Intracarotid and Intravertebral Metrazol in Petit Mal Epilepsy

SINCE the demonstration that the three per second spike-and-wave complex seen in the electraencephalogram is almost pathognomonic of petit ma1 epilepsy,' many investigators have tried to discover its source. Because the petit ma1 pattern is bilaterally symmetrical in most cases a subcortical focus, possibly the thalamus, has been impl i~a ted .~ ,~ Metrazol ( pentamethylenetetrazol ) is closely bound to the petit ma1 pattern, and has been used extensively in animal experiments since it tends to induce repeated spikes and waves which simulate the petit ma1 complex. It is largely on the basis of these animal experiments that the thalamus has been considered to be the site of origin of petit ma1 discharges. In an effort to apply these observations to human patients with petit ma1 epilepsy, Spiegel and Wycis4 undertook studies with the stereoencephalotome using electrodes placed in the human thalamus but their results are not convincing. Clinically, Metrazol is frequently employed intravenously to precipitate seizures in epileptic patients, and those with petit ma1 epilepsy are exceedingly sensitive to the drug. Although this method of activation is very useful in establishing a diagnosis of epilepsy and in delineating foci of seizure activity, it fails to reveal the source of apparently generalized seizure discharges. The petit ma1 pattern appears to be one example of this type. The blood supply to the brain is partitioned in such a manner that the internal carotid artery supplies the ipsilateral cerebral cortex, putamen, caudate nucleus, and preoptic area of hypothalamus. The thalamus is excluded from this circulation, but is irrigated by the thalamogeniculate and thalamoperforating arteries derived from the posterior cerebral and posterior communicating arteries. The thalamus depends on the integrity of the posterior cerebral artery, and when the latter becomes occluded, softening of the thalamus occur^.^^^^^ Carotid arteriograms do not demonstrate the thalamic circulation,