Cobalt-induced epilepsy: an ultrastructural study

Metallic cobalt and aluminum rods were implanted into the cerebral cortices of rats. Almost all the animals with cobalt implantation were found to be epileptic 30 days after the operation. Tissue samples from the cerebral cortices were sampled for electron microscopy. The most significant changes in the cobalt-implanted animals were the disintegration of the rough endoplasmic reticulum in many cortical neurons and the accumulation of neurofilaments within the perikaryon. Such filamentous accumulation was usually found near the perinuclear position, at the periphery of the neurons, and in areas where there was a paucity of regular rough endoplasmic reticulum. Large aggregates of SER-like tubulovesicular structures were also found within many neuronal processes. Some of these neuronal processes could be identified to be postsynaptic dendritic terminals. Large nuclear pseudo-inclusions consisting of cytoplasmic materials were also found in some cortical neurons. These ultrastructural changes could also be occasionally observed in the opposite (cobalt-free) hemisphere of the brain (mirror image) in the cobalt-implanted animals. However, the brains of the aluminum-implanted or blank-control animals were free from any of these changes.