Epileptogenesis Following Neocortical Trauma From Two Sources of Disinhibition

J Neurophysiol. 1997 Nov;78(5):2804-10. doi: 10.1152/jn.1997.78.5.2804.

Abstract

Epileptogenesis following neocortical trauma from two sources of disinhibition. J. Neurophysiol. 78: 2804-2810, 1997. Intracellular and field potential recordings were obtained from superficial and deep neurons from both intact coronal rat somatosensory slices, and from slices which had been acutely divided into a superficial strip of cortex ( approximately 450 micron from the pia) and a deep segment. Membrane properties for cells in the traumatized slices were similar to those of their counterparts in intact slices. However, synaptic hyperexcitability developed in the deep segments in which a majority of cells likely underwent dendrotomy. This hyperexcitability was manifested by epileptiform activity in 54% of traumatized slices. Measurements of fastGABAergic inhibitory strength showed these slices were disinhibited. Superficial delivery of tetrodotoxin to the upper 450 micron of intact slices led to disinhibition of fast GABAergic transmission as well as an attendant increase in excitatory postsynaptic potential strength but not epileptogenesis. Pharmacological maneuvers aimed at preventing glutamate-triggered increases in intracellular calcium [glutamate ionotropic antagonists, dantrolene, and bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid (BAPTA)-AM] showed that a 1 h treatment in these agents conferred protection against epileptogenesis. These results demonstrate that the seizure-like activity developing in deep dendrotomized cortical segments resulted from two sources of GABAergic disinhibition: the physical removal of important superficial inhibitory circuits and glutamate-triggered increases in intracellular calcium.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 6-Cyano-7-nitroquinoxaline-2,3-dione / pharmacology
  • Animals
  • Calcium / metabolism
  • Cell Membrane / drug effects
  • Cell Membrane / physiology
  • Chelating Agents / pharmacology
  • Dantrolene / pharmacology
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / pharmacology
  • Epilepsy / physiopathology*
  • Excitatory Amino Acid Antagonists / pharmacology
  • Excitatory Postsynaptic Potentials / drug effects
  • Excitatory Postsynaptic Potentials / physiology*
  • In Vitro Techniques
  • Models, Neurological
  • Neocortex / drug effects
  • Neocortex / physiology*
  • Neocortex / physiopathology
  • Neurons / drug effects
  • Neurons / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Somatosensory Cortex / drug effects
  • Somatosensory Cortex / physiology*
  • Somatosensory Cortex / physiopathology
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*
  • Virulence Factors, Bordetella / pharmacology
  • gamma-Aminobutyric Acid / physiology

Substances

  • Chelating Agents
  • Excitatory Amino Acid Antagonists
  • Virulence Factors, Bordetella
  • 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
  • Egtazic Acid
  • gamma-Aminobutyric Acid
  • 6-Cyano-7-nitroquinoxaline-2,3-dione
  • Dantrolene
  • Calcium