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      Connections of the superior colliculus to shoulder muscles of the rat: a dual tracing study

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          Abstract

          Previous investigations indicate that the superior colliculus (SC) is involved in the initiation and execution of forelimb movements. In the present study we investigated the tectofugal, in particular the tecto-reticulo-spinal projections to the shoulder and arm muscles in the rat. We simultaneously retrogradely labeled the premotor neurons in the brainstem by injection of the pseudorabies virus PrV Bartha 614 into the m. rhomboideus minor and m. acromiodeltoideus, and anterogradely visualized the tectofugal projections by intracollicular injection of the tracer FITC dextrane. Our results demonstrate that the connection of the SC to the skeletal muscles of the forelimb is at least trisynaptic. This was confirmed by long survival times after virus injections into the muscles (98–101 h) after which numerous neurons in the deep layers of the SC were labeled. Transsynaptically retrogradely labeled brainstem neurons connected disynaptically to the injected muscles with adjacent tectal terminals were predominantly located in the gigantocellular nuclear complex of the reticular formation. In addition, putative relay neurons were found in the caudal part of the pontine reticular nucleus. Both tectal projections to the nucleus gigantocellularis and the pontine reticular nucleus were bilateral but ipsilaterally biased. We suggest this projection to be involved in more global functions in motivated behavior like general arousal allowing fast voluntary motor activity.

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          Most cited references61

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          Event or emergency? Two response systems in the mammalian superior colliculus.

          Recent studies of the effects of stimulating the superior colliculus (SC) in rodents suggest that this structure mediates at least two classes of response to novel sensory stimuli. One class contains the familiar orienting response, together with movements resembling tracking or pursuit, and appears appropriate for undefined sensory 'events'. The second class contains defensive movements such as avoidance or flight, together with cardiovascular changes, that would be appropriate for a sudden emergency such as the appearance of a predator, or of an object on collision course. The two response systems appear to depend on separate output projections, and are probably subject to different sensory and forebrain influences. These findings (1) suggest an explanation for the complex anatomical organization of the SC, with multiple output pathways differentially accessed by a very wide variety of inputs, (2) emphasize the similarities between the SC and the optic tectum in non-mammalian species, and (3) suggest that the SC may be useful as a model for studying both the sensory control of defensive responses, and how intelligent decisions can be taken about relatively simple sensory inputs.
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            Motor circuits in action: specification, connectivity, and function.

            Mammalian motor behavior is enabled by a hierarchy of interleaved circuit modules constructed by interneurons in the spinal cord, sensory feedback loops, and bilateral communication with supraspinal centers. Neuronal subpopulations are specified through a process of precisely timed neurogenesis, acquisition of transcriptional programs, and migration to spatially confined domains. Developmental and genetic programs instruct stereotyped and highly specific connectivity patterns, binding functionally distinct neuronal subpopulations into motor circuit modules at all hierarchical levels. Recent work demonstrates that spatial organization of motor circuits relates to precise connectivity patterns and that these patterns frequently correlate with specific behavioral functions of motor output. This Review highlights key examples of how developmental specification dictates organization of motor circuit connectivity and thereby controls movement. Copyright © 2012 Elsevier Inc. All rights reserved.
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              Circuits for skilled reaching and grasping.

              From an evolutionary perspective, it is clear that basic motor functions such as locomotion and posture are largely controlled by neural circuitries residing in the spinal cord and brain-stem. The control of voluntary movements such as skillful reaching and grasping is generally considered to be governed by neural circuitries in the motor cortex that connect directly to motoneurons via the corticomotoneuronal (CM) pathway. The CM pathway may act together with several brain-stem systems that also act directly with motoneurons. This simple view was challenged by work in the cat, which lacks the direct CM system, showing that the motor commands for reaching and grasping could be mediated via spinal interneurons with input from the motor-cortex and brain-stem systems. It was further demonstrated that the spinal interneurons mediating the descending commands for reaching and grasping constitute separate and distinct populations from those involved in locomotion and posture. The aim of this review is to describe populations of spinal interneurons that are involved in the control of skilled reaching and grasping in the cat, monkey, and human.
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                Author and article information

                Journal
                Front Neuroanat
                Front Neuroanat
                Front. Neuroanat.
                Frontiers in Neuroanatomy
                Frontiers Media S.A.
                1662-5129
                07 June 2013
                2013
                : 7
                : 17
                Affiliations
                [1] 1Allgemeine Zoologie and Neurobiologie, Ruhr-University Bochum Bochum, Germany
                [2] 2Brain Institute and Department of Physiology, School of Medicine, University of Utah Salt Lake City, UT, USA
                [3] 3Tierphysiologie, Ruhr-University Bochum Bochum, Germany
                Author notes

                Edited by: Alfonso Fairén, University Miguel Hernandez, Spain

                Reviewed by: Alino Martinez-Marcos, Universidad de Castilla, Spain; Peter Redgrave, University of Sheffield, UK

                *Correspondence: K.-P. Hoffmann, Tierphysiologie, Ruhr-University Bochum, Universitätsstr. 150, ND 5/26, 44780 Bochum, Germany e-mail: kphoffm@ 123456gmail.com
                Article
                10.3389/fnana.2013.00017
                3675767
                23760726
                a0898f1a-b215-43b4-b0a8-f4680a2f33fd
                Copyright © 2013 Rubelowski, Menge, Distler, Rothermel and Hoffmann.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.

                History
                : 12 March 2012
                : 22 May 2013
                Page count
                Figures: 10, Tables: 1, Equations: 0, References: 71, Pages: 15, Words: 8270
                Categories
                Neuroscience
                Original Research Article

                Neurosciences
                superior colliculus,m. rhomboideus,m. acromiodeltoideus,m. trapezius,pseudorabies virus,forelimb movements

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