Journal of Neurophysiology, Vol 70, Issue 3 1018-1029, Copyright © 1993 by APS

ARTICLES

On the synchronous activity induced by 4-aminopyridine in the CA3 subfield of juvenile rat hippocampus

M. Avoli, C. Psarropoulou, V. Tancredi and Y. Fueta
Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.

1. Extracellular field potential and intracellular recordings were made in the CA3 subfield of hippocampal slices obtained from 10- to 24-day-old rats during perfusion with artificial cerebrospinal fluid (ACSF) containing the convulsant 4-aminopyridine (4-AP, 50 microM). 2. Three types of spontaneous, synchronous activity were recorded in the presence of 4-AP by employing extracellular microelectrodes positioned in the CA3 stratum (s.) radiatum: first, inter-ictal-like discharges that lasted 0.2-1.2 s and had an occurrence rate of 0.3-1.3 Hz; second, ictal-like events (duration: 3-40 s) that occurred at 4-38 x 10(-3) Hz; and third, large-amplitude (up to 8 mV) negative-going potentials that preceded the onset of the ictal-like events and thus appeared to initiate them. 3. None of these synchronous activities was consistently modified by addition of antagonists of the N-methyl-D-aspartate (NMDA) receptor to the ACSF. In contrast, the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 2-10 microM) reversibly blocked interictal- and ictallike discharges. The only synchronous, spontaneous activity recorded in this type of medium consisted of the negative-going potentials that were abolished by the GABAA receptor antagonists bicuculline methiodide (5-20 microM) or picrotoxin (50 microM). Hence they were mediated through the activation of the GABAA receptor. 4. Profile analysis of the 4-AP-induced synchronous activity revealed that the gamma-aminobutyric acid (GABA)-mediated field potential had maximal negative amplitude in s. lacunosum-moleculare, attained equipotentiality at the border between s. radiatum and s. pyramidale, and became positive-going in s. oriens. These findings indicated that the GABA-mediated field potential presumably represented a depolarization occurring in the dendrites of CA3 pyramidal cells. 5. This conclusion was supported by intracellular analysis of the 4-AP-induced activity. The GABA-mediated potential was reflected by a depolarization of the membrane of CA3 pyramidal cells that triggered a few variable-amplitude, fractionated spikes or fast action potentials. By contrast, the ictal-like discharge was associated with a prolonged depolarization during which repetitive bursts of action potentials occurred. Short-lasting depolarizations with bursts of action potentials occurred during each interictal-like discharge. 6. The GABA-mediated potential recorded intracellularly in the presence of CNQX consisted of a prolonged depolarization (up to 12 s) that was still capable of triggering a few fast action potentials and/or fractionated spikes.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				D. F. de Sevilla, J. Garduno, E. Galvan, and W. Buno Calcium-Activated Afterhyperpolarizations Regulate Synchronization and Timing of Epileptiform Bursts in Hippocampal CA3 Pyramidal Neurons J Neurophysiol, December 1, 2006; 96(6): 3028 - 3041. [Abstract] [Full Text] [PDF]

				F Manseau, M Danik, and S Williams A functional glutamatergic neurone network in the medial septum and diagonal band area J. Physiol., August 1, 2005; 566(3): 865 - 884. [Abstract] [Full Text] [PDF]

				M. Vreugdenhil, E. Bracci, and J. G. R. Jefferys Layer-specific pyramidal cell oscillations evoked by tetanic stimulation in the rat hippocampal area CA1 in vitro and in vivo J. Physiol., January 1, 2005; 562(1): 149 - 164. [Abstract] [Full Text] [PDF]

				M. D'Antuono, J. Louvel, R. Kohling, D. Mattia, A. Bernasconi, A. Olivier, B. Turak, A. Devaux, R. Pumain, and M. Avoli GABAA receptor-dependent synchronization leads to ictogenesis in the human dysplastic cortex Brain, July 1, 2004; 127(7): 1626 - 1640. [Abstract] [Full Text] [PDF]

				R. D. Traub, R. Bibbig, A. Piechotta, R. Draguhn, and D. Schmitz Synaptic and Nonsynaptic Contributions to Giant IPSPs and Ectopic Spikes Induced by 4-Aminopyridine in the Hippocampus In Vitro J Neurophysiol, March 1, 2001; 85(3): 1246 - 1256. [Abstract] [Full Text] [PDF]

				R. Motalli, J. Louvel, V. Tancredi, I. Kurcewicz, D. Wan-Chow-Wah, R. Pumain, and M. Avoli GABAB Receptor Activation Promotes Seizure Activity in the Juvenile Rat Hippocampus J Neurophysiol, August 1, 1999; 82(2): 638 - 647. [Abstract] [Full Text] [PDF]

				B. W. Strowbridge Glutamate Receptors Mediate TTX-Resistant Synchronous Activity in the Rat Hippocampus J. Neurosci., July 15, 1999; 19(14): 5758 - 5767. [Abstract] [Full Text] [PDF]

				P. Golshani and E. G. Jones Synchronized Paroxysmal Activity in the Developing Thalamocortical Network Mediated by Corticothalamic Projections and "Silent" Synapses J. Neurosci., April 15, 1999; 19(8): 2865 - 2875. [Abstract] [Full Text] [PDF]

				V. Tancredi, M. D'Antuono, A. Nehlig, and M. Avoli Modulation of Epileptiform Activity by Adenosine A1 Receptor-Mediated Mechanisms in the Juvenile Rat Hippocampus J. Pharmacol. Exp. Ther., September 1, 1998; 286(3): 1412 - 1419. [Abstract] [Full Text]

				V. Lopantsev and M. Avoli Participation of GABAA-Mediated Inhibition in Ictallike Discharges in the Rat Entorhinal Cortex J Neurophysiol, January 1, 1998; 79(1): 352 - 360. [Abstract] [Full Text] [PDF]

				M. Avoli, M. Barbarosie, A. Lucke, T. Nagao, V. Lopantsev, and R. Kohling Synchronous GABA-Mediated Potentials and Epileptiform Discharges in the Rat Limbic System In Vitro J. Neurosci., June 15, 1996; 16(12): 3912 - 3924. [Abstract] [Full Text] [PDF]