Authors :
Presenting Author: Hyang Woon Lee, MD, PhD – Ewha Womans University School of Medicine
YuJaung Kim, PhD – Ewha Womans University School of Medicine
Yun Seo Choi, PhD – Ewha Womans University School of Medicine
Sol Ah Kim, MS – Ewha Womans University School of Medicine
Seoyun Chang, MS – Sungkyunkwan University
Jinhyoung Park, PhD – Sungkyunkwan University
Rationale:
Focused ultrasound (FUS) has emerged as a promising, non-invasive tool for precisely modulating specific brain regions, offering potential therapeutic approaches for neurological disorders like epilepsy. In this study, we investigated the application of FUS for modulating the hippocampal network, aiming to suppress epileptic discharges in an optogenetic rat model of temporal lobe epilepsy (TLE).
Methods:
A well-established TLE rat model was employed, induced by intrahippocampal microinjection of kainic acid mimicking human TLE. To induce epileptic discharges, CAMKII-positive excitatory neurons were targeted for ChR2 expression in the hippocampus. AAV5-CaMKIIa-hChR2-EYFP was injected into the right hippocampus (ML: +3.2 mm, AP: -4.56 mm, DV: -3.8 mm from bregma). After a 6-week period, ptical fiber and local field potential (LFP) microelectrodes were implanted. Epileptic discharges were induced using 473 nm blue-light stimulation with a train of 200 pulses with a frequency of 40 Hz for 5s duration, starting at 80 mW/mm2 intensity. FUS was applied using two different sonication protocols (5 and 10 seconds) with 5000 cycles, 1 MHz center frequency, 100 Hz pulse repetition frequency, 50% duty cycle, and 0.4 MPa pressure. To evaluate the effects of FUS on seizure suppression, three interventions were employed randomly: 1) optogenetic stimulation alone, 2) optogenetic stimulation combined with 5-sec FUS, and 3) optogenetic stimulation combined with 10-sec FUS. The number of spikes was measured during induced seizures to compare the effects of seizure suppression.Results:
Optogenetic stimulation successfully induced seizure-like events (SLEs) by activating CaMKII-positive neurons in the hippocampus, with SLE durations ranging from 2 to 73 seconds. In the condition when optogenetic stimulation alone was applied, the number of spikes did not decrease, indicating sustained epileptiform activity throughout the induced epileptic discharge. When FUS was applied in combination with optogenetic stimulation, the SLE duration and spike frequency were significantly reduced, indicating that it effectively suppressed epileptic discharges.
Conclusions:
This study demonstrates that the combination of FUS with optogenetic stimulation effectively modulates epileptic activity in TLE rat model. The ability to reliably induce and subsequently suppress epileptic discharges by targeting CaMKII-positive excitatory neurons in the hippocampus, suggests that optogenetics and FUS can serve as valuable tools for elucidating the neural mechanisms of epileptogenesis and developing potential therapeutic strategies. The non-invasive nature of FUS, combined with the precise neuromodulation technique for suppressing epileptic discharges without damaging brain tissue. Future research will focus on further optimizing FUS parameters and investigating the long-term effects on seizure suppression.
Funding:
Basic Science Research (RS-2023-00265524) and BK21 Plus Programs by NRF, the Korea Health Technology R&D Project through the KHIDI (HI23C1532), IITP grant (No. RS-2022-00155966) by the MSIT and AI Convergence Innovation Human Resources Development of Ewha Womans Univ.