Ionic and synaptic mechanisms underlying a brainstem oscillator: an in vitro study of the pacemaker nucleus of Apteronotus

J Comp Physiol A. 1991 May;168(5):521-32. doi: 10.1007/BF00215074.


1. In an in vitro preparation of the medullary pacemaker nucleus of Apteronotus, the consequences of a variety of ionic and pharmacological manipulations upon both ongoing activity and synaptic modulation of the nucleus were assessed. 2. Spontaneous rhythmicity in the pacemaker nucleus was found to be Na+-, K+-, and Ca(2+)-dependent. The extreme sensitivity to 4-aminopyridine (4-AP) relative to other treatments suggested that the K+ A-current is a critical element in the oscillations. 3. Elevated K+ or 4-AP were titrated to concentrations that suppressed spontaneous oscillations, but allowed modulatory, 'chirp' epsps to persist. The transition to elevated K+ revealed oscillatory properties in some neurons in the form of epsp-induced ringing 4. Threshold concentrations of 4-AP sufficient to halt oscillations, caused epsps to become larger and complex, increased input resistance, and enhanced the effects of current injection on epsp amplitude. A greater degree of voltage-sensitivity was also seen in later components of the complex epsp. 5. Several treatments presumed to increase Ca2+ caused desynchronization of firing and revealed diverging intrinsic frequencies among cells.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Animals
  • Biological Clocks / drug effects
  • Biological Clocks / physiology*
  • Brain Stem / drug effects
  • Brain Stem / growth & development
  • Brain Stem / physiology*
  • Calcium / pharmacology
  • Cold Temperature
  • Electric Fish / physiology*
  • Fourier Analysis
  • Glutamates / pharmacology
  • Glutamic Acid
  • Humans
  • In Vitro Techniques
  • Potassium Channels / drug effects
  • Sodium Channels / drug effects
  • Sodium Channels / metabolism
  • Synapses / drug effects
  • Synapses / physiology
  • Tetrodotoxin / pharmacology


  • Glutamates
  • Potassium Channels
  • Sodium Channels
  • Glutamic Acid
  • Tetrodotoxin
  • 4-Aminopyridine
  • Calcium