Visuocortical epileptiform discharges in rabbits: differential effects on neuronal development in the lateral geniculate nucleus and superior colliculus.

We have studied the effects of interictal epileptiform discharges originating from the striate cortex on the development of the receptive field characteristics of neurons in the lateral geniculate nucleus (LGNd) and superior colliculus (SC) in neonatal rabbits. The paroxysmal discharges were generated by twice-daily injections of penicillin into an implanted cannula. Control injections of penicillin + penicillinase were given to the other striate cortex of the same animal. Similar experimental procedures were used to study the effect of such projected discharges on the LGNd neurons in adult rabbit. The results of the first experiment show that cortical epileptiform discharges, initiated in neonatal rabbits 7--9 days of age and continuing to 20--25 days of age, retard the normal development of LGNd cells. There was an abnormal increase of indefinite cells, cells failing to respond to any light stimulation, and a concurrent decrease of cells with concentric cells was still present in adult rabbits which had interictal discharges in the striate cortex limited to the period of 7--9 days to 21--25 days of age. The fourth experiment shows that the interictal discharges in neonatal rabbits do not affect the normal receptive field development of neurons in the SC. The present results demonstrate that asymptomatic interictal epileptiform discharges, produced without focal structural damages in immature brain, can affect the development of neuronal connectivity. These results may have some clinical implications in relation to our understanding about the learning and developmental disabilities exhibited in children who had episodic seizure discharges.