Potassium currents dynamically set the recruitment and firing properties of F-type motoneurons in neonatal mice.
In neonatal mice, fast- and slow-type motoneurons display different patterns of discharge. In response to a long liminal current pulse, the discharge is delayed up to several seconds in fast-type motoneurons and their firing frequency accelerates. In contrast, slow-type motoneurons discharge immediately, and their firing frequency decreases at the beginning of the pulse. Here, we identify the ionic currents that underlie the delayed firing of fast-type motoneurons. We find that the firing delay is caused by a combination of an A-like potassium current that transiently suppresses firing on a short time scale and a slowly-inactivating potassium current that inhibits the discharge over a much longer time scale. We then show how these intrinsic currents dynamically shape the discharge threshold and the frequency-input function of fast-type motoneurons. These currents contribute to the orderly recruitment of motoneurons in neonates and might play a role in the postnatal maturation of motor units.
Centre de Neurophysique, Physiologie et Pathologie, Université Paris Descartes, Centre National de la Recherche Scientifique (UMR 8119), Paris, France felxfel@aol.com.
Félix
http://orcid.org/0000-0003-1715-3233
F
Leroy
Centre de Neurophysique, Physiologie et Pathologie, Université Paris Descartes, Centre National de la Recherche Scientifique (UMR 8119), Paris, France.
Boris
http://orcid.org/0000-0003-4221-7526
B
Lamotte d'Incamps
Centre de Neurophysique, Physiologie et Pathologie, Université Paris Descartes, Centre National de la Recherche Scientifique (UMR 8119), Paris, France.
Daniel
http://orcid.org/0000-0002-0431-9604
D
Zytnicki
D000200:Action Potentials; D000818:Animals; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000378:metabolism; D011999:Recruitment, Neurophysiological
D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D011188:Potassium
functional properties; potassium currents; spinal motoneurons subtypes