Изменение взаимодействий между астроцитарными отростками и синаптическими окончаниями при генерации эпилептиформной активности

Abstract

The aim of the present work was to compare the structural organization of excitatory synaptic contacts in intraocular septal transplants exhibiting normal and epileptiform activity. The work was performed on Wistar rats. The donor material for transplantation was the septal area of the brain isolated from 17-day-old rat fetuses. Three months after the grafting, the electrophysiological properties of neurotransplants were tested using short-term stimulation by single electrical impulses. According to the results of tests, the transplants were divided into two groups, with normal and epileptiform activity. A microscopic study of neurotransplants from both groups showed that nerve and glial cells, as well as the neuropil consisting of axons, dendrites, synaptic endings, and astrocytic processes were well differentiated. Axodendritic and axospinous synaptic endings were considered as three-part structural complexes (tripartite synapses), which included not only pre- and postsynaptic components, but also astrocytic processes surrounding them. Most of them had the morphological features of exciting contacts with strongly expressed postsynaptic densities whose size is a correlate of the efficiency of nervous transmission. A morphometric analysis of these synapses from functionally different types of transplants revealed no significant difference in the length of postsynaptic densities, as well as in the cross-section area and the perimeter of presynaptic boutons. At the same time, significant differences in the degree of the surrounding of synapses by astrocytic processes were found. In grafts characterized by epileptiform activity, the proportion of perisynaptic astrocytic processes was 1.8 times less than in the control ones. The data obtained indicate that perisynaptic astrocytic processes are the first to react to electrical stimulation and initiate the generation of epileptiform activity. It is assumed that the reduction of the astrocytic coverage of excitatory synapses facilitates the spread of neurotransmitters within extracellular spaces and the involvement of neighboring neurons in the synchronized neuronal activity.