Low intensity ultrasound inhibits brain oedema formation in rats: potential action on AQP4 membrane localization

Mrigendra Bir Karmacharya, Kil Hwan Kim, See Yoon Kim, Joonho Chung, Byoung‐Hyun Min, So Ra Park, Byung Hyune Choi

Neuropathology and Applied Neurobiology 2015 · 10.1111/nan.12182

rodentex vivo tissueotherhistology molecularbehaviourother

Abstract

Aims Brain oedema is a major contributing factor to the morbidity and mortality of a variety of brain disorders. Although there has been considerable progress in our understanding of pathophysiological and molecular mechanisms associated with brain oedema so far, more effective treatment is required and is still awaited. Here we intended to study the effects of low intensity ultrasound (LIUS) on brain oedema. Methods We prepared the rat hippocampal slice in vitro and acute water intoxication in vivo models of brain oedema. We applied LIUS stimulation in these models and studied the molecular mechanisms of LIUS action on brain oedema. Results We found that LIUS stimulation markedly inhibited the oedema formation in both of these models. LIUS stimulation significantly reduced brain water content and intracranial pressure resulting in increased survival of the rats. Here, we showed that the AQP4 localization was increased in the astrocytic foot processes in the oedematous hippocampal slices, while it was significantly reduced in the LIUS-stimulated hippocampal slices. In the in vivo model too, AQP4 expression was markedly increased in the microvessels of the cerebral cortex and hippocampus after water intoxication but was reduced in the LIUS-stimulated rats. Conclusions These data show that LIUS has an inhibitory effect on cytotoxic brain oedema and suggest its therapeutic potential to treat brain oedema. We propose that LIUS reduces the AQP4 localization around the astrocytic foot processes thereby decreasing water permeability into the brain tissue.

Abstract via europepmc.

Speciesrat (Sprague-Dawley)

Subjects9 animals

Sessions per subject1

Randomisednot reported

Blindingnot reported

Sham / controlinactive transducer

Auditory controlnot reported

Readout timingoffline

Anaesthesianot reported

Readoutshistology molecular, behaviour, other — Tissue water content; intracranial pressure; neurologic deficit score; survival; AQP4 immunohistochemistry and immunoblot

Direction of effectnot assessedLIUS reduced brain water content and intracranial pressure and increased survival in the water-intoxication model, and reduced water content in OGD and glutamate slices when applied before the insult; no neural activity was measured.

Adverse eventsnot reported

Exposures

Exposure 1: Hippocampal slices, LIUS 20 min

Target: brain slice — “hippocampal slices taken in 60 mm dishes”
Device: custom-built · self-manufactured apparatus

Pulse timing
Waveform	continuous
Fundamental frequency (kHz)	1,000	✓✓✓
Pulse duration (ms)	not applicable
Pulse repetition frequency (Hz)	not applicable
Duty cycle (%)	not applicable
Sonication duration (s)	1,200	✓✓✓⚑

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	not reported
In-situ estimate	not applicable
In-situ pressure (kPa)	not applicable
In-situ Isppa (W/cm²)	not applicable
In-situ Ispta (W/cm²)	not applicable
Ispta, domain unspecified (W/cm²)	0.03, 0.05, 0.1, 0.2swept	✓✓✓

Protocol, in the paper’s words

Continuous-wave 1 MHz ultrasound at 30, 50, 100 or 200 mW/cm2 for 20 min, applied to slices in 60 mm culture dishes placed on the transducer probes, before or after (pre-US/post-US groups) oxygen-glucose deprivation or glutamate treatment.

Exposure 2: Rat craniotomy site, LIUS 10 min

Target: cerebral cortex — “craniotomy site”
Device: custom-built · self-manufactured apparatus

Pulse timing
Waveform	continuous
Fundamental frequency (kHz)	1,000	✓✓✓
Pulse duration (ms)	not applicable
Pulse repetition frequency (Hz)	not applicable
Duty cycle (%)	not applicable
Sonication duration (s)	600	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	not reported
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
Ispta, domain unspecified (W/cm²)	0.05, 0.1, 0.2swept	✓✓✓

Protocol, in the paper’s words

Continuous-wave 1 MHz ultrasound at 50, 100 or 200 mW/cm2 for 10 min applied to the craniotomy site on the ipsilateral brain 10 min after intraperitoneal water injection.

Flags from extraction

n_subjects — Only the survival cohort (WI + US, n = 9) states a number of animals exposed; total animals exposed not given; slice groups are 8-10 slices
exposures[0].unspecified_domain — Intensity (30-200 mW/cm2) is stated but not as Isppa or Ispta and no domain is given; not placed in a field, see protocol_description
exposures[1].unspecified_domain — Intensity (50-200 mW/cm2) is stated but not as Isppa or Ispta and no domain is given; not placed in a field, see protocol_description
exposures[0].timing.sonication_duration_s — 20 min converted to 1200 s; 10 min to 600 s for the in vivo exposure
conditions — Brain oedema is not in the condition vocabulary; recorded as other
anaesthesia — Rats were anaesthetised for surgery and ICP recording; anaesthesia during sonication not stated