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Bohlen MO, Warren S, May PJ. Is the central mesencephalic reticular formation a purely horizontal gaze center? Brain Struct Funct 2022; 227:2367-2393. [PMID: 35871423 DOI: 10.1007/s00429-022-02532-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 06/30/2022] [Indexed: 01/12/2023]
Abstract
Historically, the central mesencephalic reticular formation has been regarded as a purely horizontal gaze center based on the fact that electrical stimulation of this region produces horizontal saccades, it provides monosynaptic input to medial rectus motoneurons, and cells recorded in this region often display a peak in firing when horizontal saccades are made. We tested the proposition that the central mesencephalic reticular formation is purely a horizontal gaze center by examining whether this region also supplies terminals to superior rectus and levator palpebrae superioris motoneurons, both of which fire when making vertical eye movements. The experiments were carried out using dual tracer techniques at the light and electron microscopic level in macaque monkeys. Injections of biotinylated dextran amine or Phaseolus vulgaris leukoagglutinin into the central mesencephalic reticular formation produced anterogradely labeled terminals that were in synaptic contact with superior rectus and levator palpebrae superioris motoneurons that had been retrogradely labeled. These results indicate that this region is not purely connected with horizontal gaze motoneurons. In addition, we found that the number of contacts on vertical gaze motoneurons increased with more rostral injections involving the mesencephalic reticular formation adjacent to the interstitial nucleus of Cajal. This suggests that there is a caudal to rostral gradient for horizontal to vertical saccades, respectively, represented within the midbrain reticular formation. Finally, we utilized post-embedding immunohistochemistry to show that a portion of the labeled terminals were GABAergic, indicating they likely originate from downgaze premotor neurons.
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Affiliation(s)
- Martin O Bohlen
- Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - Susan Warren
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216, USA
| | - Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216, USA.
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Pastor AM, Blumer R, de la Cruz RR. Extraocular Motoneurons and Neurotrophism. Adv Neurobiol 2022; 28:281-319. [PMID: 36066830 DOI: 10.1007/978-3-031-07167-6_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Extraocular motoneurons are located in three brainstem nuclei: the abducens, trochlear and oculomotor. They control all types of eye movements by innervating three pairs of agonistic/antagonistic extraocular muscles. They exhibit a tonic-phasic discharge pattern, demonstrating sensitivity to eye position and sensitivity to eye velocity. According to their innervation pattern, extraocular muscle fibers can be classified as singly innervated muscle fiber (SIF), or the peculiar multiply innervated muscle fiber (MIF). SIF motoneurons show anatomical and physiological differences with MIF motoneurons. The latter are smaller and display lower eye position and velocity sensitivities as compared with SIF motoneurons.
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Affiliation(s)
- Angel M Pastor
- Departamento de Fisiología, Universidad de Sevilla, Seville, Spain.
| | - Roland Blumer
- Center of Anatomy and Cell Biology, Medical University of Vienna, Vienna, Austria
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Carrero-Rojas G, Hernández RG, Blumer R, de la Cruz RR, Pastor AM. MIF versus SIF Motoneurons, What Are Their Respective Contribution in the Oculomotor Medial Rectus Pool? J Neurosci 2021; 41:9782-9793. [PMID: 34675089 PMCID: PMC8612643 DOI: 10.1523/jneurosci.1480-21.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 08/18/2021] [Accepted: 10/11/2021] [Indexed: 12/18/2022] Open
Abstract
Multiply-innervated muscle fibers (MIFs) are peculiar to the extraocular muscles as they are non-twitch but produce a slow build up in tension on repetitive stimulation. The motoneurons innervating MIFs establish en grappe terminals along the entire length of the fiber, instead of the typical en plaque terminals that singly-innervated muscle fibers (SIFs) motoneurons establish around the muscle belly. MIF motoneurons have been proposed to participate only in gaze holding and slow eye movements. We aimed to discern the function of MIF motoneurons by recording medial rectus motoneurons of the oculomotor nucleus. Single-unit recordings in awake cats demonstrated that electrophysiologically-identified medial rectus MIF motoneurons participated in different types of eye movements, including fixations, rapid eye movements or saccades, convergences, and the slow and fast phases of the vestibulo-ocular nystagmus, the same as SIF motoneurons did. However, MIF medial rectus motoneurons presented lower firing frequencies, were recruited earlier and showed lower eye position (EP) and eye velocity (EV) sensitivities than SIF motoneurons. MIF medial rectus motoneurons were also smaller, had longer antidromic latencies and a lower synaptic coverage than SIF motoneurons. Peristimulus time histograms (PSTHs) revealed that electrical stimulation to the myotendinous junction, where palisade endings are located, did not recurrently affect the firing probability of medial rectus motoneurons. Therefore, we conclude there is no division of labor between MIF and SIF motoneurons based on the type of eye movement they subserve.SIGNIFICANCE STATEMENT In addition to the common singly-innervated muscle fiber (SIF), extraocular muscles also contain multiply-innervated muscle fibers (MIFs), which are non-twitch and slow in contraction. MIF motoneurons have been proposed to participate only in gaze holding and slow eye movements. In the present work, by single-unit extracellular recordings in awake cats, we demonstrate, however, that both SIF and MIF motoneurons, electrophysiologically-identified, participate in the different types of eye movements. However, MIF motoneurons showed lower firing rates (FRs), recruitment thresholds, and eye-related sensitivities, and could thus contribute to the fine adjustment of eye movements. Electrical stimulation of the myotendinous junction activates antidromically MIF motoneurons but neither MIF nor SIF motoneurons receive a synaptic reafferentation that modifies their discharge probability.
