Human Extraocular Muscles Research Articles

The Immunoarchitecture of Human Extraocular Muscles.

The purpose of this study was to describe the immunoarchitecture of normal extraocular muscles (EOMs) in terms of presence, distribution, and organization of various immune cells. We performed unilateral orbital exenterations in six fresh human cadavers from elderly patients, followed by dissection of the medial, lateral, superior and inferior rectus, superior and inferior oblique, and superior palpebral levator muscle in their entirety. We further cross sectioned each EOM in an anterior, central, and posterior third. After immunohistochemical staining for CD3, CD8, CD20, CD138, CD68, and podoplanin, quantitative analysis was performed. We found all EOMs (rectus, oblique, and levator muscles) to harbor both T- and B-lymphocytes, with a B-lymphocyte dominance and an absence of plasma cells. The highest prevalence of immune cells was seen in the muscle bellies, with, on average, 488 ± 63 CD3+ T-lymphocytes and 44 ± 110 CD20+ B-lymphocytes per mm2, and significant differences from the anterior (T-lymphocytes) and posterior (T- and B-lymphocytes) thirds. T- and B-lymphocytes were primarily organized in hotspots in the vicinity of blood vessels. In addition, a small resident population of macrophages scattered throughout the specimens was detected. No lymphatic vessels were found in any of the EOMs. These findings can serve as a reference dataset in the assessment of EOM biopsies in the diagnostic process of inflammatory orbital and systemic disorders. Moreover, from a regenerative perspective, our results highlight the importance of taking into account the presence of a resident immune cell population when studying the host immune response on transplanted tissues or engineered constructs.

Quality assessment of polymer materials for human model eye development.

We developed model eyes using six polymer materials to determine which materials were most appropriate in simulating real human sclera and extraocular muscle (EOM). Five three-dimensional (3-D) printed polymers (FlexFill, PolyFlex, PCTPE, Soft PLA, and NinjaFlex) and one silicone material were systematically tested by board-certified ophthalmologists and senior ophthalmology residents. Material testing included scleral passes with 6-0 Vicryl sutures through each eye model. Participants completed a survey designed to collect demographic data, subjective assessment of each material's accuracy in simulating real human sclera and EOM, and a ranking for each polymer material to identify which would be most suitable for an ophthalmic surgery training tool. The Wilcoxon signed-rank test was conducted to determine if there was a statistically significant difference in the distribution of ranks between the polymer materials. The distribution of ranks for silicone material's "sclera" and "EOM" components were statistically significantly higher than that of all other polymer materials (all p < 0.05). Silicone material received the highest rank for both "sclera" and "EOM" components. Survey results indicated that the silicone material effectively simulated real human tissue. Silicone model eyes performed better than 3-D printed polymers as an educational tool for incorporation into a microsurgical training curriculum. Silicone models provide a low-cost teaching tool that allows for independent practice of microsurgical techniques without requiring a wet-laboratory facility.

Simulation of complex strabismus surgical procedures on goat eyes

To describe the possibility of complex strabismus surgical simulation on goat eyes. The goat eyes were procured from local slaughterhouse with retained extra ocular muscle tissues. The obtained eyes were inspected for globe integrity, muscle quality, muscle length, and the surrounding teno-conjunctival layers. The included eyes were then segregated for surgical simulation based on their insertion and orientation (as oblique or recti), and they were mounted on a mannequin head, with a fixation suture at free end to simulate the resting tension. Additionally, as per necessary, extra muscles were also transplanted along desired sites to simulate human extra ocular muscle anatomy. The inferior oblique, superior oblique, and all other four recti were successfully simulated in varying proportions in more than 50 eyes. Primarily, by simulating the lateral rectus, inferior rectus, and the inferior oblique muscle, staged weakening procedures of inferior oblique were successfully practiced (Fink's recession, Park's recession, Elliot and Nankin procedure, total anterior positioning, and antero-nasal trans-position or Stager's procedure). Similarly, by simulating superior rectus, inferior rectus, lateral rectus, and the medial rectus muscles, half width transposition, full width transposition, and other complex procedures were practiced (Knapp's procedure, augmented Knapp's, Nishida's procedure, Faden operation, and Y splitting procedure). Furthermore, by simulating superior oblique and the superior rectus muscles, superior oblique tuck, posterior tenectomy, loop tenotomy, and Harada Ito procedures were successfully practiced. On goat eyes, the complex strabismus surgical procedures can be successfully simulated and practiced after re-organizing the existing muscles in different patterns.

