Histochemical study of cobalt-induced focal epilepsy.

A previous study showed a strong relationship between human focal epilepsy and the presence in the cortex of "activated" astrocytes characterized by an intense activity of dehydrogenases (DH) involved in glucose metabolism and of glutamate DH. Using the semi-chronic model of cobalt-induced experimental focal epilepsy in the rat, we investigated a possible correlation between astrocyte modifications and the chronological development of the epileptic manifestations on the ECoG. After a few days the cobalt-implanted rats present spikes, then sharp waves followed by an electrical crisis and ultimately motor seizures. Activated astrocytes were found in each phase of this evolution. Their number increases with the intensity of the manifestations. There is a close relationship between activated astrocytes and focal epileptic phenomena. At this stage of our study it is clear that the presence of activated astrocytes is not a consequence of seizures. However, it is impossible to say whether the activation is secondary to the hyperactivity of the neurons or directly responsible for the constitution of the epileptic focus. In any case, activated astrocytes provide a new means of localizing an epileptogenic focus.