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Affiliation(s)
- Génova Carrero-Rojas
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Seville 41012, Spain
- Center of Anatomy and Cell Biology, Medical Imaging Cluster, Medical University Vienna, Vienna 1090, Austria
| | - Rosendo G Hernández
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Seville 41012, Spain
| | - Roland Blumer
- Center of Anatomy and Cell Biology, Medical Imaging Cluster, Medical University Vienna, Vienna 1090, Austria
| | - Rosa R de la Cruz
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Seville 41012, Spain
| | - Angel M Pastor
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Seville 41012, Spain
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Abstract
Eye movements are indispensable for visual image stabilization during self-generated and passive head and body motion and for visual orientation. Eye muscles and neuronal control elements are evolutionarily conserved, with novel behavioral repertoires emerging during the evolution of frontal eyes and foveae. The precise execution of eye movements with different dynamics is ensured by morphologically diverse yet complementary sets of extraocular muscle fibers and associated motoneurons. Singly and multiply innervated muscle fibers are controlled by motoneuronal subpopulations with largely selective premotor inputs from task-specific ocular motor control centers. The morphological duality of the neuromuscular interface is matched by complementary biochemical and molecular features that collectively assign different physiological properties to the motor entities. In contrast, the functionality represents a continuum where most motor elements contribute to any type of eye movement, although within preferential dynamic ranges, suggesting that signal transmission and muscle contractions occur within bands of frequency-selective pathways.
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Affiliation(s)
- Anja K E Horn
- Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University Munich, 80336 Munich, Germany;
| | - Hans Straka
- Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany
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Abstract
Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger-Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.
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Brysch C, Leyden C, Arrenberg AB. Functional architecture underlying binocular coordination of eye position and velocity in the larval zebrafish hindbrain. BMC Biol 2019; 17:110. [PMID: 31884959 PMCID: PMC6936144 DOI: 10.1186/s12915-019-0720-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 11/06/2019] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND The oculomotor integrator (OI) in the vertebrate hindbrain transforms eye velocity input into persistent position coding output, which plays a crucial role in retinal image stability. For a mechanistic understanding of the integrator function and eye position control, knowledge about the tuning of the OI and other oculomotor nuclei is needed. Zebrafish are increasingly used to study integrator function and sensorimotor circuits, yet the precise neuronal tuning to motor variables remains uncharacterized. RESULTS Here, we recorded cellular calcium signals while evoking monocular and binocular optokinetic eye movements at different slow-phase eye velocities. Our analysis reveals the anatomical distributions of motoneurons and internuclear neurons in the nucleus abducens as well as those of oculomotor neurons in caudally adjacent hindbrain volumes. Each neuron is tuned to eye position and/or velocity to variable extents and is only activated after surpassing particular eye position and velocity thresholds. While the abducens (rhombomeres 5/6) mainly codes for eye position, in rhombomeres 7/8, a velocity-to-position coding gradient exists along the rostro-caudal axis, which likely corresponds to the oculomotor structures storing velocity and position, and is in agreement with a feedforward mechanism of persistent activity generation. Position encoding neurons are recruited at eye position thresholds distributed across the behaviourally relevant dynamic range, while velocity-encoding neurons have more centred firing thresholds for velocity. In the abducens, neurons coding exclusively for one eye intermingle with neurons coding for both eyes. Many of these binocular neurons are preferentially active during conjugate eye movements and less active during monocular eye movements. This differential recruitment during monocular versus conjugate tasks represents a functional diversification in the final common motor pathway. CONCLUSIONS We localized and functionally characterized the repertoire of oculomotor neurons in the zebrafish hindbrain. Our findings provide evidence for a mixed but task-specific binocular code and suggest that generation of persistent activity is organized along the rostro-caudal axis in the hindbrain.
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Affiliation(s)
- Christian Brysch
- Werner Reichardt Centre for Integrative Neuroscience and Institute for Neurobiology, University of Tübingen, 72076, Tübingen, Germany
- Graduate Training Centre of Neuroscience, University of Tübingen, 72074, Tübingen, Germany
| | - Claire Leyden
- Werner Reichardt Centre for Integrative Neuroscience and Institute for Neurobiology, University of Tübingen, 72076, Tübingen, Germany
- Graduate Training Centre of Neuroscience, University of Tübingen, 72074, Tübingen, Germany
| | - Aristides B Arrenberg
- Werner Reichardt Centre for Integrative Neuroscience and Institute for Neurobiology, University of Tübingen, 72076, Tübingen, Germany.
