Persistence of Acquired Epileptogenesis in Amygdaloid-Kindled Rats: Relationship between the Initial Kindling Stages and Seizure Development in Rekindling

In order to gain insight into mechanisms underlying the persistence of the partial kindling effect, we suspended amygdaloid kindling at different seizure stages in rats, and investigated the effects on subsequent rekindling after a rest period of 2 months. Ten-week-old rats, implanted with bipolar electrodes, were separated by various initial kindling stages into 5 groups of rats, partially kindled to stages 1 (n = 7) and 2 (n = 10), fully kindled to stages 4 (n = 11) and 5 (n = 11), and control rats (n = 12) which were implanted but not stimulated initially. The number of stimulations required to elicit the first stage 5 seizure during rekindling was significantly lower in the fully kindled groups (P < 0.01 in the stage 4 group and P < 0.001 in the stage 5 group) than the control group. The cumulative afterdischarge duration during rekindling was significantly shorter in the fully kindled groups (P < 0.01 in both groups) than the control group. The latency of the first stage 5 seizure during rekindling was significantly shorter in the partially and fully kindled groups than the control group. These results suggest that epileptogenesis acquired at the partially kindled stage is different than that acquired at the fully kindled stage. However, the effects of the initial kindling on the latency to produce the stage 5 seizure during rekindling persisted both in the partially and fully kindled rats.