The effects of bilateral ventral hippocampal lesions on amygdaloid kindling in cats

The clinical relevance of Ammon's horn sclerosis in epilepsy has not been fully ellucidated. This study was designed to examine the effects of bilateral ventral hippocampal lesions (Ammon's horn + dentate gyrus) on the minimal electroconvulsive threshold (ECT) intensity, kindling rates and transference phenomenon in cats kindled from the amygdala (AM). Ten adult cats were used. In the first experiment, lesions were made electrolytically in the bilateral hippocampi after completion of the primary site (PS) kindling from the left AM. Subsequently, the right AM (secondary site: SS) was kindled. In the second experiment, the hippocampal lesion was made prior to the PS-kindling which was followed by the SS-kindling. In the first experiment, the ECT intensity was unchanged by the hippocampal lesions after PS-kindling. The seizure pattern and EEG pattern in the generalized convultion were changed to show an asymmetrical, asynchronous pattern by the lesions. Facilitation of SS-kindling following the PS-kindling (positive transfer) was diminished by the lesions. In the second experiment, the formation of hippocampal lesions prior to the kindling retarded the PS kindling rates slightly. The seizure pattern and EEG pattern of the generalized convulsion was asymmetrical and asynchronous. In addition, positive transfer from PS to SS was blocked by the lesions. These results indicate that the ventral hippocampal formation and hippocampal commissure may be critical brain sites for the establishment of the transference phenomenon that reflects secondary epileptogenic changes in the brain