Extraocular Motor Unit and Whole-Muscle Responses in the Lateral Rectus Muscle of the Squirrel Monkey

Goldberg, Stephen J.; Meredith, M. Alex; Shall, Mary S.

doi:10.1523/jneurosci.18-24-10629.1998

Cited by 62 publications

(68 citation statements)

References 45 publications

(92 reference statements)

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“…The maximum tetanic tension was seen at or near the fusion frequency of the muscle. Fusion frequency was defined as the stimulation frequency at which individual twitches could not be differentiated at the tension plateau (Goldberg et al, 1998). Fatigability was measured by a stimulation of 5 second duration at fusion frequency (Asmussen, 1978;Stelling and McVean, 1988).…”

Section: Stimulation Parametersmentioning

confidence: 99%

“…Fusion frequency for control animals was usually between 300 -400 Hz. Fusion frequency is the stimulation frequency at which individual twitches could not be differentiated at the tension plateau (Goldberg et al, 1998). Maximum tetanic tension was reached at or close to the fusion frequency and further increases of the rate of stimulation did not lead to an increase in the developed tension.…”

Section: Contractile Force Generationmentioning

confidence: 99%

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Acute and long-term effects of botulinum neurotoxin on the function and structure of developing extraocular muscles

Croes¹,

Baryshnikova²,

Kaluskar³

et al. 2007

Neurobiology of Disease

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Strabismus is a misalignment of the visual axes, due to an imbalance in extraocular muscle (EOM) function. Botulinum neurotoxin (BoNT) treatment can correct the misalignment with permanent therapeutic effects in infants, possibly because the toxin causes structural alterations in developing EOM. To determine whether BoNT indeed permanently weakens developing EOMs, we examined the chicken oculomotor system. Following injections of BoNT in hatchling chicks, we quantified physiological parameters (contractile force measurements) and morphological parameters (myofiber morphometry, innervation, quantitative transmission electron microscopy of mitochondria/fiber types). Treatment of developing EOM with BoNT caused acute reductions of muscle strength and mitochondrial densities, but minimal changes in muscle fiber diameter and neuromuscular junction structures. Contrary to expectations, contractile force was fully recovered by 3-4 months after treatment. Thus, permanent therapeutic effects of BoNT most likely do not cause permanent changes at the level of the peripheral effector organ, but rather involve central (CNS) adaptive responses.

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Section: Stimulation Parametersmentioning

confidence: 99%

Section: Contractile Force Generationmentioning

confidence: 99%

Acute and long-term effects of botulinum neurotoxin on the function and structure of developing extraocular muscles

Croes¹,

Baryshnikova²,

Kaluskar³

et al. 2007

Neurobiology of Disease

View full text Add to dashboard Cite

show abstract

Section: Nerve Stimulation-mentioning

confidence: 99%

“…Previous oculomotor model systems utilizing cats (Bach-y-Rita and Ito, 1966;Hanson and Lennerstrand, 1977;Shall and Goldberg, 1992;Dimitrova et al, 2002) and monkeys (Goldberg et al, 1998;Dimitrova et al, 2003) require removal of orbital bones to expose select extraocular muscles, craniotomy, and the use of stereotaxic parameters for the proper positioning of electrodes. A major disadvantage in using stereotaxic parameters is that one cannot directly visualize the nuclei or nerve that is to be stimulated.…”

Section: The Chicken As a Model System: Technical Aspects Of Nerve Acmentioning

confidence: 99%

Measurement of contractile force of skeletal and extraocular muscles: Effects of blood supply, muscle size and in situ or in vitro preparation

Croes

Bartheld

2007

Journal of Neuroscience Methods

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Contractile forces can be measured in situ and in vitro. To maintain metabolic viability with sufficient diffusion of oxygen, established guidelines for in vitro skeletal muscle preparations recommend use of relatively thin muscles (≤1.25 mm thick). Nevertheless, forces of thin extraocular muscles vary substantially between studies. Here, we examined parameters that affect force measurements of in situ and in vitro preparations, including blood supply, nerve stimulation, direct muscle stimulation, muscle size, oxygenated or non-oxygenated buffer solutions, and the time after interruption of vascular circulation. We found that the absolute forces of extraocular muscle are substantially lower when examined in vitro. In vitro preparation of 0.58 mm thick extraocular muscle from 3-week old birds underestimated contractile function, but not of thinner (0.33 mm) muscle from 2-day old birds. Our study shows that the effective criteria for functional viability, tested in vitro, differ between extraocular and other skeletal muscle. We conclude that contractile force of extraocular muscles will be underestimated by between 10 and 80%, when measurements are made after cessation of blood supply (at 5 -40 min). The mechanisms responsible for the declining values for force measurements are discussed, and we make specific recommendations for obtaining valid measurements of contractile force.

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“…The roughly 20 000 fibers per human rectus EOM surpasses requirements of conventionally recognized motility, 12 and suggests that individual EOMs might execute multiple functions using specialized fiber groups. Requisite for such functional diversity is anatomic diversity of innervation to different sets of fibers.…”

Section: Anatomic Evidence For Eom Compartmentalizationmentioning

confidence: 99%

Compartmentalization of extraocular muscle function

Demer

2014

Eye

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Ocular motor diversity exceeds capabilities of only six extraocular muscles (EOMs), but this deficiency is overcome by the plethora of fibers within individual EOMs surpassing requirements of homogeneous actuators. This paper reviews emerging evidence that regions of individual EOMs can be differentially innervated to exert independent oculorotary torques, broadening the oculomotor repertoire, and potentially explaining diverse strabismus pathophysiology. Parallel structure characterizes EOM and tendon fibers, with little transverse coupling of experimentally imposed or actively generated tension. This arrangement enables arbitrary groupings of tendon and muscle fibers to act relatively independently. Coordinated force generation among EOM fibers occurs only upon potentially mutable coordination of innervational commands, whose central basis is suggested by preliminary findings of apparent compartmental segregation of abducens motor neuron pools. Humans, monkeys, and other mammals demonstrate separate, nonoverlapping intramuscular nerve arborizations in the superior vs inferior compartments of the medial rectus (MR) and lateral rectus (LR) EOMs that could apply force at the superior vs inferior portions of scleral insertions, and in the medial vs lateral compartments of the superior oblique that act at the equatorial vs posterior scleral insertions that might preferentially implement incycloduction vs infraduction. Magnetic resonance imaging of the MR during several physiological ocular motor behaviors indicates differential compartmental function. Differential compartmental pathology can influence clinical strabismus. Partial abducens palsy commonly affects the superior LR compartment more than the inferior, inducing vertical strabismus that might erroneously be attributed to cyclovertical EOM pathology. Surgery may selectively manipulate EOM compartments.

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Extraocular Motor Unit and Whole-Muscle Responses in the Lateral Rectus Muscle of the Squirrel Monkey

Cited by 62 publications

References 45 publications

Acute and long-term effects of botulinum neurotoxin on the function and structure of developing extraocular muscles

Acute and long-term effects of botulinum neurotoxin on the function and structure of developing extraocular muscles

Measurement of contractile force of skeletal and extraocular muscles: Effects of blood supply, muscle size and in situ or in vitro preparation

Compartmentalization of extraocular muscle function

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