[Morphologic and histochemical changes in the secondary focus following cobalt-induced epileptogenic bioelectrical activity of the visual cortex in the adult rat]

Implantation of cobalt-agar rods into the visual cortex of 16 adult rats induced in some of the animals epileptiform bioelectrical activity and provoked in all of them histological and histochemical changes in the region of the implantation (primary focus) as well as in some ipsilateral projection sites of the visual cortex (secondary foci). The changes within the secondary foci are demonstrated in the Corpus geniculatum laterale, pars dorsale (dLGN), by means of 18 histochemical and 5 histological methods. Together with the appearance of hyperactive and degenerating neurones combined with neuronophagy and diminution of the number of synapses a marked gliosis developed, especially an increase of microglia. The destruction of the tissue induced a depression of energy and transmitter metabolism and intensified lytic processes. This is confirmed by the decreased activities of LDH, SDH, GPDH, G6PDH, NAD(P)H-TR, GABA-T and GDH and the increased activity of acid phosphatase in the neuropil of the secondary foci. Single hyperactive nerve and glial cells were accented by high activities of those enzymes which had a reduced activity in the neuropil. Since in our experiments agar-rods without cobalt never induced histological or histochemical changes in subcortical grisea of the visual system, the secondary foci seem to result from the direct influence of the cobalt, migrating in the corticothalamic projection pathway and identifiable in the dLGN by the TIMM technique.