An ontogenic study of amygdala seizures induced by penicillin in rats.

Amygdaloid seizures were induced by unilateral injection of penicillin into the amygdala in infant and young rats to investigate the ontogenic development of the amygdaloid seizure. "Repetitive isolated discharges" and "sustained high-frequency discharges" appeared in 3- to 4-day-old rats. In these rats, the repetitive discharges appeared in bilateral subcortical structures simultaneously with those of the amygdaloid penicillin focus, but sustained high-frequency discharges were localized to the ipsilateral subcortical structures. In 9- to 10-day-old and 14- to 15-day-old rats, repetitive discharges occurred simultaneously in the bilateral cortices and subcortical structures. In contrast to them, sustained high-frequency discharges propagated faster from the amygdala penicillin focus to the bilateral midbrain reticular formation and medial nucleus of the thalamus than to other regions. In 20- to 21-day-old and older rats, both events occurred simultaneously at all cerebral sites. These results indicate that the subcortical structures, especially the midbrain reticular formation and medial nucleus of the thalamus, play an important role in seizure propagation from the ipsilateral to the contralateral hemisphere in infant rats.