Chronic low-dose maternal exposure to methylmercury enhances epileptogenicity in developing rats

Effects of continuous low-dose maternal methylmercury intoxication on the induction and propagation of ictal epileptiform activity induced by 3-aminopyridine, were investigated on the neocortex of 4-weeks-old offspring rats. Epileptogenicity was significantly increased in offspring of mercury-treated animals compared to those of controls, characterized by more frequent occurrence of periodic ictal activity, a facilitated propagation of epileptiform discharges and a strong tendency to generalization. The latency of first ictal event was slightly shorter and the average duration of individual ictal periods slightly longer in treated animals. However, the amplitude of seizure discharges was significantly smaller in treated animals than in controls. We conclude, that the synaptic and membrane mechanisms responsible for initiation and propagation of paroxysmal activity were probably facilitated, while the efficacy of cortical inhibition, in preventing initiation and spread of epileptiform discharges was reduced by mercury treatment in the developing nervous system. The smaller amplitude of paroxysmal discharges could be a sign of a remarkable loss of cortical neurons.