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Chen Z, Fan G, Li A, Yuan J, Xu T. rAAV2-Retro Enables Extensive and High-Efficient Transduction of Lower Motor Neurons following Intramuscular Injection. Mol Ther Methods Clin Dev 2019; 17:21-33. [PMID: 31890738 PMCID: PMC6926343 DOI: 10.1016/j.omtm.2019.11.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 11/09/2019] [Indexed: 12/27/2022]
Abstract
The motor system controls muscle movement through lower motor neurons in the spinal cord and brainstem. Lower motor neurons are efferent neurons in the central nervous system (CNS) characterized by axonal projections that reach specific targets in the periphery. Lower motor neuron lesions result in the denervation and dysfunction of peripheral skeletal muscle. Great progress has been made to develop therapeutic strategies to transduce lower motor neurons with genes. However, the widespread distribution of lower motor neurons makes their specific, extensive, and efficient transduction a challenge. In this study, we demonstrated that, compared to the other tested recombinant adeno-associated virus (rAAV) serotypes, rAAV2-retro mediated the most efficient retrograde transduction of lower motor neurons in the spinal cord following intramuscular injection in neonatal mice. A single injection of rAAV2-retro in a single muscle enabled the efficient and extensive transduction of lower motor neurons in the spinal cord and brainstem rather than transducing only the lower motor neurons connected to the injected muscle. rAAV2-retro achieved the extensive transduction of lower motor neurons by the cerebrospinal fluid pathway. Our work suggests that gene delivery via the intramuscular injection of rAAV2-retro represents a promising tool in the development of gene therapy strategies for motor neuron diseases.
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Affiliation(s)
- Zhilong Chen
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.,MoE Key Laboratory for Biomedical Photonics, Collaborative Innovation Center for Biomedical Engineering, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan, China
| | - Guoqing Fan
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.,MoE Key Laboratory for Biomedical Photonics, Collaborative Innovation Center for Biomedical Engineering, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan, China
| | - Anan Li
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.,MoE Key Laboratory for Biomedical Photonics, Collaborative Innovation Center for Biomedical Engineering, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan, China
| | - Jing Yuan
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.,MoE Key Laboratory for Biomedical Photonics, Collaborative Innovation Center for Biomedical Engineering, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan, China
| | - Tonghui Xu
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.,MoE Key Laboratory for Biomedical Photonics, Collaborative Innovation Center for Biomedical Engineering, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan, China.,Institute of Life Sciences, Nanchang University, Nanchang, China
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Bohlen MO, El-Nahal HG, Sommer MA. Transduction of Craniofacial Motoneurons Following Intramuscular Injections of Canine Adenovirus Type-2 (CAV-2) in Rhesus Macaques. Front Neuroanat 2019; 13:84. [PMID: 31619971 PMCID: PMC6759538 DOI: 10.3389/fnana.2019.00084] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 09/02/2019] [Indexed: 11/21/2022] Open
Abstract
Reliable viral vector-mediated transgene expression in primate motoneurons would improve our ability to anatomically and physiologically interrogate motor systems. We therefore investigated the efficacy of replication defective, early region 1-deleted canine adenovirus type-2 (CAV-2) vectors for mediating transgene expression of fluorescent proteins into brainstem motoneurons following craniofacial intramuscular injections in four rhesus monkeys (Macaca mulatta). Vector injections were placed into surgically identified and isolated craniofacial muscles. After a 1- to 2-month survival time, animals were sacrificed and transgene expression was assessed with immunohistochemistry in the corresponding motoneuronal populations. We found that injections of CAV-2 into individual craniofacial muscles at doses in the range of ∼1010 to 1011 physical particles/muscle resulted in robust motoneuronal transduction and expression of immunohistochemically identified fluorescent proteins across multiple animals. By using different titers in separate muscles, with the resulting transduction patterns tracked via fluorophore expression and labeled motoneuron location, we established qualitative dose-response relationships in two animals. In one animal that received an atypically high titer (5.7 × 1011 total CAV-2 physical particles) distributed across numerous injection sites, no transduction was detected, likely due to a retaliatory immune response. We conclude that CAV-2 vectors show promise for genetic modification of primate motoneurons following craniofacial intramuscular injections. Our findings warrant focused attention toward the use of CAV-2 vectors to deliver opsins, DREADDs, and other molecular probes to improve genetics-based methods for primate research. Further work is required to optimize CAV-2 transduction parameters. CAV-2 vectors encoding proteins could provide a new, reliable route for modifying activity in targeted neuronal populations of the primate central nervous system.
