Functionally relevant and functionally disruptive (epileptic) synchronized oscillations in brain slices.
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.
Traub
R D
RD
Department of Neuroscience, University of Birmingham, United Kingdom.
Jefferys
J G
JG
Whittington
M A
MA
D000818:Animals; D001921:Brain / Q000503:physiopathology*; D004827:Epilepsy / Q000503:physiopathology*; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology; D009991:Oscillometry; D017966:Pyramidal Cells / Q000502:physiology; D013997:Time Factors