Ionic basis for the electro-responsiveness and oscillatory properties of guinea-pig thalamic neurones in vitro

J Physiol. 1984 Apr:349:227-47. doi: 10.1113/jphysiol.1984.sp015154.

Abstract

The ionic requirements for electro-responsiveness in thalamic neurones were studied using in vitro slice preparations of the guinea-pig diencephalon. Analysis of the current-voltage relationship in these neurones revealed delayed and anomalous rectification. Substitution of Na+ with choline in the bath or addition of tetrodotoxin (TTX) abolished the fast spikes and the plateau potentials, described in the accompanying paper. Ca2+ conductance blockage with Co2+, Cd2+ or Mn2+, or replacement of Ca2+ by Mg2+ abolished the low-threshold spikes (l.t.s.). Substitution with Ba2+ did not significantly increase the duration of the l.t.s., suggesting that under normal conditions the falling phase of this response is brought about by inactivation of the Ca2+ conductance. The after-hyperpolarization (a.h.p.) following fast spikes was markedly reduced in amplitude and duration by bath application of Cd2+, Co2+ or Mn2+, indicating that a large component of this response is generated by a Ca2+-dependent K+ conductance (gK[Ca]). Following hyperpolarizing current pulses, the membrane potential showed a delayed return to base line. This delay is produced by a transient K+ conductance as it can be modified by changing the drive force for K+. Presumptive intra-dendritic recording demonstrated high-threshold Ca2+ spikes (h.t.s.s.) which activate a gK[Ca]. Such h.t.s.s. were also seen at the somatic level when K+ conductance was blocked with 4-aminopyridine. It is proposed that the intrinsic biophysical properties of thalamic neurones allow them to serve as relay systems and as single cell oscillators at two distinct frequencies, 9-10 and 5-6 Hz. These frequencies coincide with the alpha and theta rhythms of the e.e.g. and, in the latter case, with the frequency of Parkinson's tremor.

Publication types

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

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Barium / pharmacology
  • Calcium / physiology
  • Cations / pharmacology*
  • Dendrites / physiology
  • Electric Conductivity
  • Electrophysiology
  • Guinea Pigs
  • In Vitro Techniques
  • Neurons / drug effects
  • Neurons / physiology*
  • Sodium / physiology
  • Tetrodotoxin / pharmacology
  • Thalamic Nuclei / drug effects
  • Thalamic Nuclei / physiology*

Substances

  • Cations
  • Barium
  • Tetrodotoxin
  • Sodium
  • Calcium