Kindling induced changes in EEG recorded during stimulation from the site of stimulation: collapse of GABA-mediated inhibition and onset of rhythmic synchronous burst.

As a new approach to the functional alteration of kindled epileptogenic foci, we have demonstrated electroencephalographic (EEG) changes at the site of stimulation at the times when the kindling stimulation is applied in freely moving rats. In the kindled amygdala, three components of response were observed: an initial evoked potential, a subsequent EEG suppression, and an eventual burst of rhythmic spiking. The three components were a common feature also in the kindled hippocampus and prepyriform region. The duration of component 2, EEG suppression, progressively increased with each day of kindling (40 to 50 days), but dramatically shortened again after a rest period of 1 month. It was sensitive to pharmacological manipulations of gamma-aminobutyric acid (GABA). The amplitude of component 3, rhythmic spiking, increased during kindling, and was relatively insensitive to current intensities. The increased amplitude was long-lasting, independent of GABAergic, monoaminergic, and cholinergic manipulations, but sensitive to a benzodiazepine. It is suggested that component 3 is the outbreak of synchronous excitatory action which may be related to the basic mechanism of kindling.