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The Journal of Neurophysiology Vol. 86 No. 6 December 2001, pp. 2878-2886
Copyright ©2001 by the American Physiological Society
Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid 28002, Spain
Martín, Eduardo D.,
Alfonso Araque, and
Washington Buño.
Synaptic Regulation of the Slow Ca2+-Activated
K+ Current in Hippocampal CA1 Pyramidal Neurons:
Implication in Epileptogenesis. J. Neurophysiol. 86: 2878-2886, 2001. The slow
Ca2+-activated K+ current (sIAHP)
plays a critical role in regulating neuronal excitability, but its
modulation during abnormal bursting activity, as in epilepsy, is
unknown. Because synaptic transmission is enhanced during epilepsy, we
investigated the synaptically mediated regulation of the
sIAHP and its control of neuronal excitability during
epileptiform activity induced by 4-aminopyridine (4AP) or
4AP+Mg2+-free treatment in rat hippocampal slices. We used
electrophysiological and photometric Ca2+ techniques to
analyze the sIAHP modifications that parallel epileptiform activity. Epileptiform activity was characterized by slow, repetitive, spontaneous depolarizations and action potential bursts and was associated with increased frequency and amplitude of spontaneous excitatory postsynaptic currents and a reduced sIAHP. The
metabotropic glutamate receptor (mGluR) antagonist
(S)-
-methyl-4-carboxyphenylglycine did not modify synaptic activity
enhancement but did prevent sIAHP inhibition and
epileptiform discharges. The mGluR-dependent regulation of the
sIAHP was not caused by modulated intracellular
Ca2+ signaling. Histamine, isoproterenol, and
(±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid
reduced the sIAHP but did not increase synaptic activity and failed to evoke epileptiform activity. We conclude that 4AP or
4AP+Mg-free-induced enhancement of synaptic activity reduced the
sIAHP via activation of postsynaptic group I/II mGluRs. The increased excitability caused by the lack of negative feedback provided
by the sIAHP contributes to epileptiform activity, which requires the cooperative action of increased synaptic activity.
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