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: 101/3/1588    most recent 90770.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map 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 Queiroz, C. M. Articles by Wadman, W. J. Search for Related Content PubMed PubMed Citation Articles by Queiroz, C. M. Articles by Wadman, W. J.

Dynamics of Evoked Local Field Potentials in the Hippocampus of Epileptic Rats With Spontaneous Seizures

¹Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, Amsterdam, The Netherlands; and ²Epilepsy Institutes of The Netherlands Foundation, Heemstede, The Netherlands

Submitted 15 July 2008; accepted in final form 1 October 2008

Abstract

A change in neuronal network excitability within the hippocampus is one of the hallmarks of temporal lobe epilepsy (TLE). In the dentate gyrus (DG), however, neuronal loss and mossy fiber sprouting are associated with enhanced inhibition rather than progressive hyperexcitability. The aim of this study was to investigate how alterations in excitability take place in association with spontaneous seizures expressed in the DG before, during, and after a seizure. For this purpose, we used freely moving rats that had developed spontaneous seizures after a kainate-induced status epilepticus (SE). Continuous EEG was recorded in the DG during several days along with local field potentials (LFPs) that were evoked every 15–30 s by applying paired-pulse stimuli to the angular bundle. Input-output relations showed increased paired pulse depression in epileptic compared with control rats, suggesting a rather strong inhibition in the DG during the interictal state. A characteristic pattern of changes in intrinsic excitability was observed during the ictal period: an increase in the population spike (PS) amplitude, mostly during the early phase of a seizure and often followed by a decrease of the main evoked potential amplitude. The paired-pulse extracellular postsynaptic potential (fEPSP) ratio increased during the seizure and did slowly recover to preictal levels after the seizure ended. Although clear changes in excitability occurred during and after seizure activity, changes of LFP parameters were more subtle before seizure onset; a significant reduction of LFP and PS amplitudes was observed that started 1–2 min in advance in 33% of the cases; in 18%, an increase of LFP/PS amplitude was observed; in the other cases, no significant change was observed. Taken together, these results provide evidence that, in this experimental model, DG physiology is more likely to follow the already ongoing seizure activity rather than to contribute to its generation.