Amygdala-kindled postictal inhibition: Effect of intertrial intervals on repeated days

Fully amygdala-kindled rats with stable afterdischarge durations and seizure ranks of five were evaluated with suprathreshold stimulations (400 μA) at variable interstimulus intervals. Subjects were stimulated either once a day or four times a day at one of five interstimulus intervals (5, 15, 30, 60, or 180 min) for 5 days. All subjects were tested under each of the six paradigms. Profound inhibition of seizure rank and afterdischarge duration occurred daily with intertrial stimulation times of 30 min or less. The initial stimulations each day at these intertrial intervals showed no significant residual inhibition from the stimulations of the previous day. The longer intertrial intervals of 60 and 180 min demonstrated little inhibition of elicited seizures on day 1 for trials 2 through 4; however, after the 1st day, increased inhibition was noted for trials 2 through 4 at the 60-min intertrial interval with relatively little inhibition noted for the first trial of each day at this interval. At the longest interval tested (180 min), a significant (P <- 0.05) reduction in both the seizure rank and after discharge duration was noted with the first elicited seizure of days 3 through 5. At the 180-min interval, seizures 2 through 4 on days 3 through 5 tended to increase in length and severity rather than decrease compared with the first seizure of the day. Significant interactions occurred between the length of intertrial interval used with multiple stimulation paradigms and repeated days of testing. The short-term inhibition seen with shorter intertrial interval testing interacted in a complex and poorly understood manner with the longer term inhibition associated with daily grouped stimulations in the amygdala-kindled model of epilepsy.