Mechanisms of excitation of spinal networks by stimulation of the ventral roots.
It has recently been demonstrated that motoneurons in neonatal rodents release an excitatory amino acid, in addition to acetylcholine, from their central terminals onto Renshaw cells. Although the function of this amino acid release is not understood, it may mediate the excitatory actions of motor axon stimulation on spinal motor networks. Stimulation of motor axons in the ventral roots or muscle nerves can activate the locomotor central pattern generator or entrain bursting in the disinhibited cord. Both of these effects persist in the presence of cholinergic antagonists and are abolished or diminished by ionotropic and metabotropic glutamate antagonists. Calcium imaging in the disinhibited cord shows that a ventral root stimulus evokes ventrolateral activity initially, which subsequently propagates to the rest of the cord. This finding suggests that excitatory interneurons excited by motoneuron recurrent collaterals are located in this region. However, motoneurons do not exhibit short latency excitatory potentials in response to ventral root stimulation indicating that the excitatory effects are mediated polysynaptically. We discuss the significance of these findings.
Developmental Neurobiology Section, NINDS, NIH, Bethesda, Maryland, USA. odonovm@ninds.nih.gov
Michael J
MJ
O'Donovan
Agnes
A
Bonnot
George Z
GZ
Mentis
Nikolai
N
Chub
Avinash
A
Pujala
Francisco J
FJ
Alvarez
D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000187:drug effects / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology; D002645:Chickens; D018680:Cholinergic Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D008124:Locomotion / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation; D051381:Rats; D013116:Spinal Cord / Q000502:physiology*; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D018680:Cholinergic Antagonists; D018756:GABA Antagonists; D013331:Strychnine; D001640:Bicuculline