Stimulation of substantia nigra pars reticulata suppresses neocortical seizures

The effects of unilateral electrical stimulation of the substantia nigra pars reticulata (SNpr) on the electrocorticographic (ECoG) manifestations of seizures were studied in anesthetized rats. Epileptiform activity was provoked in the primary focus (Pf) by unilateral, local application of 3-aminopyridine which induced secondary focus in the homologous area of the contralateral cortex (mirror focus, Mf). The position of the electrode for stimulation of SNpr was contralateral to the Pf. The results showed a strong suppressive nigral effect on cortical seizure propagation and on seizure susceptibility in both hemispheres. Stimulation of the SNpr prevented the manifestation of sustained epileptiform events, decreased the rate of seizure appearance in the Mf, delayed the onset of paroxysmal activity and markedly reduced the amplitude and duration of ictal episodes at both foci. Seizure potentials of lower frequencies disappeared, while the relative proportion of those of higher frequency increased in SNpr-stimulated animals. SNpr stimulation had no significant effect on fully developed seizures. Our observations support the idea that SNpr might be involved in the control of cortical seizure susceptibility, regulating other structures which are possibly involved in the generation and propagation of seizure.