Histology results showed that the stimulation electrodes were located outside the subiculum in five rats and therefore these rats were excluded from this study. For the rest of rats, the cannula was located in the CA3 area of the hippocampus and the stimulation electrode was placed in the subiculum (Fig. S2
). In total, 15 rats were included for data analysis in the stimulation (n
= 7) and sham group (n
Epileptic activities were induced after KA injection. It started with low-amplitude fast activities, increased gradually with amplitude and frequency, and finally developed into full-blown spike trains on the hippocampal channel, with or without generalization of the motor cortex channel ().
gives an overview of KA injections that the animals received on 3 days. On the first day, four rats of both groups reached SE. The number of injections did not differ in these two groups, nor did the SE percentage that day. On the second day, one rat of the HFS group did not develop convulsive seizures while two of the sham group did not display convulsive seizures. On the third day, two rats of both groups did not show generalized seizures.
Severity of seizures after each injection (max. four) over 3 days
The parameters such as number, duration, and latency of focal and generalized seizures were calculated for the three injection days (). For focal seizure number, a day effect (F(2,26) = 11.50, P < 0.01) and interaction effect between day and group (F(2,26) = 7.63, P < 0.01) were found. The number of focal seizures was 8.9 ± 1.7 in the HFS group and 25.1 ± 5.1 (mean ± SEM) in the sham group on Day 1: this difference was significant (t(13) = 2.84, P < 0.05) (). In addition, the number of focal seizures, independent of group, was less on Day 2 (t(14) = 2.90, P < 0.05) and Day 3 (t(14) = 3.23, P < 0.01) compared to Day 1.
Number, duration, and latency of focal and generalized seizures in the HFS and sham group
Represents the number of focal seizures (mean ± SEM) on 3 days in the HFS and sham groups. Note that the HFS group had less focal seizures on the first day. HFS, high frequency stimulation (300 dpi).
A logarithmic transformation was applied to the inter-seizure interval as it was not normally distributed. The inter-focal seizure interval (log) was 2.4 ± 0.1 sec in the HFS group and 2.0 ± 0.1 sec in the sham group on Day 1. Independent t-test showed that the HFS group had a longer inter-focal seizure interval (t(13) = 2.38, P < 0.05) than the sham group. Considering the low number of seizures and that a few animals were no longer responsive to KA injections on Day 2 and 3, no further tests were done.
The IS rate was calculated on 3 days for the two groups (). An overall group effect was found for the IS rate: it was lower in the HFS group (F(1,13) = 5.54, P < 0.05) than in the sham group. A day effect was also found (F(2,26) = 5.67, P < 0.01) for the IS rate. Post-hoc comparisons revealed that the IS rate on Day 1 was higher than on Day 2 (P < 0.05) and Day 3 (P < 0.05).
Figure 3 Illustrates the interictal spike (IS) rate (number/min) (mean ± SEM) over after the first seizure occurrence over 3 days. Note that the IS rate was lower in the HFS group and it also decreased over injection days. The IS rate was defined as number (more ...)
Significant day effects were also found for the latency (F(2,26) = 6.94, P < 0.01), duration of focal seizures (F(2,26) = 5.65, P < 0.01) and duration of generalized seizures (F(2,26) = 19.41, P < 0.01). Post-hoc t-test showed less duration of focal (t(14) = 2.27, P < 0.05) and generalized seizures (t(14) = 4.11, P < 0.01), and longer latency of focal seizures (t(14) = 2.95, P < 0.05) on Day 2 compared to Day 1. Similarly, the duration of focal seizures (t(14) = 2.91, P < 0.05) and generalized seizures (t(14) = 5.38, P < 0.01) were shorter, together with increased focal seizure latency (t(14) = 3.65, P < 0.01) on Day 3 compared to Day 1.