Neuroanatomical Structures in Extraocular Muscles and Their Potential Implication in the Management of Strabismus

Keywords: extraocular muscles, oculomotor anomalies, sensory receptors, strabismus Key points: • Human extraocular muscles contain neural structures important for the development and maintenance of binocular vision. • Strabismus and other oculomotor anomalies may be attributable to developmental delay or acquired dysfunctions associated with these structures. • Treatment options and their potential implications are discussed.

Cytoskeletal Proteins in Myotendinous Junctions of Human Extraocular Muscles.

PurposeThe purpose of this study was to investigate the cytoskeletal composition of myotendinous junctions (MTJs) in the human extraocular muscles (EOMs). Desmin and other major cytoskeletal proteins are enriched at the MTJs of ordinary myofibers, where they are proposed to be of particular importance for force transmission and required to maintain myofiber integrity.MethodsEOM and limb muscle samples were analyzed with immunohistochemistry using antibodies against the intermediate filament proteins desmin, nestin, keratin 19, vimentin, and different myosin heavy chain (MyHC) isoforms. MTJs were identified by labeling with antibodies against laminin or tenascin.ResultsIn contrast to MTJs in lumbrical muscle where desmin, nestin, and keratin 19 were always present, approximately one-third of the MTJs in the EOMs lacked either desmin and/or nestin, and all MTJs lacked keratin 19. Approximately 6% of the MTJs in the EOMs lacked all of these key cytoskeletal proteins.ConclusionsThe cytoskeletal protein composition of MTJs in human EOMs differed significantly from that of MTJs in limb muscles. These differences in cytoskeletal protein composition may indicate particular adaptation to meet the functional requirements of the EOMs.

Absence of Desmin in Myofibers of the Zebrafish Extraocular Muscles.

PurposeTo study the medial rectus (MR) muscle of zebrafish (Danio rerio) with respect to the pattern of distribution of desmin and its correlation to distinct types of myofibers and motor endplates.MethodsThe MRs of zebrafish were examined using confocal microscopy in whole-mount longitudinal specimens and in cross sections processed for immunohistochemistry with antibodies against desmin, myosin heavy chain isoforms, and innervation markers. Desmin patterns were correlated to major myofiber type and type of innervation. A total of 1382 myofibers in nine MR muscles were analyzed.ResultsFour distinct desmin immunolabeling patterns were found in the zebrafish MRs. Approximately a third of all slow myofibers lacked desmin, representing 8.5% of the total myofiber population. The adult zebrafish MR muscle displayed en grappe, en plaque, and multiterminal en plaque neuromuscular junctions (NMJs) with intricate patterns of desmin immunolabeling.ConclusionsThe MRs of zebrafish showed important similarities with the human extraocular muscles with regard to the pattern of desmin distribution and presence of the major types of NMJs and can be regarded as an adequate model to further study the role of desmin and the implications of heterogeneity in cytoskeletal protein composition.Translational RelevanceThe establishment of a zebrafish model to study the cytoskeleton in muscles that are particularly resistant to muscle disease opens new avenues to understand human myopathies and muscle dystrophies and may provide clues to new therapies.

