Journal of Neurophysiology, Vol 58, Issue 5 1052-1065, Copyright © 1987 by APS

ARTICLES

Spontaneous ictal-like discharges and sustained potential shifts in the developing rat neocortex

J. J. Hablitz
Department of Neurology, Baylor College of Medicine, Houston, Texas 77030.

1. Intra- and extracellular recording techniques were used to study epileptogenesis in in vitro slices of immature rat neocortex. Slices of sensorimotor cortex were prepared from animals 5-60 days old. Epileptiform activity was induced by bath application of 50 microM picrotoxin. 2. Convulsant-induced paroxysmal activity was observed only rarely in the youngest age group (5-7 days) and consisted of orthodromically evoked bursts of low-amplitude isolated discharges. This activity was labile and could be evoked only at long interstimulus intervals (greater than 10 s). 3. Extracellular recordings in slices from 8- to 15-day-old rats showed spontaneous epileptiform activity consisting of 10- to 30-s paroxysms of repetitive spike discharges superimposed on a 3- to 5-mV negative steady potential. This steady potential declined slightly during the course of the prolonged discharge and returned quickly to base line following the last spike discharge. 4. Laminar analysis of epileptiform activity in 8- to 15-day-old rats showed that the spike discharges were negative and superimposed on a positive slow wave in superficial cortical layers. At 100 micron below the pial surface, the slow potential reversed polarity and remained negative throughout the remainder of the cortex. Spike discharges reversed polarity 800 micron below the pial surface. 5. In intracellular recordings from slices obtained from 9- to 14-day-old animals, each paroxysm began with a sharply rising membrane depolarization (paroxysmal depolarizing shift, or PDS). A second PDS occurred before the cells repolarized to their resting potential. A series of PDSs then followed, superimposed on a sustained membrane depolarization. This was associated with a 33% decrease in input resistance. Afterhyperpolarizations (AHPs) following termination of the depolarization were low in amplitude or absent. 6. In the 16- to 30-day-old age group, extracellular recordings showed paroxysmal activity consisting of 3-10 initial spikes followed by a sustained, slow, negative-potential shift. This slow potential could be as great as 30 mV in amplitude and could last as long as 180 s. Paroxysmal events recurred spontaneously at intervals of 4-11 min. Spontaneous PDSs and slow, negative-potential shifts were not observed after 30 days of age, although PDSs could still be evoked by orthodromic stimulation. 7. Intracellular recordings in the 16- to 30-day-old group revealed that each paroxysmal event consisted of an initial period of increased synaptic activity and cellular firing, followed by a marked, long-lasting depolarization (LLD), culminating in an AHP.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				Y. Schiller and Y. Bankirer Cellular Mechanisms Underlying Antiepileptic Effects of Low- and High-Frequency Electrical Stimulation in Acute Epilepsy in Neocortical Brain Slices In Vitro J Neurophysiol, March 1, 2007; 97(3): 1887 - 1902. [Abstract] [Full Text] [PDF]

				D. J. Pinto, S. L. Patrick, W. C. Huang, and B. W. Connors Initiation, Propagation, and Termination of Epileptiform Activity in Rodent Neocortex In Vitro Involve Distinct Mechanisms J. Neurosci., September 7, 2005; 25(36): 8131 - 8140. [Abstract] [Full Text] [PDF]

				K. Y. Tseng and P. O'Donnell Post-pubertal Emergence of Prefrontal Cortical Up States Induced by D1-NMDA Co-activation Cereb Cortex, January 1, 2005; 15(1): 49 - 57. [Abstract] [Full Text] [PDF]

				Y. Schiller Activation of a Calcium-Activated Cation Current During Epileptiform Discharges and Its Possible Role in Sustaining Seizure-Like Events in Neocortical Slices J Neurophysiol, August 1, 2004; 92(2): 862 - 872. [Abstract] [Full Text] [PDF]

				W. van Drongelen, H. Koch, C. Marcuccilli, F. Pena, and J.-M. Ramirez Synchrony Levels During Evoked Seizure-Like Bursts in Mouse Neocortical Slices J Neurophysiol, September 1, 2003; 90(3): 1571 - 1580. [Abstract] [Full Text] [PDF]

				T. A. Simeone, S. D. Donevan, and J. M. Rho Molecular Biology and Ontogeny of {gamma}-Aminobutyric Acid (GABA) Receptors in the Mammalian Central Nervous System J Child Neurol, January 1, 2003; 18(1): 39 - 48. [Abstract] [PDF]

				Y. Schiller Inter-Ictal- and Ictal-Like Epileptic Discharges in the Dendritic Tree of Neocortical Pyramidal Neurons J Neurophysiol, December 1, 2002; 88(6): 2954 - 2962. [Abstract] [Full Text] [PDF]

				T. Shimizu, T. Maehara, T. Hino, T. Komori, H. Shimizu, A. Yagishita, T. Yokota, S. Hirai, and P. M. Rossini Effect of multiple subpial transection on motor cortical excitability in cortical dysgenesis Brain, July 1, 2001; 124(7): 1336 - 1349. [Abstract] [Full Text] [PDF]

				M. A. Castro-Alamancos Origin of Synchronized Oscillations Induced by Neocortical Disinhibition In Vivo J. Neurosci., December 15, 2000; 20(24): 9195 - 9206. [Abstract] [Full Text] [PDF]

				J. E. Wells, J. T. Porter, and A. Agmon GABAergic Inhibition Suppresses Paroxysmal Network Activity in the Neonatal Rodent Hippocampus and Neocortex J. Neurosci., December 1, 2000; 20(23): 8822 - 8830. [Abstract] [Full Text] [PDF]

				R. Kohling, M. Vreugdenhil, E. Bracci, and J. G. R. Jefferys Ictal Epileptiform Activity Is Facilitated by Hippocampal GABAA Receptor-Mediated Oscillations J. Neurosci., September 15, 2000; 20(18): 6820 - 6829. [Abstract] [Full Text] [PDF]

				F. Amzica and D. Neckelmann Membrane Capacitance of Cortical Neurons and Glia During Sleep Oscillations and Spike-Wave Seizures J Neurophysiol, November 1, 1999; 82(5): 2731 - 2746. [Abstract] [Full Text] [PDF]

				K. M. Jacobs, B. J. Hwang, and D. A. Prince Focal Epileptogenesis in a Rat Model of Polymicrogyria J Neurophysiol, January 1, 1999; 81(1): 159 - 173. [Abstract] [Full Text] [PDF]

				A. N. van den Pol, X.-B. Gao, P. R. Patrylo, P. K. Ghosh, and K. Obrietan Glutamate Inhibits GABA Excitatory Activity in Developing Neurons J. Neurosci., December 15, 1998; 18(24): 10749 - 10761. [Abstract] [Full Text] [PDF]