Focused ultrasound suppresses pentylenetetrazol-induced epileptiform activity in rats and alters connectivity measured by functional MRI.

Focused ultrasound (FUS) has emerged as a promising neuromodulation technique for reducing regional brain excitability, offering a potential therapeutic approach for drug-resistant epilepsy (DRE). However, its underlying mechanisms remain unclear, particularly regarding functional connectivity alterations in seizure-related brain networks. This study investigates the relationship between FUS-induced seizure suppression and brain functional connectivity using EEG and resting-state fMRI (rs-fMRI). Using a pentylenetetrazol (PTZ)-induced epilepsy rat model (n = 28), we applied burst-mode FUS with 0.25 MI, I<sub>SPTA</sub> = 0.3 W/cm<sup>2</sup> with low (30s-on-90s-off)/high (90s-on-30s-off) doses with 10-minute sonication durations to the anterior nucleus of the thalamus (ANT), resulting in approximately 36% reduction in hippocampal spike activity. Rs-fMRI analysis (36 × 36 connectivity matrix) revealed that the PTZ-induced seizure reduction strongly correlates with significant whole-brain connectivity changes, including a 45.1% decrease in connectivity between the anterior thalamic and hippocampal networks. Histological analysis confirmed that FUS preferentially modulates key brain regions involved in epileptic circuits, particularly the thalamus and hippocampus. These findings provide compelling evidence that FUS selectively alters seizure-related functional networks, highlighting its potential as a noninvasive therapeutic approach for epilepsy.

Introduction

Purpose Transcranial ultrasound stimulation

Study Objective To determine whether focused ultrasound targeting the anterior nucleus of the thalamus reduces seizures and alters seizure-related functional brain connectivity, assessed by EEG and resting-state fMRI, in a PTZ-induced rat epilepsy model.

Animal model / Human subject Rattus norvegicus (Sprague-Dawley), age not specified (weight 290–340 g), male

Disease model Epilepsy (PTZ-induced)

MRI or image guidance method MRI-guided

Targeted brain region(s) Thalamus

Target coordinates FUS (ANT): AP -2.5 mm, ML 0 mm, DV 6.0 mm; Electrode (hippocampal CA1): AP -9.0 mm, ML 4.5 mm, DV 9.0 mm

Outcomes and Safety

Summary of Outcomes Focused ultrasound (FUS) targeting the anterior nucleus of the thalamus suppressed PTZ‑induced epileptiform activity (~29–42% spike reduction, ~36% hippocampal spike reduction) and normalized functional connectivity, most prominently reducing thalamus–hippocampus connectivity (~45% decrease) with reduced c‑Fos in thalamus and hippocampus and no histological damage. Both burst‑mode paradigms were effective: 0.25 MI, I_SPTA = 0.3 W/cm^2, 30% duty cycle, 10‑minute sonication to ANT using either 30 s ISI (high‑dose) or 90 s ISI (low‑dose).

Duration of biological effect 10-20 min

Safety-related matter Histological analysis showed no tissue damage detectable, immune cell infiltration, or microglial activation following FUS treatment

Brain Region

Ultrasound Parameters

Ultrasound instrument Custom focused ultrasound transducer (1 MHz, radius of curvature = 16 mm); -6 dB pressure-field diameter = 1.5 mm, axial length = 4 mm. Function generator: AFG-3022 (GW Instek, Taiwan); RF power amplifier: 210L (E&I, USA); Needle hydrophone: HNA-0400 (ONDA Corp., Sunnyvale, CA, USA).

FUS Frequency 1 MHz

FUS Intensity 0.3 W/cm2

FUS Mode pulsed

Duration of a single FUS session 10 minutes (600 s)

Focal Characteristics Focal depth: 4 mm; Focal length: 16 mm; Aperture size: None

Treatment frequency Single session

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