Interictal EEG pattern in rabbit penicillin epilepsy

The effects of Na-penicillin G (1,000,000 I.U./kg i.v.) were studied in 28 rabbits implanted with surface and deep electrodes in the medial (mT) and lateral (lT) nuclei of the thalamus and in the cornu Ammonis dorsalis (CAd). Attention was focused on interictal spike activity, cortical spindle activity and spikes-spindles relationship. A multifocal interictal EEG pattern, represented by cortical and thalamic spikes, was observed in 20 animals. A clear association between cortical spikes and spindles occurred almost constantly. Moreover a statistically significant increase in the average duration of spindles without changes in the average frequency was noticed. Seizure discharges had always a focal start and secondary generalization. The EEG features of parenteral penicillin epilepsy in the rabbit appeared to be more similar to those of the rat than to those of the cat. The spindle activity changes and the paroxysmal spike activity can be interpreted as two independent penicillin induced features appearing during raised cortical excitability periods.