title: Descending GABAergic projections to the mesencephalic locomotor region in the lamprey Petromyzon marinus.
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.
authors.affiliation: Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-17177 Stockholm, Sweden.
authors.forename: Ariane
authors.initials: A
authors.lastname: Ménard
authors.forename: François
authors.initials: F
authors.lastname: Auclair
authors.forename: Céline
authors.initials: C
authors.lastname: Bourcier-Lucas
authors.forename: Sten
authors.initials: S
authors.lastname: Grillner
authors.forename: Réjean
authors.initials: R
authors.lastname: Dubuc
mesh_terms: D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D005260:Female; D005455:Fluorescent Antibody Technique / Q000379:methods; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D007798:Lampreys; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008636:Mesencephalon / Q000033:anatomy & histology* / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects; D011724:Pyridazines / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018756:GABA Antagonists; D011724:Pyridazines; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; C049853:gabazine