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Affiliation(s)
- Martin O Bohlen
- Department of Biomedical Engineering, Duke University, Durham, NC, United States
| | - Hala G El-Nahal
- Department of Biomedical Engineering, Duke University, Durham, NC, United States
| | - Marc A Sommer
- Department of Biomedical Engineering, Duke University, Durham, NC, United States.,Department of Neurobiology, Duke University School of Medicine, Durham, NC, United States
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Lienbacher K, Sänger K, Strassburger S, Ehrt O, Rudolph G, Barnerssoi M, Horn AKE. Extraocular muscles involved in convergence are innervated by an additional set of palisade endings that may differ in their excitability: A human study. Prog Brain Res 2019; 248:127-137. [PMID: 31239126 DOI: 10.1016/bs.pbr.2019.04.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Palisade endings are located at the myotendinous junction of extraocular muscles in most mammals. Irrespective of their unclarified function as motor or sensory nerve endings, a specialized role in convergence is proposed, based on their high number in the medial rectus muscle (MR). Further support comes from a study in monkey demonstrating that only the MR and inferior rectus muscle (IR) contain an additional population of palisade endings that express the calcium-binding protein calretinin (CR) in addition to choline acetyltransferase (ChAT). Here we studied, whether CR-positive palisade endings are present in human as well and confined to extraocular muscles most active during convergence. The systematic analysis of all eye muscles of 17 human specimen revealed that only the MR and IR contain an additional population of CR-positive palisade endings and multiple en-grappe endings, which target non-twitch muscle fibers along their whole length. Approximately 80% of all palisade endings in the MR expressed CR. Furthermore, the intrafusal muscle fibers of some muscle spindles in the MR were innervated by CR-positive annulospiral nerve endings that transmit the signals of muscle length changes to the brain. All extraocular muscles contained few thin CR-positive, but ChAT-negative nerve fibers, possibly representing free sensory or autonomic endings arising from the trigeminal ganglion. As in monkey, in the medial periphery of the human oculomotor nucleus ChAT-positive neurons were found to co-express CR. Therefore these neurons most likely represent the cell bodies of CR-positive palisade endings in the MR. Unlike in monkey, these neurons do not lie within a compact cell group, but are more scattered. In conclusion, the MR and IR in human contain two histochemically different populations of palisade and multiple endings that may contribute to ocular alignment and convergence in a different way.
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Affiliation(s)
- Karoline Lienbacher
- Faculty of Medicine, Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University, Munich, Germany; Center for Vertigo and Balance Disorders DSGZ, Ludwig-Maximilians-University, Munich, Germany
| | - Kathrin Sänger
- Faculty of Medicine, Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University, Munich, Germany
| | - Sebastian Strassburger
- Faculty of Medicine, Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University, Munich, Germany
| | - Oliver Ehrt
- Department of Ophthalmology, University Hospital, Ludwig-Maximilians-University, Munich, Germany
| | - Günther Rudolph
- Department of Ophthalmology, University Hospital, Ludwig-Maximilians-University, Munich, Germany
| | - Miriam Barnerssoi
- Faculty of Medicine, Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University, Munich, Germany
| | - Anja K E Horn
- Faculty of Medicine, Institute of Anatomy and Cell Biology I, Ludwig-Maximilians-University, Munich, Germany; Center for Vertigo and Balance Disorders DSGZ, Ludwig-Maximilians-University, Munich, Germany.
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May PJ, Billig I, Gamlin PD, Quinet J. Central mesencephalic reticular formation control of the near response: lens accommodation circuits. J Neurophysiol 2019; 121:1692-1703. [PMID: 30840529 DOI: 10.1152/jn.00846.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To view a nearby target, the three components of the near response are brought into play: 1) the eyes are converged through contraction of the medial rectus muscles to direct both foveae at the target, 2) the ciliary muscle contracts to allow the lens to thicken, increasing its refractive power to focus the near target on the retina, and 3) the pupil constricts to increase depth of field. In this study, we utilized retrograde transsynaptic transport of the N2c strain of rabies virus injected into the ciliary body of one eye of macaque monkeys to identify premotor neurons that control lens accommodation. We previously used this approach to label a premotor population located in the supraoculomotor area. In the present report, we describe a set of neurons located bilaterally in the central mesencephalic reticular formation that are labeled in the same time frame as the supraoculomotor area population, indicating their premotor character. The labeled premotor neurons are mostly multipolar cells, with long, very sparsely branched dendrites. They form a band that stretches across the core of the midbrain reticular formation. This population appears to be continuous with the premotor near-response neurons located in the supraoculomotor area at the level of the caudal central subdivision of the oculomotor nucleus. The central mesencephalic reticular formation has previously been associated with horizontal saccadic eye movements, so these premotor cells might be involved in controlling lens accommodation during disjunctive saccades. Alternatively, they may represent a population that controls vergence velocity. NEW & NOTEWORTHY This report uses transsynaptic transport of rabies virus to provide new evidence that the central mesencephalic reticular formation (cMRF) contains premotor neurons controlling lens accommodation. When combined with other recent reports that the cMRF also contains premotor neurons supplying medial rectus motoneurons, these results indicate that this portion of the reticular formation plays an important role in directing the near response and disjunctive saccades when viewers look between targets located at different distances.
