Pulsed-Focused Ultrasound Provides Long-Term Suppression of Epileptiform Bursts in the Kainic Acid-Induced Epilepsy Rat Model

Abstract

Focused ultrasound (FUS) has potential utility for modulating regional brain excitability and possibly aiding seizure control; however, the duration of any beneficial effect is unknown. This study explores the efficacy and time course of a short series of pulsed FUS in suppressing EEG epileptiform spikes/bursts in a kainic acid (KA) animal model of temporal lobe epilepsy. Forty-four male Sprague-Dawley rats were recorded for 14 weeks with EEG while software calculated EEG numbers of epileptiform spikes and bursts (≥ 3 spikes/s). Four regimens of FUS given in a single session at week 7 were evaluated, with mechanical index (MI) ranging from 0.25 to 0.75, intensity spatial peak temporal average (I_SPTA) from 0.1 to 2.8 W per cm², duty cycle from 1 to 30%, and three consecutive pulse trains for 5 or 10 min each. Controls included sham injections in four and KA without FUS in eleven animals. Histological analysis investigated tissue effects. All animals receiving KA evidenced EEG spikes, averaging 10,378 ± 1651 spikes per 8 h and 1255 ± 199 bursts per 8 h by weeks 6-7. The KA-only group showed a 30% of increase in spikes and bursts by week 14. Compared to the KA-only group, spike counts were reduced by about 25%, burst counts by about 33%, and burst durations by about 50% with FUS. Behavioral seizures were not analyzed, but electrographic seizures longer than 10 s declined up to 70% after some FUS regimens. Repeated-measure ANOVA showed a significant effect of higher intensity and longer sonication duration FUS treatment using 0.75-MI, I_SPTA 2.8 W/cm², 30% duty cycle for 10-min sonications (group effect, F (4, 15) = 6.321, p < 0.01; interaction effect, F (44, 165) = 1.726, p < 0.01), with the hippocampal protective effect lasting to week 14, accompanied by decreased inflammation and gliosis effect. In contrast, spike and burst suppression were achieved using an FUS regimen with 0.25-MI I_SPTA 0.5 W/cm², 30% duty cycle for 10-min sonications. This regimen reduced inflammation and gliosis at weeks 8-14 and protected hippocampal tissue. This study demonstrates that low-intensity pulsed ultrasound can modulate epileptiform activity for up to 7 weeks and, if replicated in the clinical setting, might be a practical treatment for epilepsy.

Keywords: Focused ultrasound; Kainic acid model; Neuromodulation; Temporal lobe epilepsy.

Fig. 1

Atlas showing the KA injection site (amygdala, marked as BLA [28]), electrode position, and appearance of model

Fig. 2

Conceptual schematic of the sonication setup and topographical sonication depth, which targeted at hippocampus area (marked as CA1, CA2, and CA3 in the atlas [28])

Fig. 3

A Time course of experiment protocol. B Photos of EEG recording and EEG example. C Conceptual schematic of the sonication on groups 3, 4, 5, and 6

Fig. 4

Typical example of EEG signal of non-KA model, KA model, and post-FUS KA model. Example showing examples of spikes, burst count, and burst duration

Fig. 5

Comparison of the EEG signals for various groups (observation period: week 2–14, within 8 h per week). A Spike number. B Burst number. C Burst duration. FUS sonications were delivered at the end of week 7 (marked as blue dashed line). ^# denotes significant difference between the non-KA group and KA only group, p < 0.05; ^##p < 0.01; ^###p < 0.001. *denotes significant difference between KA + FUS group and KA only group, p < 0.05; **p < 0.01; ***p < 0.001

Fig. 6

Comparison of the averaged EEG signals in various groups (observation period: week 6–14, within 8 h per 2 weeks). A Spike number. B Burst number. C Burst duration. FUS sonications were delivered at the end of week 7 (marked as blue dashed line). * denotes significant difference between groups, p < 0.05; **p < 0.01; ***p < 0.001

Fig. 7

Comparison of the HE and GFAP staining among the testing group including groups 1, 2, 3, and 6

Fig. 8

Comparison of the hippocampus volume and GFAP positive signal among the testing group, including groups 1, 2, 3, and 6. A GFAP-positive signal change, with the contralateral hippocampus as the basis. B hippocampal volume change, with the contralateral hippocampus as the basis. * denotes a significant difference between groups, p < 0.05; **p < 0.01; ***p < 0.001