[Threshold of penicillin induced epileptiform afterdischarge in brain slices of guinea pig].

Investigation of the regional threshold for epilepsy in many structures in the brain would contribute to the study of epileptogenesis. So we studied the threshold for epileptiform afterdischarge in the neocortex, hippocampus and cerebellar cortex using Na-Penicillin -G (Pc) of which epileptogenesis has been intensively investigated. In order to eliminate the influence from the outside of these structures, the brain slice method was utilized. Procedures for preparation of the tissue and incubation were about the same as those described by Yamamoto. In summary, after sacrifice, brain of the guinea pig was taken out and the hippocampus, neocortex and cerebellum were cut with a razor blade under a microscope. The thickness of the section was about 0.3 mm. Slices were incubated at 37 degrees C for about 30 min in the standard medium perfused with 95% O2 and 0% CO2. The chamber was continuously perfused with the standard medium which composed of NaCl, 124 mM, KCl, 5: KH2PO4, 1.24; MgSO4, 1.3; CaCl2, 2.4; NaHCO3, 26; and glucose, 10. Evoked potentials were elicited by electrical stimulation in the standard medium. Mossy fibers were stimulated and responses were recorded from the CA3 area in the hippocampus by glass pipette microelectrode. Subcortical white matter was stimulated and responses were recorded from the Purkinje cell layer in the cerebellum. Pc was added in the standard medium until epileptiform afterdischarges were superimposed on the evoked potentials. The results of this experiment demonstrated that each structure in the brain has a regional own threshold for Pc induced epileptiform afterdischarge.(ABSTRACT TRUNCATED AT 250 WORDS)