Novel compact device for clinically measuring extraocular muscle (EOM) tension

Accurate knowledge of extraocular muscle (EOM) tension is important for the diagnosis of and surgical planning for strabismus, such as choosing which eye to operate or determining the amount of muscle displacement. Previous evaluations of passive EOM tension have relied extensively on the experience and skill of ophthalmic surgeons, who generally perform such evaluations by gripping the eyeball and then pushing and pulling it. This methodology, named the forced duction test, has the significant limitation that the tension is felt subjectively via the forceps, with the results therefore not being quantifiable. Previous quantitative analyses have utilized several different types of equipment with implanted force transducers or have involved connecting the muscle tendon to a strain gauge. However, the associated equipment setups and recording systems are highly complex and rarely used outside research settings. This situation prompted the present study to develop a novel compact, quantifiable and clinically applicable device for measuring the passive tension in human EOMs for use in clinical practice. The device employs locking forceps and a tilting sensor to rule out effects of the gripping force and to compensate for changes in the force due to tilting, which improves the measurement accuracy. The performance of the device was investigated in 60 eyes of 30 consecutive anaesthetized patients immediately prior to ophthalmic surgery. The results showed that the measured EOM tension in each rectus muscles agreed with previous findings: 48.3 ± 14.5 g (0.82 ± 0.28 g/deg, mean ± SD) for the lateral rectus, 45.6 ± 13.2 g (0.82 ± 0.23 g/deg) for the medial rectus, 48.6 ± 14.7 g (0.71 ± 0.21 g/deg) for the inferior rectus and 53.4 ± 13.7 g (0.77 ± 0.25 g/deg) for the superior rectus.

Complex Correlations Between Desmin Content, Myofiber Types, and Innervation Patterns in the Human Extraocular Muscles.

PurposeTo investigate whether the distribution of intermediate filament protein desmin is related to the different patterns of innervation in the human extraocular muscles (EOMs).MethodsEOM samples were analyzed with immunohistochemistry using antibodies against desmin, vimentin, different myosin heavy chain (MyHC) isoforms, and fetal and adult acetylcholine receptor (AChR) subunits. Neuromuscular junctions (NMJs) were identified with α-bungarotoxin or with antibodies against neurofilament and synaptophysin.ResultsDesmin was present in the vast majority of myofibers, but it was weakly present or absent in a limited area in the close vicinity of the single en plaque NMJs in less than half of these myofibers. Desmin was either present or lacking in MyHCsto/I myofibers displaying multiple en grappe endings but present in MyHCsto/I myofibers receiving spiral nerve endings. In MyHCeom myofibers displaying multiterminal en plaque endings, desmin was either present or absent irrespective of AChR subunits or EOM layer. Vimentin did not substitute for the lack of desmin.ConclusionsThe results indicate that the human EOMs have a more complex cytoskeletal organization than other muscles and suggest additional signalling mechanisms from the NMJs to the myofibers.

Comparison of lateral and medial rectus muscle in human: an anatomical study with particular emphasis on morphology, intramuscular innervation pattern variations and discussion on clinical significance

This paper aims to present various aspects of the anatomy of horizontal (i.e., lateral and medial) rectus muscles. It mainly compares morphology and detailed patterns of intramuscular innervation of those muscles. It is also one of the first reports that uses the Sihler's stain to examine human extraocular muscles. The study was conducted on 80 isolated cadaveric hemi-heads. Sihler technique of nerves staining served to expose the course of intramuscular branches of the oculomotor and abducens nerves. The lateral rectus was longer (48mm versus 46.5mm) and more distant from the limbus (6.8mm versus 5.7mm) than the medial rectus muscle. Three variants of the abducens nerve primary division were observed in the lateral rectus muscle. In the medial rectus muscle, the motor branch from the oculomotor nerve was more evenly divided into sub-branches. In both examined horizontal rectus muscles, primary muscular branches split into secondary sub-branches, which undergo numerous further divisions. The most numerous terminal sub-branches formed the terminal plexus. The distance between the insertion and the anterior-most end of the terminal plexus referenced to the total length of the muscle ranged from 35.4 to 48.5% for the lateral rectus muscle and from 36.3 to 50.5% for medial rectus muscle. Both horizontal rectus muscles share similar general pattern of distribution of intramuscular nerves, with characteristic root-like arborizations of sub-branches. The terminal nerve plexus was observed near half of both muscles' length. Knowledge of variations and innervation pattern of the extraocular muscles may be relevant during ophthalmology surgeries.

