Voltage-gated ionic currents and their roles in timing coding in auditory neurons of the nucleus magnocellularis of the chick

Neurosci Res. 1996 Sep;26(1):29-45. doi: 10.1016/0168-0102(96)01071-1.


Avian cochlear neurons of the nucleus magnocellularis (NMC) are known to encode temporal information of sound. The neuron generated only a single action potential at a stable timing even though suprathreshold currents of long duration (> 100 ms) was injected. The threshold for the action potential was -42 mV. In voltage-clamp experiments, a TTX-sensitive Na current was activated at membrane potentials more positive than -50 mV. A low voltage activated (LVA) Ca current and a high voltage activated (HVA) Ca current were observed. The LVA Ca current was activated from -65 mV and showed a voltage dependent inactivation. The HVA Ca current was activated from -40 mV and did not show any inactivation. The LVA Ca current and the HVA Ca current were sensitive to Ni2+ (0.1 mM) and Nifedipine (10-20 mM), respectively. NMC neurons showed a TEA-sensitive K current and a 4-AP-sensitive K current. With 4-AP (0.5 mM) in a bathing medium, the threshold of action potential was decreased to -49 mV and the timing of action potential generation showed a wider distribution than that of control. Ni2+ (0.1 mM) reversed effects of 4-AP on the threshold and the variability of action potential onsets. It is concluded that a 4-AP-sensitive current counteracts the LVA Ca current that facilitates Na spike generation, and sets a threshold to a higher level for generating a single action potential at a precise timing following synaptic inputs from the auditory nerve.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Animals
  • Calcium Channels / physiology
  • Chick Embryo
  • Cochlear Nucleus / cytology*
  • Cochlear Nucleus / physiology
  • Evoked Potentials, Auditory, Brain Stem
  • Ion Channel Gating / physiology*
  • Ion Channels / physiology*
  • Kinetics
  • Neurons, Afferent / chemistry
  • Neurons, Afferent / physiology*
  • Nickel / pharmacology
  • Potassium Channel Blockers
  • Potassium Channels / physiology
  • Sodium Channels / physiology
  • Synaptic Transmission / physiology
  • Tetraethylammonium
  • Tetraethylammonium Compounds / pharmacology
  • Tetrodotoxin / pharmacology
  • Time Factors
  • Vestibulocochlear Nerve / cytology*
  • Vestibulocochlear Nerve / physiology


  • Calcium Channels
  • Ion Channels
  • Potassium Channel Blockers
  • Potassium Channels
  • Sodium Channels
  • Tetraethylammonium Compounds
  • Tetrodotoxin
  • Tetraethylammonium
  • Nickel
  • 4-Aminopyridine