Fifty-two male albino rats aged 7, 9, 12 and 18 days and adult, immobilized with d-turbocurarine, were studied. Discharges were triggered from a penicillin focus with electrical pulses of double the threshold intensity needed to evoke an interhemispheric response (IHR). Developmental changes in the IHR and in spontaneous interictal discharges did not differ from the results described in earlier studies. Practically no discharges could be triggered in 7-day old animals (only a few at a very low stimulation frequency). In the other age groups, discharges were triggered at two optimal frequencies, of which the lower one rose from 0.1 to 0.6 c/s during development, while the higher one was relatively stable (about 1 c/s). With higher frequency triggering, marked signs of fatigue of the focus (intermittent triggering, loss of the main negative wave) appeared, especially in young animals. The averaged shape of triggered discharges was similar in 9- and 12-day-old rats. It consisted of a first IHR positivity which triggered the first positive wave of the focal discharge, followed by a high negative wave. In the 18-day-old and adult group, both initial positive waves merged to form a single wave. The duration of the individual waves of the triggered discharge was not significantly shorter than the duration of the corresponding waves of spontaneous discharge.

Epilepsy Research in the Institute of Physiology of the Czech Academy of Sciences in Prague