title: The mesencephalic locomotor region sends a bilateral glutamatergic drive to hindbrain reticulospinal neurons in a tetrapod.
abstract: In vertebrates, stimulation of the mesencephalic locomotor region (MLR) on one side evokes symmetrical locomotor movements on both sides. How this occurs was previously examined in detail in a swimmer using body undulations (lamprey), but in tetrapods the downstream projections from the MLR to brainstem neurons are not fully understood. Here we examined the brainstem circuits from the MLR to identified reticulospinal neurons in the salamander Notophthalmus viridescens. Using neural tracing, we show that the MLR sends bilateral projections to the middle reticular nucleus (mRN, rostral hindbrain) and the inferior reticular nucleus (iRN, caudal hindbrain). Ca(2+) imaging coupled to electrophysiology in in vitro isolated brains revealed very similar responses in reticulospinal neurons on both sides to a unilateral MLR stimulation. As the strength of MLR stimulation was increased, the responses increased in size in reticulospinal neurons of the mRN and iRN, but the responses in the iRN were smaller. Bath-application or local microinjections of glutamatergic antagonists markedly reduced reticulospinal neuron responses, indicating that the MLR sends glutamatergic inputs to reticulospinal neurons. In addition, reticulospinal cells responded to glutamate microinjections and the size of the responses paralleled the amount of glutamate microinjected. Immunofluorescence coupled with anatomical tracing confirmed the presence of glutamatergic projections from the MLR to reticulospinal neurons. Overall, we show that the brainstem circuits activated by the MLR in the salamander are organized similarly to those previously described in lampreys, indicating that the anatomo-physiological features of the locomotor drive are well conserved in vertebrates. J. Comp. Neurol. 524:1361-1383, 2016. © 2015 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc.
authors.affiliation: Groupe de Recherche sur le Système Nerveux Central, Département de neurosciences, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Ryczko
authors.affiliation: Groupe de Recherche sur le Système Nerveux Central, Département de neurosciences, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Francois
authors.initials: F
authors.lastname: Auclair
authors.affiliation: INSERM U862 - Neurocentre Magendie, Motor System Diseases Team, Bordeaux Cedex, France.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Cabelguen
authors.affiliation: Groupe de Recherche sur le Système Nerveux Central, Département de neurosciences, Université de Montréal, Montréal, Québec, Canada.|Groupe de Recherche en Activité Physique Adaptée, Département des sciences de l'activité physique, Université du Québec à Montréal, Québec, Canada.
authors.forename: Réjean
authors.initials: R
authors.lastname: Dubuc
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001933:Brain Stem / Q000166:cytology*; D002118:Calcium / Q000378:metabolism; D002452:Cell Count; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D007839:Functional Laterality; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D014562:Caudata / Q000033:anatomy & histology*; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D003911:Dextrans; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C056639:2-amino-5-phosphopentanoic acid; D002795:Choline O-Acetyltransferase; D014633:Valine; D002118:Calcium
keywords: brainstem; conservation; locomotor circuits; salamander