title: Noncholinergic excitatory actions of motoneurons in the neonatal mammalian spinal cord.
abstract: Mammalian spinal motoneurons are considered to be output elements of the spinal cord that generate exclusively cholinergic actions on Renshaw cells, their intraspinal synaptic targets. Here, we show that antidromic stimulation of motor axons evokes depolarizing monosynaptic potentials in Renshaw cells that are depressed, but not abolished, by cholinergic antagonists. This residual potential was abolished by 2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. In the presence of cholinergic antagonists, motor axon stimulation triggered locomotor-like activity that was blocked by 2-amino-5-phosphonovaleric acid. Some cholinergic motoneuronal terminals on both Renshaw cells and motoneurons were enriched in glutamate, but none expressed vesicular glutamate transporters. Our results raise the possibility that motoneurons release an excitatory amino acid in addition to acetylcholine and that they may be more directly involved in the genesis of mammalian locomotion than previously believed.
authors.affiliation: Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. mentisg@ninds.nih.gov
authors.forename: George Z
authors.initials: GZ
authors.lastname: Mentis
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Alvarez
authors.forename: Agnes
authors.initials: A
authors.lastname: Bonnot
authors.forename: Dannette S
authors.initials: DS
authors.lastname: Richards
authors.forename: David
authors.initials: D
authors.lastname: Gonzalez-Forero
authors.forename: Ricardo
authors.initials: R
authors.lastname: Zerda
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Donovan
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000109:Acetylcholine; D000818:Animals; D000831:Animals, Newborn; D018680:Cholinergic Antagonists / Q000494:pharmacology*; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D018698:Glutamic Acid / Q000378:metabolism; D007150:Immunohistochemistry; D008124:Locomotion / Q000187:drug effects; D051379:Mice; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism; D013116:Spinal Cord / Q000502:physiology*
chemical_list: D018680:Cholinergic Antagonists; D018698:Glutamic Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D000109:Acetylcholine