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Adv Neurol. 1999;79:709-24.

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

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1
Department of Neuroscience, University of Birmingham, United Kingdom.

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.

PMID:
10514857
[Indexed for MEDLINE]
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