An accurate interactive segmentation and volume calculation of orbital soft tissue for orbital reconstruction after enucleation

BackgroundAccurate measurement and reconstruction of orbital soft tissue is important to diagnosis and treatment of orbital diseases. This study applied an interactive graph cut method to orbital soft tissue precise segmentation and calculation in computerized tomography (CT) images, and to estimate its application in orbital reconstruction.MethodsThe interactive graph cut method was introduced to segment extraocular muscle and intraorbital fat in CT images. Intra- and inter-observer variability of tissue volume measured by graph cut segmentation was validated. Accuracy and reliability of the method was accessed by comparing with manual delineation and commercial medical image software. Intraorbital structure of 10 patients after enucleation surgery was reconstructed based on graph cut segmentation and soft tissue volume were compared within two different surgical techniques.ResultsBoth muscle and fat tissue segmentation results of graph cut method showed good consistency with ground truth in phantom data. There were no significant differences in muscle calculations between observers or segmental methods (p > 0.05). Graph cut results of fat tissue had coincidental variable trend with ground truth which could identify 0.1cm3 variation. The mean performance time of graph cut segmentation was significantly shorter than manual delineation and commercial software (p < 0.001). Jaccard similarity and Dice coefficient of graph cut method were 0.767 ± 0.045 and 0.836 ± 0.032 for human normal extraocular muscle segmentation. The measurements of fat tissue were significantly better in graph cut than those in commercial software (p < 0.05). Orbital soft tissue volume was decreased in post-enucleation orbit than that in normal orbit (p < 0.05).ConclusionThe graph cut method was validated to have good accuracy, reliability and efficiency in orbit soft tissue segmentation. It could discern minor volume changes of soft tissue. The interactive segmenting technique would be a valuable tool for dynamic analysis and prediction of therapeutic effect and orbital reconstruction.

Extraocular muscle function is impaired in ryr3 -/- mice.

Calcium is an ubiquitous second messenger mediating numerous physiological processes, including muscle contraction and neuronal excitability. Ca2+ is stored in the ER/SR and is released into the cytoplasm via the opening of intracellular inositol trisphosphate receptor and ryanodine receptor calcium channels. Whereas in skeletal muscle, isoform 1 of the RYR is the main channel mediating calcium release from the SR leading to muscle contraction, the function of ubiquitously expressed ryanodine receptor 3 (RYR3) is far from clear; it is not known whether RYR3 plays a role in excitation-contraction coupling. We recently reported that human extraocular muscles express high levels of RYR3, suggesting that such muscles may be useful to study the function of this isoform of the Ca2+ channel. In the present investigation, we characterize the visual function of ryr3-/- mice. We observe that ablation of RYR3 affects both mechanical properties and calcium homeostasis in extraocular muscles. These changes significantly impact vision. Our results reveal for the first time an important role for RYR3 in extraocular muscle function.

Functional anatomy of extraocular muscles during human vergence compensation of horizontal heterophoria

We employed magnetic resonance imaging to quantify human extraocular muscle (EOM) contractility during intermittent convergent and divergent strabismus with each eye viewing monocularly at 20 cm compared with centered target fusion. Contractility, indicated by posterior partial volume change, was analyzed in transverse rectus and in medial and lateral superior oblique (SO) muscle compartments. In five subjects with intermittent esotropia, abduction of the deviated eye to monocular target fixation was associated with significant whole lateral rectus (LR) contraction, but with medial rectus (MR) relaxation that was significantly greater in the superior than inferior compartment. Esotropic eye abduction to binocular fusion was associated with similar relaxation in the two MR compartments, but with greater contraction in the LR's superior than inferior compartment. The whole diverging eye SO muscle relaxed. In three subjects with intermittent exotropia, converging eye fusional adduction was associated with significant whole LR relaxation and with MR contraction attributable to significantly greater contraction in the superior than inferior compartment. In adduction of the exotropic eye to monocular target fixation but not fusional adduction, the whole SO exhibited significant relaxation. Rectus pulley positions were not significantly altered by fusion of either form of intermittent strabismus. Globe rotational axis was eccentric in intermittent strabismus, rolling the eye so that rectus EOM lever arms facilitated vergence. These results confirm, and extend to fusion of intermittent horizontal strabismus, differential compartmental function in horizontal rectus EOMs and suggest a novel role for the SO in compensation of both intermittent esotropia and exotropia. NEW & NOTEWORTHY Disjunctive eye movements normally permit binocular fixation in near visual space but also compensate for mechanical imbalances in binocular alignment developing over the life span. Magnetic resonance imaging of the extraocular muscles demonstrates important differential function in muscle compartments during compensation of large-angle intermittent convergent and divergent strabismus in humans. Eye translation during rotation also enhances vergence compensation of intermittent strabismus.

