Potassium currents dynamically set the recruitment and firing properties of F-type motoneurons in neonatal mice

J Neurophysiol. 2015 Sep;114(3):1963-73. doi: 10.1152/jn.00193.2015. Epub 2015 Aug 12.


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.

Keywords: functional properties; potassium currents; spinal motoneurons subtypes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials*
  • Animals
  • Female
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Motor Neurons / drug effects
  • Motor Neurons / physiology*
  • Potassium / metabolism*
  • Potassium Channel Blockers / pharmacology
  • Potassium Channels, Voltage-Gated / antagonists & inhibitors
  • Potassium Channels, Voltage-Gated / metabolism
  • Recruitment, Neurophysiological*


  • Potassium Channel Blockers
  • Potassium Channels, Voltage-Gated
  • Potassium