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Affiliation(s)
- Paul J May
- Department of Neurobiology and Anatomical Sciences, Department of Ophthalmology, and Department of Neurology, University of Mississippi Medical Center , Jackson, Mississippi
| | - Isabelle Billig
- Systems Neuroscience Center, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Paul D Gamlin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham , Birmingham, Alabama
| | - Julie Quinet
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham , Birmingham, Alabama
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Hernández RG, Calvo PM, Blumer R, de la Cruz RR, Pastor AM. Functional diversity of motoneurons in the oculomotor system. Proc Natl Acad Sci U S A 2019; 116:3837-46. [PMID: 30760592 DOI: 10.1073/pnas.1818524116] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Extraocular muscles contain two types of muscle fibers according to their innervation pattern: singly innervated muscle fibers (SIFs), similar to most skeletal muscle fibers, and multiply innervated muscle fibers (MIFs). Morphological studies have revealed that SIF and MIF motoneurons are segregated anatomically and receive different proportions of certain afferents, suggesting that while SIF motoneurons would participate in the whole repertoire of eye movements, MIF motoneurons would contribute only to slow eye movements and fixations. We have tested that proposal by performing single-unit recordings, in alert behaving cats, of electrophysiologically identified MIF and SIF motoneurons in the abducens nucleus. Our results show that both types of motoneuron discharge in relation to eye position and velocity, displaying a tonic-phasic firing pattern for different types of eye movement (saccades, vestibulo-ocular reflex, vergence) and gaze-holding. However, MIF motoneurons presented an overall reduced firing rate compared with SIF motoneurons, and had significantly lower recruitment threshold and also lower eye position and velocity sensitivities. Accordingly, MIF motoneurons could control mainly gaze in the off-direction, when less force is needed, whereas SIF motoneurons would contribute to increase muscle tension progressively toward the on-direction as more force is required. Anatomically, MIF and SIF motoneurons distributed intermingled within the abducens nucleus, with MIF motoneurons being smaller and having a lesser somatic synaptic coverage. Our data demonstrate the functional participation of both MIF and SIF motoneurons in fixations and slow and phasic eye movements, although their discharge properties indicate a functional segregation.
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12
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Lienbacher K, Ono S, Fleuriet J, Mustari M, Horn AKE. A Subset of Palisade Endings Only in the Medial and Inferior Rectus Muscle in Monkey Contain Calretinin. Invest Ophthalmol Vis Sci 2018; 59:2944-2954. [PMID: 30025142 PMCID: PMC5989861 DOI: 10.1167/iovs.18-24322] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 05/06/2018] [Indexed: 12/11/2022] Open
Abstract
Purpose To further chemically characterize palisade endings in extraocular muscles in rhesus monkeys. Methods Extraocular muscles of three rhesus monkeys were studied for expression of the calcium-binding protein calretinin (CR) in palisade endings and multiple endings. The complete innervation was visualized with antibodies against the synaptosomal-associated protein of 25 kDa and combined with immunofluorescence for CR. Six rhesus monkeys received tracer injections of choleratoxin subunit B or wheat germ agglutinin into either the belly or distal myotendinous junction of the medial or inferior rectus muscle to allow retrograde tracing in the C-group of the oculomotor nucleus. Double-immunofluorescence methods were used to study the CR content in retrogradely labeled neurons in the C-group. Results A subgroup of palisade and multiple endings was found to express CR, only in the medial and inferior rectus muscle. In contrast, the en plaque endings lacked CR. Accordingly, within the tracer-labeled neurons of the C-group, a subgroup expressed CR. Conclusions The study indicates that two different neuron populations targeting nontwitch muscle fibers are present within the C-group for inferior rectus and medial rectus, respectively, one expressing CR, one lacking CR. It is possible that the CR-negative neurons represent the basic population for all extraocular muscles, whereas the CR-positive neurons giving rise to CR-positive palisade endings represent a specialized, perhaps more excitable type of nerve ending in the medial and inferior rectus muscles, being more active in vergence. The malfunction of this CR-positive population of neurons that target nontwitch muscle fibers could play a significant role in strabismus.
