Nicotinic activation of reticulospinal cells involved in the control of swimming in lampreys

Authors

  • Didier Le Ray,

    1. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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    • Present address: Laboratoire de Neurobiologie des Réseaux, CNRS-UMR5816, 33405 Talence, France

  • Frédéric Brocard,

    1. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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  • Céline Bourcier-Lucas,

    1. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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    • Note: This author performed all anatomical studies

  • François Auclair,

    1. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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  • Philippe Lafaille,

    1. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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  • Réjean Dubuc

    1. Département de kinanthropologie, Université du Québec à Montréal, H3C 3P8
    2. Centre de Recherche en Sciences Neurologiques, Université de Montréal, Montréal Québec, Canada, H3C 3J7
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: Dr Réjean Dubuc, 1Département de Kinanthropologie, as above. E-mail: dubuc.rejean@uqam.ca

Abstract

In lampreys as in other vertebrates, brainstem centres play a key role in the initiation and control of locomotion. One such centre, the mesencephalic locomotor region (MLR), was identified physiologically at the mesopontine border. Descending inputs from the MLR are relayed by reticulospinal neurons in the pons and medulla, but the mechanisms by which this is carried out remain unknown. Because previous studies in higher vertebrates and lampreys described cholinergic cells within the MLR region, we investigated the putative role of cholinergic agonists in the MLR-controlled locomotion. The local application of either acetylcholine or nicotine exerted a direct dose-dependent excitation on reticulospinal neurons as well as induced active or fictive locomotion. It also accelerated ongoing fictive locomotion. Choline acetyltransferase-immunoreactive cells were found in the region identified as the MLR of lampreys and nicotinic antagonists depressed, whereas physostigmine enhanced the compound EPSP evoked in reticulospinal neurons by electrical stimulation of this region. In addition, cholinergic inputs from the MLR to reticulospinal neurons were found to be monosynaptic. When the brainstem was perfused with d-tubocurarine, the induction of swimming by MLR stimulation was depressed, but not prevented, in a semi-intact preparation. Altogether, the results support the hypothesis that cholinergic inputs from the MLR to reticulospinal cells play a substantial role in the initiation and the control of locomotion.

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