Objective: To find morphological changes of synapses related to the spike discharge by observation on ultrastructures of the EEG spike foci of cerebral cortexes.
Material and methods: The cerebral cortexes were obtained surgically from the EEG spike (recorded by flaky silver electrodes on the surface of cortexes) foci and nonspike areas within the limits of the brain tissue that would be removed in 20 cases of human epilepsy, and were processed for transmission electron microscopic (TEM) observation.
Results: In the spike foci, presynaptic terminals of axospinal asymmetric synapses were obviously swollen but postsynaptic spines were relatively unaffected. In these synapses, the synaptic vesicles remarkably decreased in number and accumulated predominantly at the presynaptic membranes or aggregated. Similar changes were observed in the presynaptic terminals of the axospinal asymmetric synapses in the nonspike areas but were of milder degree than in the spike foci.
Conclusion: Axospinal asymmetric synapses may release a large quantity of excitatory neurotransmitters, which may result in epileptic abnormal electric activities during seizure.