Chronically isolated cerebral hemisphere in the cat: effects of parenteral administration of penicillin.

Brain electrical activity (EEG) of cats with chronic, complete, neural isolation of the cortex of an entire cerebral hemisphere was studied prior to and following intramuscular administration of penicillin (250,000--300,000 units/kg). The most prominent feature of the isolated hemisphere's EEG during base-line recordings was irregular, aperiodic, slow-wave activity with intermittent sharp waves and occasional spike discharges. Following penicillin administration there was an increase in the number of spikes and sharp waves in the isolated hemisphere and an increase in amplitude of the background activity. Simultaneously recorded EEG activity of the intact hemisphere demonstrated the paroxysmal burts of sharp waves or spike-wave complexes that have been described previously in normal animals. There was complete independence of the electrical activity recorded from intact and isolated hemispheres. These results indicate that intramuscularly administered penicillin can exert a convulsant effect on cortical structures in the absence of subcortical connections, but the generalized epileptiform activity seen in normal animals is dependent on thalamocortical connections.