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Affiliation(s)
- Karoline Lienbacher
- Institute of Anatomy and Cell Biology, Ludwig-Maximilians-Universität, Munich, Germany
- German Center for Vertigo and Balance Disorders, Klinikum Grosshadern, Ludwig-Maximilians Universität, Munich, Germany
| | - Seiji Ono
- Faculty of Health and Sport Science, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Jérome Fleuriet
- Washington National Primate Research Center, Seattle, Washington, United States
- Department of Ophthalmology, University of Washington, Seattle, Washington, United States
| | - Michael Mustari
- Washington National Primate Research Center, Seattle, Washington, United States
- Department of Ophthalmology, University of Washington, Seattle, Washington, United States
| | - Anja K. E. Horn
- Institute of Anatomy and Cell Biology, Ludwig-Maximilians-Universität, Munich, Germany
- German Center for Vertigo and Balance Disorders, Klinikum Grosshadern, Ludwig-Maximilians Universität, Munich, Germany
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13
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Park JH, Ahn JH, Choi SY, Cho JH, Lee TK, Kim IH, Lee JC, Choi JH, Hwang IK, Lee YJ, Lee E, Park S, Lim J, Seo K, Won MH. The location of projection neurons to the biceps brachii muscle in the telencephalon of the pigeon. Anat Histol Embryol 2017; 46:528-532. [DOI: 10.1111/ahe.12297] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Accepted: 08/06/2017] [Indexed: 01/16/2023]
Affiliation(s)
- J. H. Park
- Department of Biomedical Science and Research Institute for Bioscience and Biotechnology; Hallym University; Chuncheon South Korea
| | - J. H. Ahn
- Department of Biomedical Science and Research Institute for Bioscience and Biotechnology; Hallym University; Chuncheon South Korea
| | - S. Y. Choi
- Department of Biomedical Science and Research Institute for Bioscience and Biotechnology; Hallym University; Chuncheon South Korea
| | - J. H. Cho
- Department of Neurobiology; School of Medicine; Kangwon National University; Chuncheon South Korea
| | - T.-K. Lee
- Department of Neurobiology; School of Medicine; Kangwon National University; Chuncheon South Korea
| | - I. H. Kim
- Department of Neurobiology; School of Medicine; Kangwon National University; Chuncheon South Korea
| | - J.-C. Lee
- Department of Neurobiology; School of Medicine; Kangwon National University; Chuncheon South Korea
| | - J. H. Choi
- Department of Anatomy; College of Veterinary Medicine; Kangwon National University; Chuncheon South Korea
| | - I. K. Hwang
- Department of Anatomy and Cell Biology; College of Veterinary Medicine, and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
| | - Y. J. Lee
- Department of Emergency Medicine; Seoul Hospital; College of Medicine; Sooncheonhyang University; Seoul South Korea
| | - E. Lee
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
| | - S. Park
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
| | - J. Lim
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
| | - K. Seo
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
| | - M.-H. Won
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine and Research Institute for Veterinary Science; Seoul National University; Seoul South Korea
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14
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Bohlen MO, Warren S, May PJ. A central mesencephalic reticular formation projection to medial rectus motoneurons supplying singly and multiply innervated extraocular muscle fibers. J Comp Neurol 2017; 525:2000-2018. [PMID: 28177529 DOI: 10.1002/cne.24187] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 01/10/2017] [Accepted: 01/11/2017] [Indexed: 12/20/2022]
Abstract
We recently demonstrated a bilateral projection to the supraoculomotor area from the central mesencephalic reticular formation (cMRF), a region implicated in horizontal gaze changes. C-group motoneurons, which supply multiply innervated fibers in the medial rectus muscle, are located within the primate supraoculomotor area, but their inputs and function are poorly understood. Here, we tested whether C-group motoneurons in Macaca fascicularis monkeys receive a direct cMRF input by injecting this portion of the reticular formation with anterograde tracers in combination with injection of retrograde tracer into the medial rectus muscle. The results indicate that the cMRF provides a dense, bilateral projection to the region of the medial rectus C-group motoneurons. Numerous close associations between labeled terminals and each multiply innervated fiber motoneuron were present. Within the oculomotor nucleus, a much sparser ipsilateral projection onto some of the A- and B- group medial rectus motoneurons that supply singly innervated fibers was observed. Ultrastructural analysis demonstrated a direct synaptic linkage between anterogradely labeled reticular terminals and retrogradely labeled medial rectus motoneurons in all three groups. These findings reinforce the notion that the cMRF is a critical hub for oculomotility by proving that it contains premotor neurons supplying horizontal extraocular muscle motoneurons. The differences between the cMRF input patterns for C-group versus A- and B-group motoneurons suggest the C-group motoneurons serve a different oculomotor role than the others. The similar patterns of cMRF input to C-group motoneurons and preganglionic Edinger-Westphal motoneurons suggest that medial rectus C-group motoneurons may play a role in accommodation-related vergence.