Isolation of Multipotent Mesenchymal Stem Cells from Human Extraocular Muscle Tissue.

Mesenchymal stem cells (MSCs) have attracted significant attention as potential therapeutic cells to treat various diseases ranging from tissue injuries, graft versus host disease, degenerative diseases and cancer. Since the initial discovery of MSCs in the bone marrow cells, MSCs have been successfully isolated from various adult and neo-natal tissues, albeit the procedures are often coupled with difficulties in harvesting tissue and produce low yield of cells, requiring extensive expansion in vitro. Here, we explored extra-ocular muscle tissues obtained from patients as a novel source of MSCs which express characteristic cell surface markers of MSCs and show multilineage differentiation potential with high proliferation capacity.

Functional anatomy of human extraocular muscles during fusional divergence.

We employed magnetic resonance imaging to quantify human extraocular muscle contractility during centered target fusion and fusional divergence repeated with each eye viewing monocularly at 20 cm through 8Δ and at 400 cm through 4Δ base in prism. Contractility, indicated by posterior partial volume (PPV) change, was analyzed in transverse rectus and in medial and lateral superior oblique (SO) muscle compartments and by cross-sectional area change in the inferior oblique (IO). At 20 cm, 3.1 ± 0.5° (SE) diverging eye abduction in 10 subjects was associated with 4.2 ± 1.5% whole lateral rectus (LR) PPV increase ( P < 0.05) and 1.7 ± 1.1% overall medial rectus (MR) PPV decrease attributable to 3.1 ± 1.8% reduction in the superior compartment ( P < 0.025), without change in its inferior compartment or in muscles of the aligned eye. At 400 cm, 2.2 ± 0.5° diverging eye abduction in nine subjects was associated with 6.1 ± 1.3% whole LR PPV increase ( P < 10-5) but no change in MR, with compartmentally similar relaxation in the LR and MR of the aligned eye. Unlike convergence, there were no IO or SO contractile changes for divergence to either target nor any change in rectus pulley positions. Results confirm and extend to proximal divergence the unique role of the superior MR compartment, yet no MR role for far divergence. Corelaxation of aligned eye LR and MR combined with failure of MR relaxation during divergence is consistent with the limited behavioral range of divergence. NEW & NOTEWORTHY Magnetic resonance imaging shows that the lateral rectus muscle must overcome continued contraction by its opponent the medial rectus when humans diverge their visual axes to achieve single, binocular vision. While the upper but not lower compartment of the medial rectus assists by relaxing for near targets, it does not do so when targets are far away. This behavior violates Sherrington's law of reciprocal action of antagonists and conventional assumptions about the ocular motor system.

Thyroid-Stimulating Hormone Receptor Expression on Primary Cultured Human Extraocular Muscle Myoblasts

