[Dynamics of synaptic changes in experimental audiogenic epilepsy].

Abstract

The dynamics of ultrastructural changes in axonal endings were studied after experimental epileptic seizures. Mice and rats from strains with genetically--determined audiogenic epilepsy were used as a model of epilepsy. The animals were divided into 3 groups: in group 1 only one seizure was evoked, in group 2 eight seizures within 4 hours, group 3 served as control. The animals were killed immediately after the last seizure, 30 min. after it or 1 hour after the seizure. Hippocampal gyrus cortex was impregnated with zinc-iodide-osmium tetroxide and synapses were examined under electron microscope. The number of synaptic vesicles showing positive reaction with zinc iodide was calculated in 20 synaptic boutons in each group. A significant correlation was demonstrated between the frequency of seizures and the survival time after the seizure on the one hand, and synaptic changes, on the other. In the control group 97% of synaptic vesicles were filled with neurotransmitter substance giving positive reaction with zinc iodide. Immediately after the single seizure 46% of synaptic vesicles were found emptied, 30 min. later the neurotransmitter substance was demonstrated in 79% of vesicles, 1 hour later 82% of vesicles had normal appearance. Immediately after serial seizures 91% of vesicles were found empty, 30 min. later the neurotransmitter was present in 50% of vesicles, 1 hour later in 78%. In another group of animals seizures were evoked once daily for 40 days (chronic epilepsy model). Synaptic changes were different: the synaptic boutons were swollen, the number of vesicles was reduced, greatly enlarged vesicles and clear membrane-bound vacuoles appeared. They evidenced degenerative character of changes. It is suggested that degenerative synaptic changes may be a substrate of epileptic dementia.