2@email.uky.edu

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.

UI MeSH Term Description Entries
D008810 Mice, Inbred C57BL One of the first INBRED MOUSE STRAINS to be sequenced. This strain is commonly used as genetic background for transgenic mouse models. Refractory to many tumors, this strain is also preferred model for studying role of genetic variations in development of diseases. Mice, C57BL,Mouse, C57BL,Mouse, Inbred C57BL,C57BL Mice,C57BL Mice, Inbred,C57BL Mouse,C57BL Mouse, Inbred,Inbred C57BL Mice,Inbred C57BL Mouse
D009210 Myofibrils The long cylindrical contractile organelles of STRIATED MUSCLE cells composed of ACTIN FILAMENTS; MYOSIN filaments; and other proteins organized in arrays of repeating units called SARCOMERES . Myofilaments,Myofibril,Myofilament
D009801 Oculomotor Muscles The muscles that move the eye. Included in this group are the medial rectus, lateral rectus, superior rectus, inferior rectus, inferior oblique, superior oblique, musculus orbitalis, and levator palpebrae superioris. Extraocular Muscles,Extraocular Rectus Muscles,Inferior Oblique Extraocular Muscle,Inferior Oblique Muscles,Levator Palpebrae Superioris,Musculus Orbitalis,Oblique Extraocular Muscles,Oblique Muscle, Inferior,Oblique Muscle, Superior,Oblique Muscles, Extraocular,Rectus Muscles, Extraocular,Superior Oblique Extraocular Muscle,Superior Oblique Muscle,Extraocular Muscle,Extraocular Muscle, Oblique,Extraocular Muscles, Oblique,Extraocular Oblique Muscle,Extraocular Oblique Muscles,Extraocular Rectus Muscle,Inferior Oblique Muscle,Muscle, Oculomotor,Muscles, Oculomotor,Oblique Extraocular Muscle,Oblique Muscle, Extraocular,Oblique Muscles, Inferior,Oblique Muscles, Superior,Oculomotor Muscle,Rectus Muscle, Extraocular,Superior Oblique Muscles
D009915 Orbit Bony cavity that holds the eyeball and its associated tissues and appendages. Eye Socket,Eye Sockets,Orbits,Socket, Eye,Sockets, Eye
D001766 Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of EYE DISEASES; OPTIC NERVE DISEASES; OPTIC CHIASM diseases; or BRAIN DISEASES affecting the VISUAL PATHWAYS or OCCIPITAL LOBE. Amaurosis,Bilateral Blindness,Blindness, Bilateral,Blindness, Legal,Blindness, Monocular,Blindness, Unilateral,Sudden Visual Loss,Unilateral Blindness,Blindness, Acquired,Blindness, Complete,Blindness, Hysterical,Blindness, Transient,Acquired Blindness,Amauroses,Bilateral Blindnesses,Complete Blindness,Hysterical Blindness,Legal Blindness,Monocular Blindness,Sudden Visual Losses,Transient Blindness,Visual Loss, Sudden
D005133 Eye Movements Voluntary or reflex-controlled movements of the eye. Eye Movement,Movement, Eye,Movements, Eye
D006243 Harderian Gland A sebaceous gland that, in some animals, acts as an accessory to the lacrimal gland. The harderian gland excretes fluid that facilitates movement of the third eyelid. Gland, Harderian
D000222 Adaptation, Physiological The non-genetic biological changes of an organism in response to challenges in its ENVIRONMENT. Adaptation, Physiologic,Adaptations, Physiologic,Adaptations, Physiological,Adaptive Plasticity,Phenotypic Plasticity,Physiological Adaptation,Physiologic Adaptation,Physiologic Adaptations,Physiological Adaptations,Plasticity, Adaptive,Plasticity, Phenotypic
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D001284 Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Atrophies

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