Journal of Neurophysiology, Vol 71, Issue 6 2463-2476, Copyright © 1994 by APS

ARTICLES

Multifocal spontaneous epileptic activity induced by restricted bicuculline ejection in the piriform cortex of the isolated guinea pig brain

M. De Curtis, G. Biella, M. Forti and F. Panzica
Department of Neurophysiology, Istituto Nazionale Neurologico, Milan, Italy.

1. We investigated the development of epileptic activity in the limbic lobe of the in vitro isolated brain preparation after induction of a restricted epileptic focus in the rostral portion of the anterior piriform cortex (APC) by means of local bicuculline ejection. 2. The modifications of the local responses evoked by stimulation of the lateral olfactory tract were consistent with an increase in excitability of layer II pyramidal neurons. The abnormal discharge output of the epileptic focus propagated throughout the piriform cortex (PC) and generated late synaptic stimulus-evoked epileptiform potentials in layer Ib, where corticocortical associative fibers contact the distal dendrites of pyramidal cells. 3. Spontaneous epileptiform potentials (SEPs) originated in the primary focus at the bicuculline ejection site 10-15 min after drug application and propagated via associative fibers to the posterior PC (PPC). 4. Autonomous secondary foci generating SEPs independently from the primary anterior focus developed in the PPC within 2 h after the bicuculline application. 5. Ictal events seldom occurred spontaneously in PC but could be induced by tetanic afferent stimulation. Evoked ictal events in PC had the characteristics of afterdischarges, being short in duration and localized in space and showing a progressively decreasing firing rate. 6. Self-sustained spontaneous ictal discharges were observed in the entorhinal cortex and hippocampus but not in PC after activation of the APC focus. 7. We conclude that in an acute pharmacological model of focal epilepsy, associative corticocortical connections hold a primary role 1) in the propagation of interictal epileptiform activity throughout the limbic lobe and 2) in the generation of secondary epileptic foci. We also demonstrate that self-sustained ictal events are not spontaneously generated in PC, although paroxysmal seizure-like discharges occur in hippocampus. We discuss the relevance of the rostral-to-caudal-directed associative fiber system in generation of limbic seizures.

This article has been cited by other articles:

				M. V. Sanchez-Vives, V. F. Descalzo, R. Reig, N. A. Figueroa, A. Compte, and R. Gallego Rhythmic Spontaneous Activity in the Piriform Cortex Cereb Cortex, May 1, 2008; 18(5): 1179 - 1192. [Abstract] [Full Text] [PDF]

				E. Labyt, L. Uva, M. de Curtis, and F. Wendling Realistic Modeling of Entorhinal Cortex Field Potentials and Interpretation of Epileptic Activity in the Guinea Pig Isolated Brain Preparation J Neurophysiol, July 1, 2006; 96(1): 363 - 377. [Abstract] [Full Text] [PDF]

				V. Gnatkovsky and M. de Curtis Hippocampus-Mediated Activation of Superficial and Deep Layer Neurons in the Medial Entorhinal Cortex of the Isolated Guinea Pig Brain J. Neurosci., January 18, 2006; 26(3): 873 - 881. [Abstract] [Full Text] [PDF]

				R. Demir, L. B. Haberly, and M. B. Jackson Epileptiform Discharges With In-Vivo-Like Features in Slices of Rat Piriform Cortex With Longitudinal Association Fibers J Neurophysiol, November 1, 2001; 86(5): 2445 - 2460. [Abstract] [Full Text] [PDF]

				G. Biella, L. Uva, and M. de Curtis Network Activity Evoked by Neocortical Stimulation in Area 36 of the Guinea Pig Perirhinal Cortex J Neurophysiol, July 1, 2001; 86(1): 164 - 172. [Abstract] [Full Text] [PDF]

				G. Biella and M. de Curtis Olfactory Inputs Activate the Medial Entorhinal Cortex Via the Hippocampus J Neurophysiol, April 1, 2000; 83(4): 1924 - 1931. [Abstract] [Full Text] [PDF]

				S. van der Linden, F. Panzica, and M. de Curtis Carbachol Induces Fast Oscillations in the Medial but not in the Lateral Entorhinal Cortex of the Isolated Guinea Pig Brain J Neurophysiol, November 1, 1999; 82(5): 2441 - 2450. [Abstract] [Full Text] [PDF]

				Y. Tsau, L. Guan, and J.-Y. Wu Epileptiform Activity Can Be Initiated in Various Neocortical Layers: An Optical Imaging Study J Neurophysiol, October 1, 1999; 82(4): 1965 - 1973. [Abstract] [Full Text] [PDF]

				M. de Curtis, A. Manfridi, and G. Biella Activity-Dependent pH Shifts and Periodic Recurrence of Spontaneous Interictal Spikes in a Model of Focal Epileptogenesis J. Neurosci., September 15, 1998; 18(18): 7543 - 7551. [Abstract] [Full Text] [PDF]