Secondary epiliptogenesis in rats

Abstract

1. 1. Cobalt (powder and metallic slivers) was implanted in the posterior portion of one hemisphere of eight rats. These were acutely studied at various time intervals ranging from 6 to 32 days following the implantation procedure. 2. 2. Primary epileptiform spike activity, either spontaneous or induced by photic stimulation of hyperventilation, was observed in all of the rats except the 11-day and 32-day animals. Background activity and primary spike activity were more depressed at later time intervals. 3. 3. Good independent focal spike activity was present contralateral and homotopic to the primary focus in all rats examined after 8 days and, in most cases, the mirror focus was more active than the primary. 4. 4. Large lesions were observed in all rats but the size of the lesion did not correspond with the amount of primary electrical activity present. Inflammatory infiltrates were more diffuse in the powder-implanted rats and the craters produced by metallic slivers appeared to be more effectively walled off by fibroglial scar formation. 5. 5. “Dense” cells arranged in discrete nests were seen in the contralateral cortex of the experimental rats and these nests corresponded topographically to the borders of the primary lesion. 6. 6. The secondary epileptogenesis observed in rats appears similar to the “mirror focus” phenomenon described in other animals.