INITIATION OF ELECTROGRAPHIC LIMBIC SEIZURES BY NEURONAL NETWORKS IN ENTORHINAL AND PERIRHINAL CORTICES
Abstract number :
2.002
Submission category :
Year :
2002
Submission ID :
1860
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Philip de Guzman, Margherita D[ssquote]Antuono, Jean Gotman, Francois Dubeau, Massimo Avoli. Neurology & Neurosurgery, Montreal Neurological Institute/McGill University, Montreal, Quebec, Canada
RATIONALE: The hippocampus proper is often identified as a major player in mesial temporal lobe epilepsy. However, emerging clinical and experimental evidence indicates that parahippocampal territories, such as the perirhinal cortex (PC) and entorhinal cortex (EC), may contribute to seizure initiation and perhaps epileptogenesis. Since there is limited information regarding the involvement of different parahippocampal cortices in the initiation of limbic seizures, we addressed this issue by using horizontal rat brain slices containing both EC and PC along with the hippocampus.
METHODS: Three simultaneous field potential recordings were placed within the medial EC (ECm), lateral EC (ECl) and PC in slices superfused with the convulsant drug 4-aminopyridine (4AP, 50[mu]M).
RESULTS: The predominant pattern of epileptiform activity recorded in connected slices consisted of CA3-driven interictal discharges (duration=0.29[plusminus]0.01s; interval of occurrence= 0.3[plusminus]0.02Hz). Abating the propagation of this interictal pattern to EC and PC, by cutting the Schaffer collaterals, disclosed slow interictal (duration=0.47[plusminus]0.08s; interval=0.09[plusminus]0.01Hz) and ictal-like discharges (duration=30[plusminus]3.27s; interval=0.008[plusminus]0.001Hz); the latter was associated with NMDA receptor mechanisms. Simultaneous recordings performed in the ECm and ECl and in PC demonstrated bidirectional propagation of slow interictal and ictal discharges; time delay measurements from PC to ECl or from ECl to PC revealed delays of 11.2-50.4ms and 7.6[ndash]66.2ms, respectively. Interictal and ictal events most often initiated in the ECm and PC, respectively. Physical separation of the connections between the Ecm, ECl, and the PC, or functional inactivation of defined cortical areas by focal application of glutamatergic receptor antagonists resulted in independent epileptiform activity.
CONCLUSIONS: This evidence indicates that all parahippocampal networks analyzed in this study can generate epileptiform synchronization that sustains limbic seizures. Further, the results indicate the PC exhibits a preference for ictogenesis in vitro.
[Supported by: Canadian Institutes of Health Research and Epilepsy Canada.]