EXPERIMENTAL SUBCORTICAL EPILEPTIFORM FOCUS.

SUMMARY A method is described for creating lesions in subcortical nuclear structures of cats. With small amounts of granular aluminum oxide, a primary focus “discharging” into the hippocampus can be localized. Discrete epileptogenic lesions in deep structures can be associated with development of secondary discharges at sites in the opposite hemisphere. Continuous epileptiform bombardment in networks produces synaptic or cellular changes which are evidenced by the secondary epileptic focus in the contralateral hippocampus. These changes can be recorded in other structures connected to the hippocampus, such as the amygdaloid nucleus, septal region and tegmentum mesencephali. We postulate that the secondary discharges are accompanied by a neurohumoral mechanism at the synaptic level. This mechanism is altered by the continuous epileptiform bombardment emanating from the epileptogenic primary focus. We attribute the changes from normal to abnormal epileptiform activity in the cell to metabolic alteration of the cell. Sectioning of the anterior commissure, fornix and corpus callosum before injection of alumina into the hippocampus prevented development of the secondary discharges. Sectioning after development of secondary discharges did not modify the epileptogenic discharges in the opposite hemisphere. Total isolation of the side with the lesion after development of discharges in the secondary focus did not produce significant change in the mirror focus. Intraperitoneal or intramuscular injection of phenobarbital prevented or decreased the spread of epileptiform hippocampal discharges. Intracerebral administration of this drug into the primary epileptiform focus had no notable effect, but administration into the site of the secondary focus exerted a slightly inhibitory action on the secondary focus and a suppressive effect on the further spread of epileptiform discharges. In contrast, intracerebral administration of dilantin produced a blockade of primary as well as secondary epileptiform discharges. On the other hand, intraperitoneal or intramuscular dilantin had inhibitory or facilitatory effects, depending on dosages of the drug. RESUME Description d'une methode pour l'obtention de lesions dans les structures nucleaires sous-corticales des chats; on peut, avec de petites quantites d'oxyde d'aluminium granulaire, provoquer des decharges primaires dans l'hippocampe d'un cote et des decharges secondaires dans l'hippocampe contralateral et dans d'autres structures reliees a l'hippocampe, telles que le noyau amygdaloide, la region septale et la calotte du mesencephale. Nous supposons que les decharges secondaires sont accompagnees d'un mecanisme neurohumoral au niveau synaptique; mecanisme qui serait altere par le bombardement epileptiforme continu emanant du foyer epileptogene primaire. Nous attribuons les changements de l'activite normale en activite anormale a une alteration metabolique de la cellule. Une section de la commissure anterieure, du fornix et du corps calleux faite avant l'injection d'aluminium dans l'hippocampe previent le developpement des decharges secondaires. Une section faite apres le developpement des decharges secondaires ou l'isolement total du cote ou se trouve la lesion, ne produit aucun changement significatif dans le foyer “en miroir”. Des injections intraperitoneales ou intramusculaires de phenobarbital ont prevenu ou diminue l'extension des decharges epileptiformes hippocampales. L'administration intracerebrale de cette substance dans le foyer epileptiforme primaire n'a pas eu d'effet notable mais son administration du cote du foyer secondaire a exerce une action legerement inhibitrice sur les decharges secondaires et un effet suppressif sur une eventuelle extension des decharges epileptiformes. En contraste avec ce qui precede, une administration intracerebrale de diphenylhy-dantoine a produit un blocage des decharges epileptiformes, primaires aussi bien que secondaires. Par contre, la diphenylhydantoine en administration intraperitoneale ou intramusculaire, a montre un effet facilitateur ou inhibiteur sur les decharges selon le dosage de la substance.