Voltage-dependent burst-to-tonic switching of thalamic cell activity: an in vitro study.
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.
D000818:Animals; D002118:Calcium / Q000502:physiology; D005071:Evoked Potentials; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D012964:Sodium / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013788:Thalamus / Q000502:physiology*
D007473:Ion Channels; D013779:Tetrodotoxin; D012964:Sodium; D011188:Potassium; D002118:Calcium