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

Po-Chun Chu, Hsiang-Yu Yu, Cheng-Chia Lee, Robert Fisher, Hao-Li Liu

Neurotherapeutics 2022, 19, 1368-1380 · 10.1007/s13311-022-01250-7

rodentepilepsyeeg meghistology molecular

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 cm 2 , 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/cm 2 , 30% duty cycle for 10-min sonications (group effect, F (4, 15) = 6.321, p SPTA 0.5 W/cm 2 , 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.

Abstract via europepmc.

Speciesrat (Sprague-Dawley)

Subjects25 animals

Sessions per subject1

Randomisednot reported

Blindingsingle

Sham / controlinactive transducer

Auditory controlnot reported

Readout timingboth

Anaesthesiaanaesthetised

Readoutseeg meg, histology molecular — EEG epileptiform spike/burst counts and durations; electrographic seizure frequency; histology (H&E, GFAP immunohistochemistry); hippocampal volume

Direction of effectinhibitoryFUS reduced EEG epileptiform spike counts, burst counts, burst durations, and electrographic seizure frequency relative to KA-only controls, with higher-intensity regimens producing greater and more prolonged suppression at the cost of tissue inflammation/gliosis.

Adverse eventsobservedIn group 3 (0.75 MI, 2.8 W/cm2), animals showed various degrees of inflammatory cell infiltration and one showed tissue necrosis in FUS-treated hippocampus/thalamus, comparable to KA-only animals. In group 6 (0.25 MI, 0.5 W/cm2), FUS treatments significantly normalized inflammatory-like gliosis and produced neither gliosis nor necrosis in normal (non-KA) animals exposed to the same parameters (n=2).

Exposures

Exposure 1: Pulsed FUS to right hippocampus (4 parameter regimens: groups 3-6)

Target: hippocampus — “right hippocampus (CA1, CA2, CA3)”
Device: Sonic Concepts · SonicConcept ✓

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	500	✓✓✓
Pulse duration (ms)	not reported	⚑
Pulse repetition frequency (Hz)	not reported	⚑
Duty cycle (%)	30, 5, 1, 30swept	✓✓✓
Sonication duration (s)	600, 300, 300, 600swept	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	2.8, 0.5, 0.1, 0.5swept	✓✓✓⚑
In-situ estimate	not reported
In-situ pressure (kPa)	not reported
In-situ Isppa (W/cm²)	not reported
In-situ Ispta (W/cm²)	not reported

Protocol, in the paper’s words

FUS exposure level was set at 0.75 MI in groups 3, 4, and 5 and 0.25 MI in group 6. The exposure duration was either three consecutive 5-min (groups 4 and 5) or 10-min (groups 3 and 6) 'on' periods, with a 5-min 'off' period between each 'on' period, delivered in a single session at week 7. Groups (duty cycle, ISPTA, duration): group 3 = 30%, 2.8 W/cm2, 10 min*3; group 4 = 5%, 0.5 W/cm2, 5 min*3; group 5 = 1%, 0.1 W/cm2, 5 min*3; group 6 = 30%, 0.5 W/cm2, 10 min*3.

Flags from extraction

n_subjects — Abstract states 'Forty-four male Sprague-Dawley rats' while Methods states 'Forty-three male Sprague-Dawley rats'; n_subjects (25) is the number of KA-injected rats treated with FUS per Methods and Table 1 (9+5+6+5). An additional 4 non-KA rats were exposed to FUS only for histology/safety testing and are not included in this count.
exposures[0].timing.pulse_duration_ms — Paper reports duty cycle, mechanical index, and on/off period durations for each group but does not state pulse duration or PRF numerically anywhere in the text.
exposures[0].timing.pulse_repetition_frequency_hz — Not stated numerically; only duty cycle and 'on'/'off' period durations are given.
exposures[0].free_field.ispta_w_cm2 — List order corresponds to groups 3, 4, 5, 6 as given in Table 1 (2.8, 0.5, 0.1, 0.5 W/cm2 respectively), matched to duty_cycle_pct and sonication_duration_s lists in the same order.