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Affiliation(s)
- Martin O Bohlen
- Program in Neuroscience, University of Mississippi Medical Center, Jackson, Mississippi
| | - Susan Warren
- Department of Neurobiology & Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi
| | - Paul J May
- Department of Neurobiology & Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi.,Department of Ophthalmology, University of Mississippi Medical Center, Jackson, Mississippi.,Department of Neurology, University of Mississippi Medical Center, Jackson, Mississippi
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15
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Bohlen MO, Warren S, Mustari MJ, May PJ. Examination of feline extraocular motoneuron pools as a function of muscle fiber innervation type and muscle layer. J Comp Neurol 2016; 525:919-935. [PMID: 27588695 DOI: 10.1002/cne.24111] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 08/08/2016] [Accepted: 08/18/2016] [Indexed: 01/13/2023]
Abstract
This study explores two points related to the pattern of innervation of the extraocular muscles. First, species differences exist in the location of the motoneurons supplying multiply innervated fibers (MIFs) and singly innervated fibers (SIFs) in eye muscles. MIF motoneurons are located outside the extraocular nuclei in primates, but are intermixed with SIF motoneurons within rat extraocular nuclei. To test whether this difference is related to visual capacity and frontal placement of eyes, we injected retrograde tracers into the medial rectus muscle of the cat, a highly visual nonprimate with frontally placed eyes. Distal injections labeled smaller MIF motoneurons located ventrolaterally and rostrally within the oculomotor nucleus (III). More central injections also labeled a separate population of larger cells located dorsally in III. Thus, the cat shares with the nocturnal rat the feature of having MIF motoneurons located within the bounds of III. On the other hand, just as with monkeys, cats show segregation of the MIF and SIF medial rectus motoneuron pools, albeit in a different pattern. Second, extraocular muscles are divided into two layers; the inner, global layer inserts into the sclera, and the outer, orbital layer inserts into the connective tissue pulley. To test whether these layers are supplied by anatomically discrete motoneuron pools, we injected tracer into the orbital layer of the cat lateral rectus muscle. No evidence of either morphological or distributional differences was found, suggesting that the functional differences in these layers may be due mainly to their orbital anatomy, not their innervation. J. Comp. Neurol. 525:919-935, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Martin O Bohlen
- Program in Neuroscience, University of Mississippi Medical Center, Jackson, Mississippi, 39216
| | - Susan Warren
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, 39216
| | - Michael J Mustari
- National Primate Research Center, University of Washington, Seattle, Washington, 98195
| | - Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, 39216.,Department of Ophthalmology, University of Mississippi Medical Center, Jackson, Mississippi, 39216.,Department of Neurology, University of Mississippi Medical Center, Jackson, Mississippi, 39216
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16
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Blumer R, Maurer-Gesek B, Gesslbauer B, Blumer M, Pechriggl E, Davis-López de Carrizosa MA, Horn AK, May PJ, Streicher J, de la Cruz RR, Pastor ÁM. Palisade Endings Are a Constant Feature in the Extraocular Muscles of Frontal-Eyed, But Not Lateral-Eyed, Animals. Invest Ophthalmol Vis Sci 2016; 57:320-31. [PMID: 26830369 PMCID: PMC4826744 DOI: 10.1167/iovs.15-18716] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To test whether palisade endings are a general feature of mammalian extraocular muscles (EOMs). Methods Thirteen species, some frontal-eyed (human, monkey, cat, and ferret), and others lateral-eyed (pig, sheep, calf, horse, rabbit, rat, mouse, gerbil, and guinea pig) were analyzed. Palisade endings were labeled by using different combinations of immunofluorescence techniques. Three-dimensional reconstructions of immunolabeled palisade endings were done. Results In all frontal-eyed species, palisade endings were a consistent feature in the rectus EOMs. Their total number was high and they exhibited an EOM-specific distribution. In particular, the number of palisade endings in the medial recti was significantly higher than in the other rectus muscles. In the lateral-eyed animals, palisade endings were infrequent and, when present, their total number was rather low. They were only found in ungulates (sheep, calf, pig, and horse) and in rabbit. In rodents (rat, guinea pig, mouse, and gerbil) palisade endings were found infrequently (e.g., rat) or were completely absent. Palisade endings in frontal-eyed species and in some lateral-eyed species (pig, sheep, calf, and horse) had a uniform morphology. They generally lacked α-bungarotoxin staining, with a few exceptions in primates. Palisade endings in other lateral-eyed species (rabbit and rat) exhibited a simplified morphology and bound α-bungarotoxin. Conclusions Palisade endings are not a universal feature of mammalian EOMs. So, if they are proprioceptors, not all species require them. Because in frontal-eyed species, the medial rectus muscle has the highest number of palisade endings, they likely play a special role in convergence.
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Affiliation(s)
- Roland Blumer
- Center of Anatomy and Cell Biology Integrative Morphology Group, MIC, Medical University Vienna, Vienna, Austria
| | - Barbara Maurer-Gesek
- Center of Anatomy and Cell Biology Integrative Morphology Group, MIC, Medical University Vienna, Vienna, Austria
| | - Bernhard Gesslbauer
- CD-Laboratory for Extremity Reconstruction, Division of Plastic and Reconstructive Surgery, Medical University Vienna, Vienna, Austria
| | - Michael Blumer
- Division of Clinical and Functional Anatomy, Department of Anatomy, Histology and Embryology, Innsbruck Medical University, Innsbruck, Austria
| | - Elisabeth Pechriggl
- Division of Clinical and Functional Anatomy, Department of Anatomy, Histology and Embryology, Innsbruck Medical University, Innsbruck, Austria
| | | | - Anja K Horn
