Alterations in cholinergic enzymes during the development of cobalt-induced epilepsy in the rat

Choline acetyltransferase and cholinesterase activities were established in cerebral cortical tissue from rats rendered epileptic by the administration of cobalt-gelatin slivers to the cortex. Cobalt-treated rats exhibited a significant reduction of the pentylenetetrazol seizure threshold 4 days after cobalt implantation. This effect persisted up to 7 weeks. Enzyme activity was determined in cortical tissue adjacent to the site of cobalt implantation and in the homotropic area of the contralateral hemisphere. Choline acetyltransferase activity in the primary area declined markedly the first week after cobalt implantation, but by 21 days, when the seizure threshold was still depressed, activity had increased significantly above control. Cholinesterase activity decreased significantly the first week and by 3 weeks had returned to control levels. Although not significant, activities of both enzymes in the contralateral cortex, tended to parallel those in primary cortex. The initial decline in enzymatic activity coincided with the development of epileptogenic activity in the rats. The subsequent return to control or higher levels of activity was, however, not accompanied by any further change in pentylenetetrazol seizure thresholds.