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Descending GABAergic projections to the mesencephalic locomotor region in the lamprey Petromyzon marinus

Authors

  • Ariane Ménard,

    1. Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-17177 Stockholm, Sweden
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  • François Auclair,

    1. Département de Physiologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada
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  • Céline Bourcier-Lucas,

    1. Département de Physiologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada
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  • Sten Grillner,

    1. Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-17177 Stockholm, Sweden
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  • Réjean Dubuc

    Corresponding author
    1. Département de Physiologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada
    2. Département de Kinanthropologie, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada
    • Département de Kinanthropologie, Université du Québec à Montréal, C.P. 8888, succursale Centre-ville, Montréal, Québec H3C 3P8, Canada
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Abstract

The mesencephalic locomotor region (MLR) plays a significant role in the control of locomotion in all vertebrate species investigated. Forebrain neurons are likely to modulate MLR activity, but little is known about their inputs. Descending GABAergic projections to the MLR were identified by double-labeling neurons using Neurobiotin injected into the MLR combined with immunofluorescence against GABA. Several GABAergic projections to the MLR were identified in the telencephalon and diencephalon. The most abundant GABAergic projection to the MLR came from the caudal portion of the medial pallium, a region that may have similarities with the amygdala of higher vertebrates. A small population of GABAergic cells projecting to the MLR was found in the striatum and the ventral portion of the lateral pallium, which could respectively correspond to the input and output components of the basal ganglia thought to be involved in the selection of motor programs. Other GABAergic projections were found to come from the thalamus and the hypothalamus, which could take part in the motivational aspect of motor behavior in lampreys. Electrophysiological experiments were also carried out to examine the effects of GABA agonists and antagonists injected into the MLR in a semi-intact lamprey preparation. The GABA agonist inhibited locomotion, whereas the GABA antagonist initiated it. These results suggest that the GABAergic projections to the MLR modulate the activity of MLR neurons, which would be inhibited by GABA at rest. J. Comp. Neurol. 501:260–273, 2007. © 2007 Wiley-Liss, Inc.

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