Vulnerability to seizures induced by potassium dyshomeostasis in the hippocampus in aged rats

Abstract

Neurological diseases such as ischemia and dementia increase with aging, while whether seizure susceptibility increases with aging remains debatable. Seizure activity frequently originates in the hippocampus and is linked to excess of extracellular glutamate. To analyze seizure susceptibility in aged rats, the response of hippocampus excited excessively was evaluated based on extracellular concentrations of neurotransmitters and epileptic behavior. In 8-week-old and 90-100-week-old rats, which exhibited normal passive avoidance behavior, the hippocampuswas stimulated with 50-100 mM KCl using in vivo microdialysis. The basal concentrations of extracellular glutamate and γ-amino butyric acid (GABA) were almost the same between young and aged rats. The changes in their concentrations after stimulation with 50-100mM KCl were not also appreciably different between them. However, seizures, i.e., myoclonic jerks, were observed only in aged rats during the stimulation. These results suggest that aged rats are vulnerable to seizures induced by dyshomeostasis of potassium and chloride ions in the hippocampal extracellular fluid. Homeostasis of electrolytes in the hippocampal extracellular fluid seems to be important in preventing seizure activity in the elderly.