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Ariane Ménard"Gating of locomotor centre by the basal ganglia in the lamprey."

Abstract :

In mammals, it is known that GABAergic cells from the output nuclei of the basal ganglia tonically inhibit their target motor centres.
In the present study, the lamprey model was used to explore whether these interactions are present early in vertebrate evolution. We investigated the forebrain modulation of motor centres in lampreys, such as the diencephalic and the mesencephalic locomotor regions (DLR, MLR).
Our first aim was to identify forebrain GABAergic projections to these regions. GABAergic projections were found to originate from a population of neurones in the caudoventral portion of the medial pallium. The DLR and the MLR received also GABAergic projections from the lateral pallium and the striatum. In the pallium of amniotes, GABAergic neurones serve as interneurones and not as output neurones. The GABAergic projections from the caudoventral medial pallium and the ventral portion of the lateral pallium might thus be analogous to the mammalian output nuclei of the basal ganglia.
The second aim was to test the action of GABAergic inputs to the DLR and the MLR. In a semi-intact preparation, injections of GABA agonists into the MLR or the DLR, inhibited locomotion, whereas GABA antagonists initiated or facilitated locomotion. These results suggest that the above structures are under tonic inhibition at rest.
The third aim was to investigate the relationship of these GABAergic projections and the striatum. Electrical stimulation of the striatum induced a long plateau potential in reticulospinal cells associated with a locomotor episode. Moreover, the striatum sends axons to the area of the caudoventral medial pallium, as well as to the lateral pallium. 

Selected publications

Ménard A, Saitoh K, Grillner S. (2007) Role of the basal ganglia in the gating of the locomotion initiated by the diencephalic locomotor region in the lamprey. Manuscript
Thompson R, Ménard A, Pombal MA, Grillner S. (2007) Forebrain dopamine depletion impairs motor behavior in lamprey. J.Neurosci. Submitted
Saitoh K, Ménard A, Grillner S. (2007), Tectal control of locomotion, steering and eye movements in lamprey. J. Neurophysiol. Accepted
Robertson B, Auclair F, Ménard A, Grillner S, Dubuc R. (2007), The GABA Distribution in Lamprey is Phylogenetically Conserved. JCN Accepted
Ménard A, Auclair F, Bourcier C, Grillner S, Dubuc R. (2007), GABAergic Projections to the Mesencephalic Locomotor Region in the Lamprey Petromyzon marinus. JCN 501(2):260-73

Scientific focus :

I would like to investigate the neural mechanisms that take place in the basal ganglia and are responsible for selecting which basic motor program should be recruited at subcortical level in a given instant.

Thomas Boraud