HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 577/3/879    most recent jphysiol.2006.117622v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Yanovsky, Y. Articles by Misgeld, U. Search for Related Content PubMed PubMed Citation Articles by Yanovsky, Y. Articles by Misgeld, U. Related Collections Neuroscience

¹ Institut für Physiologie und Pathophysiologie und Interdisziplinäres Zentrum für Neurowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany

A phasic activation of small-conductance Ca²⁺-dependent K⁺ channels (SK channels) underlies spike-afterhyperpolarizations and spike-independent, transient hyperpolarizations in juvenile substantia nigra neurons. Outward current pulses that cause the spike-independent hyperpolarizations result from ryanodine receptor-mediated Ca²⁺ release from intracellular stores. To study the modulation of excitability by the outward current pulses, we recorded from GABAergic pars reticulata neurons of mice at postnatal days 12–16. We induced a prolongation of SK channel open states by 1-ethyl-2-benzimidazolinone (1-EBIO). In addition to a prolongation of spike-afterhyperpolarizations, 1-EBIO (200 µM) potentiated outward current pulses by increasing their duration. Neurons were manipulated by current injection to display continuous or discontinuous discharge. Despite the prolongation of the outward current pulses by 1-EBIO, continuous action potential discharge became more regular, although its frequency declined. Durations of silent periods (periods of >2x average interspike interval) increased. Caffeine (1 mM) further increased the duration of such silent periods. Caffeine, however, had no effect at short interspike intervals (<600 ms). Cyclopiazonic acid (10 µM) silenced discharge in 1-EBIO, but discharge reappeared with the depletion of Ca²⁺ stores. We conclude that the modulation of excitability by an activation of SK channels through ryanodine receptor-mediated release of Ca²⁺ critically depends on the frequency of discharge. Outward current pulses occur only if interspike intervals exceed the duration of spike-afterhyperpolarizations. In this instance, the phasic, spike-independent activation of SK channels supports pauses to interrupt autonomous discharge in juvenile GABAergic pars reticulata neurons.

(Received 20 July 2006; accepted after revision 12 October 2006; first published online 19 October 2006)
Corresponding author U. Misgeld: Institut für Physiologie und Pathophysiologie, Universität Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany. Email: ulrich.misgeld{at}physiologie.uni-heidelberg.de