ABSTRACT Purpose To isolate and culture human extraocular muscle (EOM) myoblasts and facilitate their differentiation to myotubes in vitro, and to determine whether these myoblasts express thyroid-stimulating hormone receptor (TSHR). Materials and methods Human EOM myoblasts were isolated from EOM samples, and identified by immunostaining for PAX7 and MYOD1 (markers of human skeletal myoblasts), and western blot for desmin (muscle marker). In addition, we investigated the expressions of SHOX2 (a genetic marker of EOM myoblasts) and HOXC10 (an exclusive marker of hind-limb muscle-derived myoblasts) by RT-PCR. Fusion index and myotube area were measured to quantify myotube differentiation. TSHR immunostaining and western blot were used to determine the presence of TSHR on human EOM myoblasts and investigate its expression during myogenesis. Results Human EOM myoblasts were immunopositive for PAX7 and MYOD1 staining, and had desmin expression during myogenesis. The EOM-specific gene SHOX2 was detected by RT-PCR, but HOXC10 was not detected. The significant change in both fusion index and myotubes were shown at 8 days after induction of differentiation myotubes. Immunostaining revealed TSHR was expressed on human EOM myoblasts and western blot demonstrated the presence of TSHR protein and highest TSHR protein expression was shown at 10 days after myogenic differentiation. Conclusions Human EOM myoblasts were cultured and underwent myogenic differentiation in vitro. TSHR protein was detected on human EOM myoblasts and increasing TSHR expression during myogenic differentiation.

A Novel Type of Multiterminal Motor Endplate in Human Extraocular Muscles.

To investigate the relation between type of motor endplate, acetylcholine receptor (AChR) subunit composition, and fiber types in human extraocular muscles (EOMs). EOM samples collected from subjects aged 34 to 82 years were serially sectioned and processed for immunohistochemistry, with specific antibodies against different myosin heavy chain (MyHC) isoforms, neurofilament, synaptophysin, and adult epsilon (ε) and fetal gamma (γ) AChR subunits as well as α-bungarotoxin. A novel type of motor endplate consisting of large, multiterminal en plaque endings was found in human EOMs, in addition to the previously well-described single en plaque and multiple en grappe endplates. Such novel endplates were abundant but exclusively observed in myofibers lacking MyHC slow and fast IIa but containing MyHC extraocular (MyHCeom), isoforms. Multiple en grappe endings were found only in myofibers containing MyHC slow-tonic isoform and contained fetal γ AChR subunit. Adult ε and fetal γ AChR subunits, alone or combined, were found in the multiterminal endplates. Distinct AChR subunits were present in adjacent motor endplates of a given myofiber containing MyHCeom. Human EOMs have a more complex innervation pattern than previously described, comprising also a novel type of multiterminal motor endplate present in myofibers containing MyHCeom. The heterogeneity in AChR subunit composition in a given myofiber suggests the possible presence of polyneuronal innervation in human EOMs.

Neuroanatomical Structures in Human Extraocular Muscles and Their Potential Implication in the Development of Oculomotor Disorders.

The potential role of sensory feedback from human extraocular muscles has been subjected to considerable speculation in the ophthalmic literature. Extraocular muscles pull against a fairly even load and do not initiate a stretch reflex, even when the eyes are directed toward the boundaries of their respective field of action. These unique working conditions and physiological properties have led to the notion that the sensory signal arising from receptors in extraocular muscles differs from the conventional proprioceptive signal arising from their somatic counterparts. The interest in the receptors at the myotendinous junction of human extraocular muscles has been renewed due to their alleged role in the development of binocular vision and their potential implication in the etiology of binocular vision anomalies. The idea that extraocular muscles provide knowledge of eye position and whether this function can be affected by surgical intervention has initiated several clinical and neuroanatomical studies. Many of these studies support this concept and suggest that surgical procedures that impose only minimal interference with the proprioceptive signal will give a better postoperative result. However, other studies contradict this view because the afferent capacity of the receptors can be questioned and some uncertainties remain. The purpose of this study was to review the related literature and discuss the possible role of ocular proprioceptors in relation to binocular vision and the development of eye motility disorders. [J Pediatr Ophthalmol Strabismus. 2018;55(1):14-22.].

Extraocular Muscle Repair and Regeneration.

