Effects of bilateral partial diencephalic lesions on cortical epileptic activity in generalized penicillin epilepsy in the cat

Abstract

The effects of bilateral symmetric partial diencephalic lesions on the epileptic discharges of generalized penicillin epilepsy in the cat were studied. Bilateral cooling of the inferior thalamic peduncle (ITP) reversibly abolished recruiting responses and epileptic discharges, whereas bilateral destructive lesions of the ITP were without effect. The effect of ITP cooling on these electrocortical phenomena is most likely due to inadvertent cooling of the nearby preoptic area. Preoptic cooling releases posterior hypothalamic and mesencephalic reticular mechanisms from inhibition and induces an electrocortical arousal response which is inimical to the elaboration of recruiting responses and of the epileptic bursts of generalized feline penicillin epilepsy. Of all other bilateral partial diencephalic lesions, only those of nucleus lateralis posterior exerted a pronounced effect on the epileptic discharges in this model. Even these lesions, however, rarely produced total abolition of the discharges, but reduced or modified them considerably. This may be related to the fact that the epileptic discharges in this model predominate in the cortical projection area of this nucleus. Bilateral lesions of Forel's fields had no effect on the epileptic discharges. We conclude that the thalamocortical volleys responsible for triggering the epileptic discharges of feline generalized penicillin epilepsy probably arise from multiple potential pacemakers which are widely distributed throughout the thalamus. It is, however, possible that the thalamocortical projection of the nucleus lateralis posterior, possibly through the “dorsal spindle system” of F. E. Horvath and P. Buser (1972, Brain Res. 39: 21–41), represents the principal, though not the exclusive, final common path through which the thalamocortical volleys precipitating the epileptic bursts in this model are mediated.