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This Article Full Text Full Text (PDF) All Versions of this Article: 571/2/461    most recent jphysiol.2005.100925v1 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by Polack, P.-O. Articles by Charpier, S. Search for Related Content PubMed PubMed Citation Articles by Polack, P.-O. Articles by Charpier, S. Related Collections Integrative

¹ Institut National de la Santé et de la Recherche Médicale U667, Collège de France, Paris F-75231 and Université Pierre et Marie Curie, Paris F-75005, France

Spontaneous high-voltage rhythmic spike (HVRS) discharges at 6–12 Hz have been widely described in the electrocorticogram (EcoG) of Long-Evans rats. These ECoG oscillations have been proposed to reflect a state of attentive immobility allowing the optimization of sensory integration within the corticothalamic pathway. This hypothesis has been challenged by recent studies emphasizing similarities between HVRS discharges and spike-and-wave discharges (SWDs) in well-established rat genetic models of absence epilepsy. Here, we made in vivo intracellular recordings to determine, for the first time, the cellular mechanisms responsible for the synchronized oscillations in the corticothalamic loop during HVRS discharges in the Long-Evans rats. We show that HVRS discharges are associated in corticothalamic neurones with rhythmic suprathreshold synaptic depolarizations superimposed on a tonic hyperpolarization, likely due to a process of synaptic disfacilitation. Simultaneously, thalamocortical neurones exhibit a large-amplitude ‘croissant’-shaped membrane hyperpolarization with a voltage sensitivity suggesting a potassium-dependent mechanism. This thalamic hyperpolarizing envelope was associated with a membrane oscillation resulting from interactions between excitatory synaptic inputs, a chloride-dependent inhibitory conductance and voltage-gated intrinsic currents. These cortical and thalamic cellular mechanisms underlying HVRS activity in Long-Evans rats are remarkably similar to those previously described in the thalamocortical networks during SWDs. Thus, the present study provides an additional support to the hypothesis that HVRS activity in Long-Evans rats is an absence-like seizure activity.

(Received 28 October 2005; accepted after revision 5 January 2006; first published online 12 January 2006)
Corresponding author S. Charpier: Institut National de la Santé et de la Recherche Médicale U667, Collège de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France. Email: stephane.charpier{at}college-de-france.fr

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				F.-Z. Shaw 7-12 Hz High-Voltage Rhythmic Spike Discharges in Rats Evaluated by Antiepileptic Drugs and Flicker Stimulation J Neurophysiol, January 1, 2007; 97(1): 238 - 247. [Abstract] [Full Text] [PDF]