The goal of this review is to summarize the unique regenerative milieu within mature mammalian extraocular muscles (EOMs). This will aid in understanding disease propensity for and sparing of EOMs in skeletal muscle diseases as well as the recalcitrance of the EOM to injury. The EOMs continually remodel throughout life and contain an extremely enriched number of myogenic precursor cells that differ in number and functional characteristics from those in limb skeletal muscle. The EOMs also contain a large population of Pitx2-positive myogenic precursor cells that provide the EOMs with many of their unusual biological characteristics, such as myofiber remodeling and skeletal muscle disease sparing. This environment provides for rapid and efficient remodeling and regeneration after various types of injury. In addition, the EOMs show a remarkable ability to respond to perturbations of single muscles with coordinated changes in the other EOMs that move in the same plane. These data will inform Ophthalmologists as they work toward developing new treatments for eye movement disorders, new approaches for repair after nerve or direct EOMs injury, as well as suggest potential explanations for the unusual disease propensity and disease sparing characteristics of human EOM.

Biochemical and Mechanical Properties of Murine Extraocular Muscles

Extraocular muscles (EOMs) are among the fastest and most fatigue resistant skeletal muscles. The distinct origin and innervation of EOMs are probably responsible for their different gene and protein expression. Indeed, western blot analysis revealed that the expression of the protein isoforms forming the Excitation-Contraction Coupling Macromolecular Complex (ECC-MC) of human EOM is substantially different from human quadriceps muscles. Human EOM muscles express, in addition to the skeletal muscle isoforms of proteins involved in ECC, Cav1.2, CASQ2 and RYR3. Because of the use of genetically modified mouse models to study human diseases we thought it important to investigate the biochemical and mechanical properties of murine EOM. We found that the expression level of the ECC-MC proteins in mouse EOM is different from that of mouse hind limb muscles and from that of human EOM. We also studied the mechanical properties of mouse EOM. In the presence of 1.8 mM CaCl2 in the extracellular medium the force induced by a single action potential and by a train of action potentials delivered at 100 Hz was 40,4±35,7 µN (n=8), 359±213 µN (n=8 ), respectively . The half time to peak, the time to peak and the half relaxation times of force development evoked by a single action potential were 2.53±0.69 ms (n=8), 10.1±0.3 ms (n=8), 42.3±27.8 ms (n= 8), respectively. Addition of 100 µM La3+ to the extrcellular medium caused a mean decrease of 75 % of the peak tetanic tension. The effect of La3+ was reversed by washing the muscle with Tyrode's solution containing 1.8 mM CaCl2 This study defines the biochemical and mechanical properties of preparations of mouse EOM under normal conditions and will be used as reference to investigate the phenotype of EOM from mice carrying modifications of genes encoding key proteins encompassing the ECC-MC.

Impact of Amyotrophic Lateral Sclerosis on Slow Tonic Myofiber Composition in Human Extraocular Muscles.

To analyze the proportion and cross-sectional area of myofibers containing myosin heavy chain slow-twitch (MyHCI) and myosin heavy chain slow tonic (MyHCsto) in extraocular muscles of autopsied amyotrophic lateral sclerosis (ALS) patients with either spinal or bulbar site of disease onset. Whole-muscle cross sections from the middle portion of the medial rectus were labeled with antibodies against MyHCI or MyHCsto and laminin. Myofibers labeled with the MyHC antibodies (MyHCI+sto) and the total number of myofibers were quantified in the orbital and global layer of 6 control individuals and 18 ALS patients. The cross-sectional area of myofibers labeled for either MyHC was quantified in 130 to 472 fibers/individual in the orbital and in 180 to 573 fibers/individual in the global layer of each specimen. The proportion of MyHCI+sto myofibers was significantly smaller in the orbital and global layer of ALS compared to control individuals. MyHCI+sto myofibers were significantly smaller in the global layer than in the orbital layer of ALS, whereas they were of similar size in control subjects. The decreased proportion of MyHCI+sto fibers correlated significantly with the age of death, but not disease duration, in patients who had the bulbar-onset variant of ALS but not in patients with spinal variant. ALS, regardless of site of onset, involves a loss of myofibers containing MyHCI+sto. Only in bulbar-onset cases did aging seem to play a role in the pathophysiological processes underlying the loss of MyHCI+sto fibers.