Voltage-dependent burst-to-tonic switching of thalamic cell activity: an in vitro study

Arch Ital Biol. 1984 Mar;122(1):73-82.


The electroresponsiveness of mammalian thalamic neurons was studied in a slice preparation of the guinea pig diencephalon. Although the morphology of the cells varied, their electroresponsive properties were the same. Stimulation of thalamic cells at a membrane potential more negative than--60 mV produced burst responses and stimulation of more depolarized levels produced tonic firing of fast spikes. The burst response is generated by an inactivating Ca++-conductance. It is seen as a slow Ca++-spike which in turn triggers fast Na+-spikes. The Ca++-conductance is deinactivated by hyperpolarization beyond--60 mV. The membranes of thalamic neurons contain a number of other conductances including a Ca++-dependent K+-conductance producing spike afterhyperpolarization and a non-inactivating Na+-conductance which plays an important role during tonic activity of the cells. The early part of a response to a long-lasting stimulus given at rest or at a hyperpolarized level is dominated by the burst and thus is is independent of the stimulus amplitude. During the late part of such a response the firing rate is highly dependent of the stimulus intensity. Current-frequency plots for the first inter-spike intervals after the burst during long stimuli are upward convex, but after "steady-state" is reached the plots are almost linear.

MeSH terms

  • Animals
  • Calcium / physiology
  • Evoked Potentials
  • Guinea Pigs
  • In Vitro Techniques
  • Ion Channels / physiology
  • Membrane Potentials
  • Neurons / drug effects
  • Neurons / physiology*
  • Potassium / physiology
  • Sodium / physiology
  • Tetrodotoxin / pharmacology
  • Thalamus / physiology*


  • Ion Channels
  • Tetrodotoxin
  • Sodium
  • Potassium
  • Calcium