Neurophysiological mechanisms involved in grand mal seizures induced by metrazol and megimide

Abstract

Electro-clinical correlations during Metrazolor Megimide-induced grand mal seizures were studied in a series of fifty-seven cats. It was found that conventional EEG tracings suggest that earliest and maximal seiaure activity occurs in the cerebral cortex or thalamus, but photographs of the animals' behavior failed to show consistent relationships between any aspect of the conventional EEG and the onset of the behavioral convulsion. When the conventional EEG was eliminated by filters which attenuate activity below 1,000 c/sec, high frequency activity could be recorded from cortical and intracerebral structures. These recordings showed good relationships with the animals' behavior. Clinical myoclonic jerking was associated with large amplitude bursts of high frequency activity maximally in the brain-stem reticular formation. A generalized seizure occurred when the high voltage brain-stem reticular discharge became continuous rather than intermittent. The clonic phase of the generalized seizure was characterized by bursts of high frequency activity which gradually decreased in duration and amplitude toward the end of the seizure. In contrast to the conventional EEG, high frequency activity did not cease abruptly and simultaneously in all areas. The paralyzed and unanesthetized preparation showed less intense high frequency seizure activity than the freely moving animal, and the maximum of seizure activity was under these circumstances in the thalamus and cortex rather than the brain-stem. It is concluded that the recording of high frequency discharges adds a valuable dimension to electro-clinical correlations, and that the functional state of the animal may be an important variable in the amount and relative distribution of seizure activity.