Pulsed Focused Ultrasound Reduces Hippocampal Volume Loss and Improves Behavioral Performance in the Kainic Acid Rat Model of Epilepsy.

Focused ultrasound (FUS) has the potential to modulate regional brain excitability and possibly aid seizure control; however, effects on behavior of FUS used as a seizure therapy are unknown. This study explores behavioral effects and hippocampal restoration induced by pulsed FUS in a kainic acid (KA) animal model of temporal lobe epilepsy. Twenty-nine male Sprague-Dawley rats were observed for 20 weeks with anatomical magnetic resonance imaging (MRI) and behavioral performance evaluations, comprising measures of anxiety, limb usage, sociability, and memory. FUS targeted to the right hippocampus was given 9 and 14 weeks after KA was delivered to the right amygdala. Ultrasound pulsations were delivered with the acoustic settings of 0.25 of mechanical index, 0.5 W/cm<sup>2</sup> of intensity spatial peak temporal average (I<sub>SPTA</sub>), 100 Hz of pulse repetition frequency, and 30% of duty cycle, during three consecutive pulse trains of 10 min separated by 5-min rests. Controls included normal animals with sham injections and KA-exposed animals without FUS exposure. Longitudinal MRI observations showed that FUS substantially protected hippocampal and striatal structures from KA-induced atrophy. KA alone increased anxiety, impaired contralateral limb usage, and reduced sociability and learning. Two courses of FUS sonications partially ameliorated these impairments by enhancing exploring and learning, balancing limb usage, and increasing social interaction. The histology results indicated that two sonications enhanced neuroprotection effect and decreased the inflammation markers induced by KA. This study supports existence of both neuroprotective and beneficial behavioral effects from low-intensity pulsed ultrasound in the KA animal model of epilepsy.

Introduction

Purpose Transcranial ultrasound stimulation

Study Objective To evaluate whether low-intensity pulsed focused ultrasound provides neuroprotective and behavioral benefits in a kainic acid–induced rat model of temporal lobe epilepsy.

Animal model / Human subject Rat (Sprague–Dawley), age not specified (weight 290–330 g), male

Disease model temporal lobe epilepsy (kainic acid-induced)

MRI or image guidance method Atlas overlay (brain atlas) with transducer positioning to aim at the right hippocampus — no MRI-, image-, or stereotactic-guided targeting reported.

Targeted brain region(s) Hippocampus

Target coordinates AP: -2.3 mm, ML: +4.5 mm, DV: -8.2 mm (from bregma)

Cargo name and characteristics Kainic acid (small-molecule excitotoxin): 750 ng injected into the right amygdala via glass capillary (20 ng/s flow); used to induce excitotoxic hippocampal damage and model temporal lobe epilepsy (causes status epilepticus and chronic seizures).

Route of administration Intra‑amygdala (stereotaxic intracerebral) injection via glass capillary tubing

Outcomes and Safety

Summary of Outcomes Two courses (5 weeks apart) of low‑intensity pulsed FUS (MI 0.25; ISPTA 0.5 W/cm2; PRF 100 Hz; 30% duty cycle; three sequential 10‑min pulse trains separated by 5‑min rests) partially protected against KA‑induced hippocampal and striatal atrophy and reduced microglial (IBA‑1) inflammation, and produced behavioral improvements including reduced anxiety (increased open‑field center exploration), increased sociability, improved contralateral limb usage symmetry, and partial restoration of learning/memory; two treatments were more effective than one.

Duration of biological effect more than 2 months

Safety-related matter The authors report no gliosis or chronic inflammatory effects at the sonicated site and state that I_SPTA 0.5 W/cm^2 FUS did not injure brain tissue with these parameters; however, they caution that higher exposure levels can cause tissue injury, off-target effects cannot be fully ruled out, and parameter adjustments would be needed for translation to humans.

Brain Region

Ultrasound Parameters

Ultrasound instrument Focused ultrasound transducer (Sonic Concept, U.S.; fundamental frequency 0.5 MHz; radius of curvature 64.3 mm). -6 dB pressure field diameter 4 mm, axial length 23 mm.

FUS Frequency 0.5 MHz (carrier); 100 Hz pulse repetition frequency (PRF)

FUS Intensity 0.5 W/cm^2 (I_SPTA); 1.67 W/cm^2 (I_SPPA); 0 W/cm^2 (sham)

FUS Pressure 0.177 MPa

FUS Mode pulsed

Pulse duration 3 ms

Duration of a single FUS session 40 minutes

Focal Characteristics Focal depth: 23 mm; Focal length: 64.3 mm; Aperture size: None

Treatment frequency multiple sessions

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