Functionally relevant and functionally disruptive (epileptic) synchronized oscillations in brain slices

Adv Neurol. 1999:79:709-24.

Abstract

Focal seizurelike events can be induced in experimental preparations by means of a number of distinct manipulations that differ in synaptic mechanisms. Nevertheless, the form of the seizurelike events can be explained with common principles, including long-lasting excitation of pyramidal cell dendrites and recurrent excitation between pyramidal cells that provides synchronization. One means of induction of seizurelike events, tetanic stimulation, induces a more physiologic type of activity before seizures are elicited, that is, gamma-frequency (> 20 Hz) oscillations. Such oscillations, called 40-Hz oscillations, are believed to be important for cognition in vivo. Experimental gamma oscillations depend critically on synaptic inhibition between interneurons, from interneurons to pyramidal cells, and on a tonic drive to pyramidal cells and interneurons by metabotropic glutamate receptors. The function of gamma oscillations appears to be imposition of a precise temporal structure on the firing patterns of pyramidal cells while still allowing the pyramidal cells to influence each other and be influenced by afferents selectively. We suggest that a relative loss of synaptic inhibition, occurring by any of a number of mechanisms, prevents the occurrence of gamma activity, allows recurrent pyramidal cell-pyramidal cell excitation to predominate, and thereby allows neuronal networks to generate functionally disruptive seizures.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Brain / physiopathology*
  • Epilepsy / physiopathology*
  • In Vitro Techniques
  • Interneurons / physiology
  • Oscillometry
  • Pyramidal Cells / physiology
  • Time Factors