Ultrastructure of hippocampal field CA1 in rats after status epilepticus induced by systemic administration of kainic acid.

The ultrastructure of hippocampal field CA1 in rats was studied 14 days after status epilepticus induced by administration of kainic acid. Structural changes were seen in 40% of cells, predominantly interneurons, which showed both reversible changes (mitochondria with an electron-dense matrix or small numbers of short cristae, moderate dilation of rough endoplasmic reticulum (RER) cisterns, and small numbers of ribosomes) and more significant abnormalities: swollen mitochondria with very small numbers of cristae, which were partially degraded, some with damaged mitochondrial membranes, along with pathologically damaged RER components and focal or peripheral chromatolysis. Chromatolyzed areas sometimes contained membrane-like includes and vacuoles. In addition, the neuropil contained occasional large osmiophilic formations surrounded by astrocyte processes with accumulations of glycogen or gliofibrils. Synaptoarchitectonics were also altered. Asymmetrical synapses were often seen on small dendrites and spines, with highly osmiophilic postsynaptic zones, their synaptic terminals containing numerous synaptic vesicles and large vesicles with electron-dense cores. Some presynaptic endings showed clear signs of classical dark-type degeneration. As the nucleus remained intact in all types of altered neurons, it appears that most cells underwent pathological changes of the necrotic type.