- Institute of Anatomy, Ludwig-Maximillian University, Munich, Germany
| | - Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, United States
| | - Johannes Streicher
- Center of Anatomy and Cell Biology Integrative Morphology Group, MIC, Medical University Vienna, Vienna, Austria 7Karl Landsteiner University of Health Sciences, Krems an der Donau, Austria
| | - Rosa R de la Cruz
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Ángel M Pastor
- Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
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May PJ, Warren S, Bohlen MO, Barnerssoi M, Horn AKE. A central mesencephalic reticular formation projection to the Edinger-Westphal nuclei. Brain Struct Funct 2015; 221:4073-4089. [PMID: 26615603 DOI: 10.1007/s00429-015-1147-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 11/12/2015] [Indexed: 11/30/2022]
Abstract
The central mesencephalic reticular formation, a region associated with horizontal gaze control, has recently been shown to project to the supraoculomotor area in primates. The Edinger-Westphal nucleus is found within the supraoculomotor area. It has two functionally and anatomically distinct divisions: (1) the preganglionic division, which contains motoneurons that control both the actions of the ciliary muscle, which focuses the lens, and the sphincter pupillae muscle, which constricts the iris, and (2) the centrally projecting division, which contains peptidergic neurons that play a role in food and fluid intake, and in stress responses. In this study, we used neuroanatomical tracers in conjunction with immunohistochemistry in Macaca fascicularis monkeys to examine whether either of these Edinger-Westphal divisions receives synaptic input from the central mesencephalic reticular formation. Anterogradely labeled reticular axons were observed making numerous boutonal associations with the cholinergic, preganglionic motoneurons of the Edinger-Westphal nucleus. These associations were confirmed to be synaptic contacts through the use of confocal and electron microscopic analysis. The latter indicated that these terminals generally contained pleomorphic vesicles and displayed symmetric, synaptic densities. Examination of urocortin-1-positive cells in the same cases revealed fewer examples of unambiguous synaptic relationships, suggesting the centrally projecting Edinger-Westphal nucleus is not the primary target of the projection from the central mesencephalic reticular formation. We conclude from these data that the central mesencephalic reticular formation must play a here-to-for unexpected role in control of the near triad (vergence, lens accommodation and pupillary constriction), which is used to examine objects in near space.
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Affiliation(s)
- Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, MS, 39216, USA
- Department of Ophthalmology, University of Mississippi Medical Center, Jackson, MS, 39216, USA
- Department of Neurology, University of Mississippi Medical Center, Jackson, MS, 39216, USA
| | - Susan Warren
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, MS, 39216, USA
| | - Martin O Bohlen
- Department of Program in Neuroscience, University of Mississippi Medical Center, Jackson, MS, 39216, USA
| | - Miriam Barnerssoi
- Institute of Anatomy and Cell Biology I, Ludwig-Maximilians University, Pettenkoferstrasse 11, 80336, Munich, Germany
| | - Anja K E Horn
- Institute of Anatomy and Cell Biology I, Ludwig-Maximilians University, Pettenkoferstrasse 11, 80336, Munich, Germany.
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Zeeh C, Mustari MJ, Hess BJM, Horn AKE. Transmitter inputs to different motoneuron subgroups in the oculomotor and trochlear nucleus in monkey. Front Neuroanat 2015; 9:95. [PMID: 26257611 PMCID: PMC4513436 DOI: 10.3389/fnana.2015.00095] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 07/06/2015] [Indexed: 11/13/2022] Open
Abstract
In all vertebrates the eyes are moved by six pairs of extraocular muscles enabling horizontal, vertical and rotatory movements. Recent work showed that each extraocular muscle is controlled by two motoneuronal groups: (1) Motoneurons of singly-innervated muscle fibers (SIF) that lie within the boundaries of motonuclei mediating a fast muscle contraction; and (2) motoneurons of multiply-innervated muscle fibers (MIF) in the periphery of motonuclei mediating a tonic muscle contraction. Currently only limited data about the transmitter inputs to the SIF and MIF motoneurons are available. Here we performed a quantitative study on the transmitter inputs to SIF and MIF motoneurons of individual muscles in the oculomotor and trochlear nucleus in monkey. Pre-labeled motoneurons were immunostained for GABA, glutamate decarboxylase, GABA-A receptor, glycine transporter 2, glycine receptor 1, and vesicular glutamate transporters 1 and 2. The main findings were: (1) the inhibitory control of SIF motoneurons for horizontal and vertical eye movements differs. Unlike in previous primate studies a considerable GABAergic input was found to all SIF motoneuronal groups, whereas a glycinergic input was confined to motoneurons of the medial rectus (MR) muscle mediating horizontal eye movements and to those of the levator palpebrae (LP) muscle elevating the upper eyelid. Whereas SIF and MIF motoneurons of individual eye muscles do not differ numerically in their GABAergic, glycinergic and vGlut2 input, vGlut1 containing terminals densely covered the supraoculomotor area (SOA) targeting MR MIF motoneurons. It is reasonable to assume that the vGlut1 input affects the near response system in the SOA, which houses the preganglionic neurons mediating pupillary constriction and accommodation and the MR MIF motoneurones involved in vergence.
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Affiliation(s)
- Christina Zeeh
- Institute of Anatomy and Cell Biology, Department I, Ludwig-Maximilians UniversityMunich, Germany
| | - Michael J. Mustari
- Washington National Primate Research Center and Department of Ophthalmology, University of WashingtonSeattle, WA, USA
| | - Bernhard J. M. Hess
- Vestibulo-Oculomotor Laboratory Zürich, Department of Neurology, University HospitalZürich, Switzerland
| | - Anja K. E. Horn
- Institute of Anatomy and Cell Biology, Department I, Ludwig-Maximilians UniversityMunich, Germany
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